Unit 01-08 - 3rd Ed. RDS (IADC-PETEX) - Diesel Engines and Electric Power PDF
Unit 01-08 - 3rd Ed. RDS (IADC-PETEX) - Diesel Engines and Electric Power PDF
Unit 01-08 - 3rd Ed. RDS (IADC-PETEX) - Diesel Engines and Electric Power PDF
UNIT I • LESSON 8
by Ron Baker
Published by
FE lEX PETROLEUM EXTENSION SERVICE
The University of Texas at Austin
Continuing Education
Austin, Texas
in cooperation with
INTERNATIONAL ASSOCIATION
OF DRILLING CONTRACTORS
• Houston, Texas
1998
Library of Congress Cataloging-in-Publication Data
power.
DIESEL E~GI0JES
Introduction I
Power'rranmission I
Electric Transmission 3
Diesel Engines 5
Engine Fuels 6
Spark Ignition 7
Natural Aspiration 9
Forced-Air Induction 10
10 Summarize I I
Intake Stroke 14
Compression Stroke 14
Power Stroke 14
Exhaust Stroke 14
Lugging Power 17
Combustion Cup 19
Fuel Injector 19
To Summarize 20
Two-Stroke Power 21
To Summarize 14
III
Diesel Fuel 25
Fuel Quality 26
Volatility 26
Viscosity 27
Sulfur Content 27
Flash Point 28
Pour Point 28
Acid Corrosiveness 28
To Summarize 31
Fuel Pump 33
Excess Fuel 33
Transfer Pumps 42
Pump Sizing 42
Pump Location 42
Fuel Lines 42
Starting an Engine 44
Air Knocking 45
Removing Air 45
To Summarize 45
Fuel-Injection Systems 47
Fuel-Injection Rate 48
Fuel Atomization 48
Multipump Injectors 49
IV
Distributor Injection 61
Common-Rail Injection 64
To Summarize 66
Governors 67
Centrifugal Force 68
lYres of Governor 69
Variations in Speed 74
To Summarize 78
Lubrication Systems 81
Oil Pumps 82
Relief Valves 82
Strainers 83
Filters 83
Oil Coolers 86
Crankshaft Lubrication 89
Piston Lubrication 89
Camshaft Lubrication 89
Explosion Covers 93
Oil Quality 93
Detergent Oils 95
Oil Contamination 95
Oil Testing 95
To Sununarize 96
Cooling Systems 97
Coolant 97
Radiators 98
Fins 98
Engine Fans 98
Heat Exchangers 99
v
CoohIlt j.\o\\ 100
Fans 102
Fins J04
.\irFlow 105
Dirt J06
()xygen 106
To Summarize 112
Air Cleaners 1 T4
Turbochargers 122
Aftercoolers 124
To Summarize T2 5
Purposes 127
Mufflers 130
To Summarize 132
VI
Electric Starters 134
Direct Current Versus Alternating Current J 35
Starter System Parts 135
How Electric Starters \,york J 36
Generators and Cutouts [37
Batteries 138
Air-Motor Starters 139
Air Requirements 140
Cleaning an Air Starter 140
Hydraulic Starters 140
Gasoline Engine Starters 141
Compressed-Air Starting 142
To Summarize 144
Instruments 145
Pyrometers 145
Estimating Engine Load 145
Cylinder Temperatures. 146
Dividing Loads Equally 146
Oil-Pressure Gauges 146
Low Oil Pressure 146
High Oil Pressure 147
Oil-Temperature Gauges 148
Lower-than-Normal Oil Temperature 148
Higher-than-Nonnal Oil Temperature 148
Coolant-Temperature Gauges 148
Inlet Versus Outlet Temperature 149
Air Manifold-Pressure Gauge 149
Dirty Air Filters 149
Tachometers 149
To Summarize 150
VII
Engine Wann-Up 160
To Summarize 164
Reports 165
To Summarize 168
Introduction 169
DC Generators 172
AC Generators 175
To Summarize 176
Exciters 178
Maintenance 185
Malfunctions 193
To Summarize 195
Glossary 197
VIII
Frontispiece: Diesel engines and electric generators power an offshore
ng. XIV
Figures
1. Large internal combustion engines power drilling rigs.
2. Prime movers and the compound in a mechanical drive 2
7. Supercharger (blower) 10
12. Cam 23
14. Fuel system showing vented fuel tank, strainer, filter, pump, and
injectors 34
IS· Tank-typefuelfilters 37
to each cylinder 50
IX
33. Rack and pinion controls fuel metering. 67
34. Centrifugal force moves a steel bolt on a string away from center
of spin. 68
70
44. Lube oil system of a diesel engine showing oil cooler bypass
x
64· Approximate sizt's for diesel engine exhaust piping 129
unit 135
engines 136
Table
XI
XII
Foreword
Ron Baker
XIII
Acknowledgments
xv
Units of Measurement
XVI
English-Units-to-SI-Units Conversion Factors
r-r-'he main purpose ofa rotary rig is to drilJ, or make, a hole. To Engine Power and
.1 make hole, the rig must have asource ofpower. \\!hat is more, Transmission
the rig must be able to transmit this power to equipment that needs
it. For example, the mud pumps need power to move driJIing fluid.
The drawworks also needs power to do its work.
Usually, large internal combustion engines power the rig (fig. I).
A mixture of fuel and air bums inside the engine to make it run. If
the engine is running correctly, the fuel-air mixture burns at a
controlled rate. Keep:in mind that an engine must get oxygen from
the atmosphere before the fuel can burn.
I
DIESEL ENGINES
Power Transmission A rig owner does not install an engine on each piece of equipment
that needs power. It is more practical to set up two, three, or more
powerful engines at a single place on the site. Special equipment
attached to the engines then transmits power to the equipment that
needs it. Offshore, for example, the rig builder may put three or
four mgines in an engine room that is some distance from the
drav,rworks and the mud pumps. On land rigs, the rig-up crew often
placl:s the engines next to the rig floor, or crew members may place
them inside a special house or shed that is several yards (metres)
from the equipment needing the power.
Mechanical Transmission Some rigs use machinery (gears, sprockets, and chains) to transmit
and the Compound engine power. If machinery transmits power, the rig has amechani
cal transmission. In a mechanical transmission, the rig builders
mow1t couplings on each engine. These couplings connect the
engines to the machinery that transmits the engine power.
Crew members call the heavy-duty sprockets and chains that
make up this machinery the compound. The rig-up crew connects
the compound to the engine couplings and to the equipment
Figure 2. Prime movers needing power, such as the drawworks and the mud pumps. The
and the compound in a compound can then transfer engine power to the equipment (fig. 2).
mechanical drive
TO THE DRAWWORKS
2
INTRODUcnON
~\;lany rigs do not use a compound to transmit engine power. Instead, Electric Transmission
they use electricity. On electric rigs, a large electric generator is
attached to each engine. The engines run the generators (fig. 3). The
generators, in turn, make electricity, which they send through heavy
duty wires (cables) and special controls to powerful electric motors
(fig. 4)' These electric motors power the equipment. Usually, the rig
owner places the motors on or next to the equipment being powered.
3
DIESEL ENGINES
Engines Versus An engine and amotor are similar devices: both provide powerto drive
Motors the equipment. They are so similar that many people call an engine a
motor. Strictly speaking, however, an engine and a motor are differ
ent. An engine changes thermal energy into power to produce force
and motion. A motor, on the other hand, creates power without
having to change or transform its energy source. Energy is neither
created nor destroyed, although its form may be changed.
On rigs, for example, the engines change the heat energy from
burning fuel into mechanical energy. The mechanical energy runs
generators to make electrical energy. Using this electrical energy, the
motors then power equipment; however, the motors run on electricity
and therefore do not convert it to another form of energy.
4
Diesel Engines
T
T
T
E ngines take in air and fuel. They bum this air and fuel mixture
to create energy to do work.
Engines bum fuel and air to move pistons up and down in
How Engines
Operate
cylinders (fig. 5)' Intake valves or intake ports let air into each
cylinder, where it mixes with the fuel. A spark or some ot.her heat
source ignites the mixture of air and fuel. As the fuel-air mixture
bums, it expands to move the pistons. Burned gases leave· the
cylinders through exhaust valves.
INTAKE
VALVE
EXHAUST
VALVE
CYLINDER
FILLED WITH
FUEL AND AIR
PISTON
5
DIESEL ENGINES
Engine Fuels
Manufacturers make a variety of internal combustion engines that
burn different kinds offuel. Most automobile engines, for example,
run on gasoline; however, rig engines run on natural gas, liquefied
petroleum gas (LPG) such as butane and propane, or diesel fuel.
Most rig engines operate on diesel fuel. Rig owners use natural gas
or LPG engines only if the fuels are near the rig site, for example,
if the rig is drilling near a natural gas processing plant. The choice
of diesel power for rigs is based on the factors listed below.
I. Because of the special way it uses fuel, a diesel engine
produces more twisting force (torque) than a gas or an LPG
engine of the same size. More torque means more drilling
power.
2. Diesel fuel is more portable than natural gas. Rig owners
cannot easily transport natural gas or store it in tanks. To
have enough to run the engines, they would have to com
press the gas to a very high degree, which would require
expensive high-pressure tarlks.
3. Even though LPG is more easily transported than natural
gas, it changes readily to avapor, and this vapor is very flam
mable. Because diesel fuel does not vaporize as readily as
LPG, it is safer to transport, handle, and store than is LPG.
6
DIESEL ENGINES
Natural gas, LPG, and diesel engines differ in two main ways Gas or LPG Engines
1. they use different fuels, and
and Diesel Engines
2. they use different methods to ignite the fuels.
Natural gas and LPG engines use spark plugs. Aspark plug creates Spark Ignition
a high-voltage electric spark that fires, or ignites, the fuel-air
mixture inside the engine's cylinders. Gas and LPG engines are
therefore spark ignition (SI) engines.
Some diesel engines have glow plugs. Although these may look
like spark plugs, glow plugs only help start a diesel engine in cold
weather by preheating the combustion chamber. They do not
ignite the fuel-air mixture after the engine starts. In the text that
follows, you will see how diesels ignite fuel without spark plugs.
Combustion is the controlled burning of fuel and air. Natural gas Fuel-to-Air Ratio in Spark
and LPG (51) engines draw fuel and air into the cylinders, where Ignition (51) Engines
combustion occurs. To run well, SI engines need the right propor
tion, or ratio, of fuel to air. While a mixture of too much fuel with
too little air may not burn, mixing too little fuel with too much air
may also fail to produce combustion.
Gas and LPG engines run best on a mixture of about 15 parts
air to I part fuel. This 15 -to- I ratio holds true no matter how little
or how much the engine throttle is opened. So when the driller
opens the throttle to increase the engine's speed, more fuel goes
into the cylinders. At the same time, more air also goes in to keep
the mixture at about 15 to one.
Conversely, when the driller decreases the engine's speed, less
fuel and less air go into the cylinders. Designers of gas and LPG
engines build them so that the fuel-to-air ratio stays at about 15 to
I regardless of speed.
As mentioned before, spark plugs do not ignite the fuel-air mixture Compression Ignition (0)
in a diesel engine; very hot air ignites the fuel. Anytime you Engines
compress air, its temperature increases. Compress it enough, and
the temperature becomes hot enough to ignite fuel.
Engine pistons compress the air inside the cylinders. In a
diesel, they compress the air so much that the fuel-air mixture
ignites. Diesel engines are therefore compression ignition (CI)
engines. Adiesel's piston compresses the air until the temperature
reaches about 1,000° Fahrenheit (F) or about 540° Celsius (C). A
fuel injector then sprays diesel fuel into the cylinder, where it
ignites.
7
DIESEL ENGINES
Fuel-to-Air Ratio in Think about a spark-ignition engine for a moment. Suppose the
Compression Ignition driller needs to speed the engine up.1'o do so, the driller moves the
(C1) Engines engine's throttle to increase the amount of fuel going into the
cylinders. At the same time, the engine also takes in more air.
Remember that the fuel-to-air ratio has to be about 15 to I in an
S1 engine, regardless of its speed.
Now consider a diesel engine, Diesels (C1 engines) work differ
ently from S1 engines. C1 engines draw in a constant amount of air,
regardless of their speed. When the driller moves the throttle to
increase the fuel to the cylinders, the engine does not take in any more
air. Since the air in the cylinder is so hot, diesel fuel and air ignite no
matter how much fuel the injector puts in. The fuel-to-air ratio is not
as critical in a C1 engine, as long as enough oxygen exists to suppon
combustion.
Strokes and Cycles T ~o types of diesel engines are four-strokes-per-cycle and two
strokes-per-cycle. A cycle is a series ofevents that happen when an
engine runs. A stroke is the piston's upward-or-downward move
ment in the engine's cylinders. Strokes-per-cycle is the number of
strokes a piston makes to complete one operating cycle.
T wo-strokes-per-cycle means that the piston goes down one
stroke and up one stroke to complete one operating cycle. Four
strokes-per-cycle means that the piston goes down one stroke, up
asecond stroke, down again for athird stroke, and then up again for
a fourth stroke to complete one operating cycle.
A piston makes one stroke downward when it goes from its
highest point in the cylinder to its lowest point. It makes one stroke
upward when it goes from its lowest point in the cylinder to its
highest point (fig. 6). The highest point is top dead center, orTDC.
The lowest point is bottom dead center, or BDC.
Most people use ashorter expression for two-strokes-per-cycle
and four-strokes-per-cycle. Some shorten the terms to two-cycle
and four-cycle, while otl1ers use the expressions two-stroke and
four-stroke. The latter expressions will be used in this manual.
8
DIESEL ENGINES
Manufacturers get air into a diesel engine's cylinders in one of two Forced-Air
ways- Induction and
I. they naturally aspirate it; or
Natural Aspiration
2. they force air into it.
9
DIESEL ENGINES
Forced-Air Induction Some engines use special devices to compress and force atmo
spheric air into the cylinder. These devices can be superchargers
(also called blowers) or turbochargers. The engine's crankshaft
drives a supercharger (blower) which supplies high-pressure air to
the engine (fig. 7)' Inside the blower are blades or impellers, which
act something like fan blades. The engine turns these impeJJers.
HOUSING
Figure 7. Supercharger
(bl(flJ)er)
10
DIESEL ENGINES
Forcing air into an engine makes it more powerful. Since the Forced-Air Induction and
supercharger or turbocharger compresses the air within it, that air Power
is denser (wei ghs more) than atmospheric air. Forced-air induction
thus packs more air into the cylinder. With more air, the fuel can
burn more completely, which results in more power. Typically, a
supercharged or turbocharged diesel engine is about one-third
more powerful than a naturally aspirated engine of the same size.
Manufacturers can supercharge or turbocharge both two
stroke and four-stroke diesel engines. Only four-stroke diesel
engines, however, can be naturally aspirated. You will learn why
two-stroke diesels must be supercharged or turbocharged in the
section on two-stroke diesel engines. (Note that both two-stroke
and four-stroke gasoline engines can be supercharged, turbo
charged, or naturally aspirated.)
To summarize-
II
DIESEL ENGINES
nngille fuels
• ,\lost rig engines run un diesel fuel, although a few may nm
on natural gas or LPG.
• Diesel engines are compression ignition (el) engines.
• Gas and LPG engines are spark ignition (SI) engines.
St7'okes and cycle.1
• Diesel engines are either four-stroke-per-cycle or two
stroke-per-cycle engines.
• Two strokes per cycle means that the piston goes down one
stroke and up one stroke to complete a firing cycle.
• Four strokes per cycle means that the piston goes down one
stroke, up asecond stroke, down again for a third stroke, and
up again for the fourth stroke.
Forced-air induction and natural aspiration
• Nahlral aspiration means the engine draws in air from the
atmosphere without any mechanical (or other) assistance.
• Forced-air induction means that a machine (a supercharger
or a turbocharger) supplies air to the engine at a pressure
higher than that of the atmosphere.
• Supercharged and wrbocharged engines are more powerful
than naturally aspirated engines ofthe same size because the
compressing atmospheric air packs more oxygen into the
cylinder. With more oxygen, the fuel can burn more com
pletely, which results in more power.
12
DIESEL ENGINES
Figure 8 shows the four strokes of the firing cycle of a naturally Four-Stroke Diesel
aspirated, four-stroke diesel engine. ;\ote the piston, the cylinder, Engines
the intake valve, and the exhaust valve.
a. INTAKE b. COMPRESSION
c. POWER d. EXHAUST
13
DIESEL ENGINES
Intake Stroke On the intake stroke of the cycle, the piston moves down. This
downward movement creates a vacuum in the cylinder. Atmospheric
pressure isnow higher than the pressure in the cylinder, causing air to
enter through the open intake valve and fill the vacuum.
Compression Stroke On the compTessionstroke, the intake valve closes. The piston moves up
and compresses the air. Compression raises the air's temperature to
about J ,ooo°F (S4ooq, the temperature at which diesel fuel ignites.
Power Stroke On the power stroke, a diesel fuel injector sprays fuel into the
cylinder. Ignited by the heat of compression, the burning fuel
generates gases that expand to force the piston down. This power
rotates the engine's crankshaft and flywheel.
Exhaust Stroke On the exhaust stroke, the exhaust valve opens, and the rising piston
pushes out the used gases.
The Four-Stroke Cycle In a four-stroke engine, four strokes make up a firing cycle
• 1st stroke, down-air intake;
• 2nd stroke, up-compression;
• 3rd stroke, down-power; and
• 4th stroke, up-exhaust.
Four-Stroke Engines and In a four-stroke engine, the piston makes one stroke each for
Valve Action intake, compression, power, and exhaust to occur (fig. 8). The four
events do not, however, depend on the piston's position in the
cylinder. Events occur because of valve action.
For example, the piston reaches the top ofits travel, or TDC,
two times during a cycle. After the piston reaches TDC, it starts
moving down the cylinder. When moving down, the piston can be
either on the intake stroke or on the power stroke.
If the intake valve is open, the piston is on the intake stroke. Air
enters the cylinder through the open intake valve. If, however, both
the intake and exhaust valves are closed, the piston is on the power
stroke. Hot compressed air has ignited the injected fuel, which
pushes the piston down with great force.
DIESEL ENGINES
Let's assume that when the cycle begins, the piston is moving up Four-Stroke Firing Details
the cylinder to rotate the crankshaft. Keep in mind that the
crankshaft rotates 360 degrees to make one complete revolution.
Intake Stroke
IS
DIESEL ENGINES
Ignition Stroke
Near the top of the compression stroke, both the intake and the
exhaust valves close. An instant before the piston reaches TDC, the
injector sprays fuel into the cylinder. The fuel enters the combus
tion chamber, spreads out, and starts to ignite just before the piston
reaches TDC. Because the fuel starts to burn just before the piston
reaches TDC, the piston is able to use the burning fuel and
expanding gases as it passes TDC and travels down the cylinder.
If the injector injected fuel at the same time the piston reached
TDC, the piston would already be moving down the cylinder by the
time ignition occurred, resulting in a considerable loss of power.
When properly timed, the injectors put fuel into the cylinder at
about ro degrees of crankshaft travel before TDC. At 10 degrees
before TDC, the piston is only about 0.005 to O.oro of an inch (in.)
orO.l 27 tOO.2 540fa millimetre (mm) from its topmost position. The
amount the crankshaft moves when the piston is near TDC or BDC
is quite large when compared to the amount the piston moves.
Power Stroke
On the power stroke, the fuel burns as expanding gases force the
piston down. The power stroke shows a major difference between
a diesel engine and a spark ignition engine. Because an SI engine
draws in fuel with intake air, compression must be low to keep the
temperature low and prevent the fuel-air mixture from igniting.
When the piston reaches TDC in an SI engine, a spark plug
ignites the fuel-air mixture. This mixture burns very rapidly,
causing an instantaneous push on the piston. Since this mixture
burns fast, the power stroke does not last long, especially when
compared to a diesel engine.
Diesel Fuel Injection One advantage of a diesel over an SI engine is that a diesel injects
a large amount of fuel. Also, diesel fuel burns more slowly, over a
longer period of time, than gas or LPG. Ignition of this large
amount of relatively slow-burning fuel causes a high-pressure rise
on top of the piston. When this slug of fuel burns, the piston
receives a very large push to begin the long power stroke.
As the piston moves down the cylinder on the power stroke, the
injectors put more fuel into the already expanding gases on top of
the piston. This additional fuel burns, expands, and causes a
continuing rise in pressure on top of the piston. As a result, a diesel
engine has a great deal of lugging power, because the fuel burns
continuously over a longer period compared to gas or LPG.
16
DIESEL ENGINES
Exhaust Stroke
The power stroke ends while the piston is still moving down the
cylinder. At about 30 degrees before BDC, the exhaust valve opens
and the exhaust stroke begins. The exhaust valve opens before
BDC to give the piston plenty of time to remove the burned
exhaust gases from the cylinder.
The piston passes BDC and moves up to force the exhaust
gases out the open exhaust valve. The exhaust valve remains open
until about 20 degrees after the piston passes TDC. Then the
intake stroke begins again. In the meantime, the intake valve
opened before the piston reached TDC on the exhaust stroke.
Both the intake and exhaust valves being open at the same time is
valve overlap.
Valve overlap allows the exhaust gases to escape completely,
which ensures a clean cylinder. Overlap also allows inlet air to fill
the cylinder completely by the time the piston reaches BDc.
Moreover, valve overlap lets some of the cool incoming air mix
with the escaping hot exhaust gases. The incoming air cools the
exhaust valve to extend its life.
17
DIESEL ENGINES
ROCKER ARM
VALVE COVER
COMBUSTION
/ PUSH ROD
CUP
AIR INTAKE PASSAGEWAY
MANIFOLD
VALVE
PISTON
CAMSHAFT
CRANKSHAFT
COUNTERWEIGHT
SCREEN ~~~~~1I1
18
DIESEL ENGINES
On top ofthe valve cover in figure 9is abreather (also tem1ed abreather Breather Cap and rcv
cap). Air, as it expands or contracts with changes in temperature, Valve
moves in or outofthevalve cover and crankcase through the breather.
The crankcase is the lower body of the engine, which houses the
crankshaft. The valve cover is a metal shroud bolted over the valves
that protects the valves and keeps lubricating oil from escaping. The
breather also vents blow-by. Bkrw-by is high-pressure combustion gas
that escapes between the piston and cylinder. Byventing blow-by, the
breather prevents a buildup of crankcase pressure.
Many engines have positive crankcase ventilation (FeY) valves
(not shown in the illustration) installed between the breather and
the air-intake manifold. A manifold is a series of connected pipes
through which substances such as air, water, or other fl~ids flow.
Usually, a manifold serves to join several pipes into one main pipe.
The air-intake manifold is the piping through which the engine
draws intake air into the cylinders. pev valves direct blow-by to
the intake manifold, where the pistons draw it into the cylinders for
recycling. pev valves cut down on air pollution. They also remove
corrosive fumes from the crankcase and prevent sludge formation.
Some engines have a cvmbustirm cup in the combustion chamber (see Combustion Cup
fig. 9)' The precombustion chamber houses the injector. Not all
diesels have combustion cups, but on those that do, the air heated by
compression accumulates in this chamber. When the injector shoots
diesel fuel into the chamber, ignition takes place. The expandinggases
travel down the passage from the cup to the top of the piston.
The illustrated engine's injector is a spray nozzle that breaks diesel Fuel Injector
fuel into a large number of tiny droplets in a process called
atomizing. Air surrounds these droplets so they can easily ignite. A
spray nozzle contains a spring-loaded plunger, which is a steel rod,
or shaft, that moves up and down in the injector to supply fuel to
the spray nozzle.
Many devices are available for delivering fuel to an engine's
injectors. In figure 9, a distributor injection pump delivers fuel to
each injector. This fuel distributor is similar to the electrical
distributor on an automobile engine. Instead ofsending electricity
to several spark plugs, however, the fuel distributor uses precision
timing to send fuel to several injectors.
DIESEL ENGINES
To summarize
Four-strokcjlring C)tc/e
• I st stroke, down-air intake
• 2nd stroke, up-compression
• 3rd stroke, down-power
• 4th stroke, up-exhaust
• On the compression stroke, the piston compresses the air in
the cylinder so much that it reaches l,ooo°F (S40°C).
• On the ignition stroke, the fuel injector sprays fuel into the
cylinder, where it ignites because of the very hot air.
20
DIESEL ENGINES
SUPERCHARGER INJECTOR
(BLOWER)
EXHAUST VALVE
AIR
INTAKE COMPRESSION
POWER EXHAUST
In a two-stroke engine, a power stroke occurs each time the piston Two-Stroke Power
reaches TDC. It therefore theoretically produces almost twice the
power of a four-stroke engine. Further, a two-stroke engine
quickly responds to throttle changes. It also weighs less per
horsepower than a four-stroke engine. In spite of the differences
between a two-stroke and a four-stroke engine, however, engine
choice depends largely on the buyer's preference.
21
DIESEL ENGINES
ConcuffentEven~in A two-stroke engine fires every time the piston reaches TDC.
Two-Stroke Engines Thus, several things happen at once. For example, intake and
exhaust occur at the same time, and the power stroke occurs every
time the piston moves down the cylinder.
Power, Exhaust, and Manufacturers must use forced-air induction on a two-stroke diesel.
Intake Stroke To see why, first think of the piston going down the cylinder on the
power stroke. Just before the piston tmcovers the intake ports in the
cylinder wall, the exhaust valves at the top of the cylinder open. The
open exhaust valves release pressure inside the cylinder.
At BDC, the piston uncovers the intake ports. The piston
cannot, however, draw in air because it is at BDC and has momen
tarily stopped moving. The intake air, therefore, has to be under
pressure to get into the cylinder. So once the piston uncovers the
intake ports, the engine-driven blower forces air through the
cylinder. This air fills the cylinder and pushes the burned exhaust
gases through the still-open exhaust valves.
The amount of exhaust gases the fresh air forces into the
engine's exhaust manifold is measured in terms of scavenging
efficiency. A two-stroke engine should have about 98 percent scav
enging efficiency. That is, intake air should move about 98 percent
of the exhaust gases out of the cylinder.
Compression and Power With the cylinder full offresh air, the piston moves up the cylinder
Stroke on the compression stroke. Before the piston completely covers the
inlet ports, the exhaust valves close. When the piston covers the
ports, compression takes place. With the piston near TDC, the
injectors supply fuel, and the power stroke begins as the piston
starts down.
Cutaway ofa Two-Stroke Figure I I is a cross section ofa two-stroke-per-cycle diesel engine.
Diesel The manufacturer arranged this engine's pistons and cylinders in
a V-shape. Several cylinders make up each side of the V.
The drawing shows the fuel-injection system and the ports in
the cylinder wall on the left. It also shows the exhaust valves and a
cutaway of the piston in the cylinder on the right. In this engine,
each fuel injector contains a high-pressure plunger pump operated
by a cam and a rocker arm. This type of injector does not require
a separate fuel-injection pump.
22
DIESEL ENGINES
CAMSHAFT CAMSHAFT
EXHAUST
ROCKER ARM
FUEL
METERING
RACK
HIGH-PRESSURE
INJECTOR PUMP ~W~~
GLOW PLUG
CYLINDER
SCAVENGING
PORTS
PISTON ROD
WATER
LINE
OIL SPRAY
NOZZLE
LUBRICATING
OIL PAN
the other end goes down and pushes against the pump plunger to
operate it. V\Then the high point of the cam rotates away from its
end of the rocker arm, the rocker arm spring pushes its end up and
the pump plunger closes.
As shown on the right side of figure cams and rocker arms also
I I,
operate the exhaust valves. The cam lifts one end ofthe rocker arm,
causing the other end to press down on the exhaust-valve stems.
This action opens the exhaust valves. When the high point of the
cam rotates off the rocker arm, the spring-loaded valves close.
To summarize
High-speed engines require diesel fuel with a spec.ific gravity of Specific Gravity and
about 0.82 to 0.89 (410 to 27 0API). Other diesel engines can use API Gravity
fuel with a specific gravity of about 0.9 I (24 0API). Specific gravity
is the ratio of the weight of one volume ofliquid (diesel oil, in this
case) to the weight ofan equal volume ofwater. Water has aspecific
gravity of I. Thus, a fuel with a specific gravity ofless than I weighs
less than water.
Many years ago, the oil industry established API gravity as a
density measure for oil and oil products. API gravity is given in
degrees API (for American Petroleum Institute). The API sets stan
dards, recommends practices, and issues bulletins on all phases of
the oil industry.
Two equations s.how the relation between API gravity and
specific gravity-
APIgravity = (I41.5+specificgravity)-J3I.5 (Eq.I)
Specific gravity = 141.5 + (API gravity + 131.5) (Eq.2)
For example, suppose you had a diesel fuel with a specific gravity
of 0.88. What is this fuel's API gravity? The following equation
gives the answer:
API gravity = (141.5 + 0.88) - 131.5
= 160.8-131.5
API gravity = 29.3 degrees
DIESEL ENGINES
On the other hand, if you had a fuel with an API gravity of 38.2
degrees, its specific gravity would be calculated as follows:
Specific gravity = 141.5 -;- (38.2 + 131.5)
J4 J ·5 -;- 16 9.7
=
Specific gravity = 0.834
Note that the lower a liquid's specific gravity, the higher its API
gravity. Thus a lightweight liquid has a low value for specific
gravity and a high value for API gravity.
Fuel Quality The quality of the fuel a diesel engine burns makes a difference in
how well itruns. Itis therefore importantto know the quality ofthe
fuel. Properties that affect a fuel's quality include
• volatility,
• amount of carbon residue,
• viscosity,
• sulfur content,
• ash, sediment, and water content,
• flash point,
• pour point,
• acid corrosiveness, and
• ignition quality and cetane number.
Carbon residue is the carbon left after a fuel evaporates. Labora Amount of Gtrbon
tory technicians find how much carbon residue is in a fuel by Residue
heating it until the volatile part of the fuel completely evaporates.
The amount ofcarbon residue indicates how much carbon the fuel
will deposit on an engine's parts. Too much carbon can make an
engine run inefficiently: its fuel consumption goes up, the carbon
creates hot spots that cause problems, and the engine may not run
well. Maximum allowable carbon residue in fuels is 0.1 percent.
Sulfur in diesel fuel burns to produce corrosive gases. When an Sulfur Content
engine operates under a light load, its operating temperature
drops. At the lower temperature, corrosive gases in the cylinder
turn to liquid. This liquid is very corrosive to engine parts,
especially the exhaust system. Thus, corroded exhaust-system
parts may show that a problem exists with other parts as well. To
reduce such corrosion, fuel specifications limit sulfur content to
0.5 percent.
DIESEL ENGINES
Ash, Sediment, and Ash, sediment, and \\·ater in a fuel can create problems. Ash and
Water Content sediment are abrasive and quickly wear out the engine. Sediment
may clog the fuel system. \Vater, especially salt water, in a fuel
corrodes engine parts and accelerates wear. Maximum permissible
ash content is 0.01 percent. Maximum permissible water-and
sediment content is 0.05 percent.
Flash Point The flash point of a fuel is the temperature to which the fuel must
be heated to give off enough flammable vapors to flash (momen
tarily ignite) when touched by a flame. Afuel with a low flash point,
such as gasoline, is dangerous to store and handle. It gives off
enough flammable vapors to flash at a low temperature-at or
below nonnal room temperature. Specifications state that the flash
point for diesel fuel can beno lowerthan 1so°F (6S.6°C). This flash
point indicates that the fuel must be heated to 150°F (6S.6°C)
before it gives off enough vapors to flash.
Pour Point The pourpoint is the temperature at which a diesel fuel thickens and
ceases ·to flow. At or below a fuel's pour point, you cannot easily
pour the fuel out of a container; it is like gelatin. Also, you cannot
easily pump a fuel at temperatures below its pour point. The
maximum pour point for diesel fuel is o°F (-17.8°C).
The pour point affects the engine's start-up in cold weather.
When fuel reaches a temperature below its pour point, it cannot
flow through fuel lines. As a result, the engine cannot start. The
engine operator must consider the pour point ofa fuel when storing
it for transfer to the engine. Temperatures at or below the pour
point prevent the fuel from flowing from the storage tank to the
engme.
Acid Corrosiveness The acid corrosiveness factor indicates the amount of acids in a fuel
that cause corrosion. Refiners must keep the amount of acids low.
Otherwise acids can damage metal surfaces both in a storage tank
and in the engine. As long as rig operators purchase their diesel fuel
from reputable suppliers, they usually do not have to worry about
acid levels being too high. Reputable refingers and suppliers strive
to keep acids in fuel at very low levels.
28
DIESEL FUEL
Cetane Number
One measure ofignition quality is a fuel's mane number. The cetane
number is tl1e percentage ofcetane in a mixture ofcetane and alpha
methyl-naphthalene. Cetane and alpha-methyl-naphtl1alene are hy
drocarbons produced from tar oil. (A hydrocarbon is a substance made
ofhydrogen and carbon.) Cetane has excellent ignition quality, while
alpha-methyl-naphthalene has poor ignition quality. A laboratory
tests a diesel fuel's ignition quality by comparing it to the ignition
quality of a mixture of cerane and alpha-methyl-napthalene.
The ignition quality scale nms from 0 to 100. Pure alpha-methyl
naphthalene corresponds to 0. Pure cetane corresponds to 100. Afuel
with acetane number of48, for example, has the same ignition quality
as a mixture of 48 percent cetane and 52 percent alpha-methyl
naphthalene. High-speed diesel engines require fuel with a cerane
number of about 50.
Effects of A diesel fuel that fails to meet specifications may harm the engine
Unsatisfactory Fuel or reduce its efficiency. For example, using a fuel with
• low volatility reduces the maximum power output, increases
fuel consumption, gives a smoky exhaust, and makes cold
starting difficult.
• high carbon residue deposits carbon and gummy substances
on pistons and cylinder liners. Such deposits may cause the
piston rings and valves to stick.
• too high a viscosity may cause a smoky exhaust, excessive
wear on injection-pump plungers and barrels, pump leak
age, and contamination of crankcase oil by fuel oil.
• too much sulfur, ash, and sediment causes excessive wear on
pistons, piston rings, liners, and fuel-injection equipment.
• too high a pour point may make it difficult to start a cold
engme.
• too many corrosive acid components causes rapid wear on
engine parts.
• poor ignition quality, or a low cetane number, makes it hard
to start high-speed engines. In addition, poor ignition qual
ity causes rough, noisy operation.
3°
DIESEL FUEL
To summarize-
Dieselfuel
• Properties that affect a fuel's quality include volatility;
carbon-residue amount; viscosity; sulfur content; ash, sedi
ment, and water content; flash point; pour point; acid
corrosiveness; and ignition quality.
• Volatility should be high for small, cool-running diesels.
• Carbon-residue amount should be no more than 0.1 per
cent.
• Viscosity should be proper for the engine.
• Sulfur content should be no higher than 0.5 percent.
• Ash, sediment, and water content should be within the
maximum limits of 0.01 percent for ash, and 0.05 percent
for sediment and water. .
• Flash point can be no lower than 150°F (6S.6°C).
• Maximum pour point is o°F (-I7-8°C).
• Acid amounts should be low.
• Ignition quality is measured by the cetane immber-about
50 for high-speed diesel engines.
31
DIESEL ENGINES
Fuel Supply Rig desig11ers can vary the la~'out of the system th8t supplies diesel
Systems fuel to an engine's fuel-injector valves. All systems, however, share
some common features, such as fuel-supply tanks, strainers, filters,
supply lines, pumps, and injector v,llres (fig. 13).
System Using Separate The fuel supply system in figure 13 is for a diesel engine whose fuel
Injection Pump and Day injector valves require a separate injection pump. Sume injectors
Tank have a built-in pump and others use a distributor-type pump.
The illustrated system has a main supply tank, a day tank, and
several fuel strainers and filters. It also has a transfer pump between
the main supply tank and the day tank. (Some supply systems do not
need this pump.) The system also has a primary enginc fuel pump.
INJECTOR RETURN
DELIVERY
LINE
VENT
SHUTOFF
\-ItI"""'It--++-.- DRAIN
SAFETY
SHUTDOWN
Main Tanks and Day The main supply tank holds a lot offuel. Either the force ofgravity
Tanks or a transfer pump moves it to the day tank. Typically, a day tank
holds enough fuel to run an engine for several hours. The day tank
thus supplies the immediate fuel needs of the engine.
DIESEL FUEL
On land rigs, which frequently move from site to site, the rig
up crew sets up the engines anu sm;~ll day tanks first. They then fill
the day tanks with fuel, start the engines, amI use this powerto erect
the rest of the rig. The crew finally sets the main supply tanks,
which provide fuel for the day tanks during regular operations.
Offshore, where it is not necessary to disassemhle rig compo
nents for moves as it is on land, the rig usually does not need day
t'mks. Main supply tanks alone provide engine fuel.
On rigs where builders can install the main supply tank above the Pumps Versus Gravity
day tank, they do not need to install a fuel transfer pump. With the
main tank above the day tank, gravity moves the fuel.
In the system in figure 13, each fuel-injector valve has its own built System with Built-In
in pump. Built-iIl'pumps eliminate the need for a remote injector Pumps
pump. The system consists ofasupply tank, a primary fuel strainer,
a fuel pump, a secondary fuel filter, and fuel lines to the injectors.
The gear-type fuel pump transfers fuel from the supply tank to the . Fuel Pump
injectors. The injectors do not require that fuel be delivered to
them under high pressure. Injector pumps need only moderate
pressure to work. The fuel system therefore does not need high
pressure lines or fittings.
The pump circulates more fuel through the injectors than they Excess Fuel
need to spray into the engine. Circulating excess fuel purges
(removes) air from the system. Removing air prevents vapor lock
when the engine runs on lightweight fuel. Vapor lock occurs when
the liquid fuel vaporizes and forms gas bubbles in the fuel system.
These bubbles keep the fuel from flowing. The excess fuel also fills,
lubricates, and cools the injectors. Aline from the injectors returns
fuel to the supply tank.
33
01 ESEL ENGINES
Fuel Tank Vents Referring again to figure 13, note the vents on all the fuel tanks,
including the main supply tank. In the fuel system diagrammed in
figure 14, the tank h3s avent pipe and avented cap. Vents allow air
to flow into the tanks as they empty or fill. When draining a tank,
letting in air keeps the tank from collapsing. As the fuel rushes out
of the tank, it creates a vacuum (an area of low pressure). If air
cannot rush in at the same time to replace the fuel, the higher
atmospheric pressure outside the tank could crush it.
FUEL MANIFOLDS OR
CONNECTIONS AT CYLINDER HEAD
RESTRICTED FITTING
CHECK VALVE
(optional)
FUEL
PUMP
VENTED
FUEL CAP
SECONDARY REMOVABLE TANK VENT
FILTER SCREEN PIPE FUEL
EXPANSION PRIMARY
VOLUME (1 Y2% STRAINER
of total vOlume~
~~~I~~=t=~
t
TOTAL
t
USEFUL FUEL
VOLUME VOLUME TANK
t -l-
CONDENSATION
VOLUME
1
(5% of useful
volume)
DRAIN VALVE
Figure 14. Fuel system showing vented fuel tank, straine'r, filter,
pump, and injectors
34
DIESEL FUEL
Figure 14 compares the fuel tank's total volume with its useful Total Volume and Useful
volume. Useful volume allows room in the tank for condensate Volume
water, which comes from water vapor in the air above the fuel in the
tank. The water vapor condenses into liquid water with tempera
ture changes. (Water condensation is like morning dew on a lawn.
In the morning, when the temperature drops, the water vapor in
the air condenses on the· grass as dew.) In a fuel tank, condensate
water settles to the bottom. The fuel system withdraws only the
fuel above the water.
Useful volume also allows room for the fuel to expand when the
temperature rises. In figure 14, the expansion volume is shown to
be I Yz percent of the total volume, while the condensation volume
is 5 percent of the total.
Since water is an enemy ofthe diesel engine, operators always keep Fuel Handling Tip
the tank that feeds fuel to the engine as full as possible, being
careful, though, to allow for expansion. Low fuel levels leave too
much room for water vapor on top of the fuel.
In figure 13, note the position ofthe deliveryline from the main supply Delivery Line Location
tank to the day tank, exiting the main tank at a point higher than the
lowestpointin the tank. This arrangementprevents condensatewater
from being withdrawn with the fuel in the delivery line. The water
settles to the lowest point, where personnel can draw it offthrough the
drain. The shutoffvalve stops fuel flow and allows amechanic to work
on the strainer and the transfer pump.
35
DIESEL ENGINES
Filters, Strainers, and Filters and strainers remove foreign p;lrtic.les in fuel that cause engine
Centrifuges wear. Filters also keep condens,lte \,rater trom entering the engine
where it could cause hann, Manufacturers provide stainless steel
strainers because brass or copper currodes in fuel oil.
The strainer on the fill-up line between the main tank and the day
tank is usually a 20- to 50-mesh stainless steel screen, which catches
any trash that may have gotten into the line, Screen-mesh numbers
indicate the number ofopenings in aline;lr in. (2 5-4mm) ofthe screen
material.
For instance, asquare in. (in. 2), or asquare 25-4 mm (mm 2) of 20
mesh screen has 20 openings along each edge. Thus, there arc 400
openings (20 X20) per in. 2 (per 25.4 mm 2). Regardless ofthe number
ofopenings in ascreen, the screens should be removed and cleaned in
kerosene or other suitable solvent at scheduled times.
Although figure 13 shows asingle fuel line for ease ohmderstand
ing, rig owners usually install two or more strainers and filters in
parallel between the main tank and day tank. In figure 13, the strainers
and filters are in aseries, one after the other in the same line. Installing
them in parallel means running two or more lines beside each other
(parallel to each other) and installing filters and strainers in each ofthe
parallel lines. Moving fuel through asingle line with strainers or filters
in series restricts the volume offlow. Thus, asystem with only asingle
strainer or filter line takes too much time to fill the day tank.
Metal-Edge Strainers
Some engine operators prefer metal-edge strainers because they are
rigid and resist damage. Ametal-edge strainer consists ofa stack of
thick, round, perforated disks separated by thin metal spacers.
Each spacer's thickness is 0.0003 in. (0.0076 mm). Assembled on a
hexagonal rod, the disks form a cylinder that is placed in a housing.
This strainer stops particles thicker than 0.0003 in. (0.0076 mm)
the distance between the disks-against the outside surface of the
assembled disks.
Over time, a layer of sludge and din· accumulates on the outer
surface of the str(jjner disks. This accumulation improves the effec
tiveness of the filter; however, it also increases the flow resistance.
Scheduled maintenance is therefore necessary to remove such accu
mulations, using the built-in cleaning device. This device is a fixed
square rod with cleaning blades. Turning a handle on the strainer's
hexagonal rod rotates the disks, and the ends of the stationary blades
scrape offthe accumulated sludge and dirt. The dirt falls to the bottom
of the strainer housing and is removed through a drain.
DIESEL fUEL
Tank Filters
Figure 15 shows four tank filters. All have bypass vaJycs that allow
fuel to f10\~ around the filter if it becomes clogged. Filters must be
cleaned regularly to prevent clogging. If the elements are dispos
able, they should be replaced regularly, disposing of used filters in
accordance with onsite environmental regulations.
STANDARD DESIGN
STANDARD DESIGN
Four Element
(With External Bypass Valve)
(With Internal Bypass Valve)
B,"g Filters
. \ hag filter is a woolen small-mesh bag equipped with helical
springs that hold it in the shape of a cylinder. The cylindrical
<,urface increases the filtering area, reduces the fuel's velocity, and
filters we]] with only a small drop in pressure. The bag may be
cleaned by taking it out and washing it in kerosene or another
<'uitable solvent
2. trap water,
•••••
• • ••
•• •
•••
•••
-.• •••
••• 1Il"'('-3----!- PERFORATED
CAN
•••• ••
••
• •••
•••
••
MICROPORE
PAPER
• ••
•• • •
••
•••
•• • •
•••••
......
...
'
• • ~
••
••• •
...•••••
Figure 17. Disposable fuel
filter made ofmicropore
paper
DIESEL ENGINES
Many rig owncrs employ spin-on fuel filters (fig. 18), which
resemble the oil filter on an automobile but are quite different in
design. So, do not use an auto oil filter as a spin-on fuel filter. Rigs
require specially designed spin-on filters, which must be replaced
regularly, using all necessary environmental precautions. A built
in gasket ensures a good seal between the filter and the engine's
receptacle.
BUILT·IN GASKET
SEALED
ENDPLATES
THICK STEEL
SHELL
HIGH STRENGTH
HEAVY STEEL
FILTER PAPERS
Water Separators
An engine operator should not transfer contaminated fuel into the
day tank. Dirt and water in the engine's day tank can quickly
overload the filters and plug fuel lines.
One method ofdecontaminating fuel is touse awaterseparator
and a fuel filter. Rig owners usually place the filter between the
main tank and the pump that transfers fuel to the day tank. One
type of water separator is a fuel centrifuge, usually placed between
the day tank and the main tank.
The centrifuge spins fuel at a very high speed. As it spins,
centrifugal force separates out the particles ofdirt and water, which
are heavier than fuel. Centrifugal force magni fies the differences in
weight between the fuel and the dirt and the water. Centrifugal
separation is faster than gravity separation, in which the fuel simply
sits until the heavier materials fall out of it.
Transfer Pumps
A rig's layout determines whether fuel-transfel' pumps need to be
installed. If the builders cannot install the day tanks above the
engine's fuel injectors or fuel-injector pumps, the force of gravity
cannot deliver fuel to them. In such cases, the rig owner installs
fuel-transfer pumps, usually powered by the engine, between the
day tank and the engine. ' r0 keep from having to shut down the
engine to work on a transfer pump, hand- or motor-operated
auxiliary transfer pumps are installed.
Pump Sizing The amount offuel the main tank and the day tank hold determines
the size ofthe pumps needed to transfer fuel from storage. Most rig
owners require that it take no longer than 30 minutes (min) to fill
a day tank. If, therefore, an engine has a 45o-gallon (gal) or a 1. 7-m3
day tank, the transfer pumps must deliver 15 gal per min (gpm)
because 450 gal + 30 min = 15 gpm. (This rate is about 0.06 m 3/min
because 1.7 m3 + 30 min =about 0.06 m 3Imin.) If the engines have
two or more day tanks, the pump may have to be large enough to
fill more than one tank at a time.
Pump Location If the main storage tanks are below engine-room level or below the
day tanks, the transfer pumps should be located at the same level as
the main storage tanks. Keeping the pumps at the same level as the
main tanks ensures that the pumps stay primed (full of fuel).
Locating the pumps at the same height as the main tanks is
especially important for centrifugal pumps. Centrifugal pumps
cannot lift fuel higher than 20 feet (ft) or 6metres (m). On the other
hand, if the rig uses rotary pumps their location is not as criticaL A
centrifugal pump has rotating elements like gears or lobes. Two
sets of gears or lobes rotate and intermesh within a pump housing.
The intermeshing gears or lobes move the fuel.
When a transfer pump is a long way from the day tank, it is
important to set the controls of the pump so that it automatically
stops after it fills the day tank. This setting cuts down on the danger
of overflow. When each day tank has its own pump, the operator
can install automatic switches operated by the tank's fuelleve!'
Fuel Lines Fuel lines are usually standard steel pipe with screw fittings. Some rig
owners use copper or brass tubing with flared fittings for high-grade
diesel oils. If the fuel contains sulfur, however, neither copper nor
brass fittings should be used, since sulfur corrodes these materials.
DIESEL FUEL
Paraffin
Some fuel oils contain paraffin. Paraffin is liquid at high tempera
tures. At low temperatures, however, it is a solid wax. In cool
weather, it may drop out of the fuel and stick to the wall of the fuel
line. Most engine operators, therefore, use plugged tees, instead of
elbows, at all bends in the line. By removing the plug from the tee,
personnel can clean paraffin from the lines.
43
DIESEL ENGINES
Connections
AJI fnelline connections coming off the suction side of the pump
must be constantly checked to make sure they are tight. Tight
connections keep air from entering the line.
Flexible Hoses
Some rig owners use flexible hoses for fuel lines. Flexible hoses do
not break or come ap<lrt because of engine vibration. S~·nthetic
rubber hoses reinforced with braided steel should always be used,
because diesel fuel eats up natural nlbber.
Fuel Return Lines Most diesel fuel systems have return lines from the injectors hack
to the fuel tanks. These lines recover excess fuel that the system
does not inject into the cylinders. Usually, the lines take the excess
fuel to the day tanks. This is because the day tanks are usually closer
to the engines than the main fuel tanks.
Aday tank should never be set more than 6V2 ft (2 m) below the
engine's primary pump. If the tank is lower, the transfer pump has
to develop a lot of suction to lift the fuel. The pump may develop
so much suction that a vacuum may be created, causing vapor lock
and shutting off fuel flow.
Primary Pump and Some systems have an engine-driven primary pump, which supplies
Injector Pump fuel to an injector pump. It also has a lever for manual operation.
This primary (booster) pump must supply fuel to the injector pump
at 10 to 30 psi (70 to 210 kPa) of pressure. Otherwise, the injector
pump will not operate properly.
Starting an Engine To start an engine, the booster (priming) pump is worked by hand
until fuel reaches each injector and bleeds through the injector
bleed-off valve. The bleed-off valve opens to let excess fuel drain
back to the fuel tank. The bleeding process must continue until all
air is expelled from the fueIlines and filters. Air can keep the engine
from starting. Even if the engine does start with air in the lines, air
knocking can occur.
44
DIESEL FUEL
Air should enter the cylinder only through the intake valve or port. Ai r Knocking
If the injector sprays air and fuel into the cylinder, instead of just
fuel, then the cylinder may misfire, or ignite improperly. Air
knocking is a hammering noise that occurs when the injector sprays
a combination ofair and fuel into the cylinder. This trapped air can
sometimes be removed by crankjng the engine with the starter. If
this method fails, the booster pump may be manually operated
until it pumps out all the air.
If the engine continues to knock or hammer after such a pumping Removing Air
operation, it must be stopped. The booster pumping operation
should be repeated until all air is removed from the fuel. Persistent
knockjng must be attended to; either there is still air in the system,
or there is another problem. It is important to remember in any
case that diesel fuel lubricates the fuel system. Therefore, if you
operate the system with air in the fuel, it may not lubricate the
injector pump enough. A damaged pump can be the result.
To summarize-
Fuel supply systems
• Systems consist of fuel-supply tanks, strainers, filters, sup
ply lines, pumps, and injector valves.
T
T
45
Fuel-Injection
Systems
T
T
T
To obtain accurate fuel metering, the injection system must Accurate Fuel
• sense the correct amount offuel to inject for the engine load, Metering
and
• inject the same amount of fuel into each cylinder's combus
tion chamber.
If the system fails in either of these two tasks, the engine will not
run correctly.
Injecting fuel at precisely the right moment in tlle engine's oper Proper Injection
ating cycle is vital. Proper timing gives maximum power from the Timing
fuel, good fuel economy, and clean combustion.
47
DIESEL ENGINES
Fuel-Injection Rate The fuel injection rate is the quantity offuel the system injects into
the combustion chamber during one degree of crankshaft travel.
The fuel-injection rate depends on
• the amount of fuel injected, and
• the length of time (the duration) of the injection.
If the amount of injected fuel decreases, the injection duration
must increase. Conversely, if the injection amount increases, the
injection duration must decrease. If the injection amount and
injection duration do not balance each other, the engine cannot put
out consistent power.
Fuel Atomization Fuel atomization is the breakjng up of the fuel stream into a spray
of tiny droplets that mix easily with the air in the combustion
chamber. Proper atomization ensures that enough oxygen sur
rounds each small fuel particle for combustion to occur readily.
The shape of the chamber determines the type of atomization.
Some chambers require a very fine spray, whereas others operate
with a fairly coarse spray.
Good Fuel Good fuel distribution is obtained when the injectors spray the fuel
Distdbution to all parts of the combustion chamber, where oxygen is available
for combustion.
Types of Injection Engine suppliers provide four kinds of mechanical injection sys
Systems tems for diesels:
I. multipump injectors,
2. unit fuel injectors,
BARREL PLUNGER
49
DIESEL ENGINES
One Pump on Each Big engines sometimes hayc one pump mounted on each cylinder.
Cylinder Figure 21, for instance. shoyvs one side eJch of two brge V-12
diesels. Each of these engines h;lS a total of twelve pumps.
High-pressure fuel lines carry fuel frum each pump to injector
valve ;md spray-nozzle assemblies on c<lCh cylinder. Cams inside
the engine operate the pump plullg-ers as well as the engine's intake
and exhaust valves. A primary pump (nut visible in figure 2 I)
supplies fuel to the plunger pumps.
Figure 2 I. Multipump injeLtioll sy.ftem witb individual pumps plllced next to eacb qlindcr
5°
FUEL-INlECflON SYSTEMS
Acutaway ofa cam-operated multipump injection system (fig. 22) How Cam-Operated
shows parts of two pumps in a single housing. Note the fuel Plunger Pumps Work
passage. Fuel, under low pressure, flows through the passage to the
individual plunger pumps in the housing. The camshaft of the
fuel injector is at bottom. The cam contacts a lifter, which
connects to the plunger. A spring fits into the grooves on the
plunger. (It is removed in the figure to clearly show the plunger.)
PLUNGER
PUMP2
GROOVE
FOR SPRING
PLUNGER
LIFTER
CT
DIESEL ENGINES
The high point on the cam raises the lifter, which, in turn, raises the
plunger. When the cam's high point rotates offthe lifter, the spring
causes the lifter to go down, which lowers the plunger. The
movement of the plunger pumps fuel into the injector.
A cutaway that isolates a single fuel pump (fig. 23) shows the
plunger, the barrel, and the rack, which is part ofa rack-and-pinion
gear. Arack-and-pinion gear consists ofa geared, or toothed, bar
the rack-whose teeth mesh with a geared, or toothed, disk-the
pinion. Back-and-forth movement of the rack rotates the pinion.
Mechanical linkage connects the rack to a governor, which may be
installed some distance away.
A governor
• limits the maximum speed of the engine,
• increases the amount of fuel injected when the driller loads
the engine, and
• cuts off fuel to stop the engine.
The engine governor controls the position of the injector
pump rack. The rack, in turn, controls the fuel output for each
stroke of the pump plunger.
PLUNGER
BARREL
injector unit
FUEL-INJEGION SYSTEMS
- - - - PINION
53
DIESEL ENGINES
PLUNGER
-t---L1FTER
-t--CAM
54
FUEL-INJECflON SYSTEMS
Note the spring on the lifter below the plunger. This spring
forces the lifter and plunger down when the high point of the cam
rotates away from the lifter. At top left, you can see the fuel passage
into the pump, and fuel, flowing to the top of the plunger through
an inlet port.
Figure 26 shows the operation of the pump plunger in detail.
Figure 26a shows the plunger at its lowest position in the barrel.
Fuel enters the port at left and fills the chamber above the plunger.
Fuel also flows down the vertical passage in the plunger (the half
moon-shaped notch) and fills the recess.
In figure 26b, the plunger has moved up, covering the inlet
port. It traps fuel in the chamber above the plunger and forces it out
the top opening and into the fuel line.
In figure 26c, the plunger is at its highest position. Here, it
uncovers the inlet port and allows fuel trapped in the recessed area
to return to the fuel inlet. Keep in mind that the inlet fuel is under
a lot lower pressure than the fuel on top of the plunger. This lower
pressure allows fuel to return to the fuel inlet. When fuel returns
to the inlet, no more fuel passes through the outlet at top, and fuel
injection stops.
RECESSED
AREA IN
~l--+- PLUNGER PLUNGER
55
DIESEL ENGINES
In figure 26c, note that the top of the recessed area of the
plunger is beveled, or cut on a slant. The position of the beveled
recess determines how much fuel returns to the fuel inlet. The
amount of fuel that returns to the inlet determines how much fuel
can go to the engine cylinders.
As an example, when the engine load goes down, the engine
needs less fuel to maintain speed. To keep the engine from
speeding up, the governor makes the rack rotate the bevel clock
wise. Clockwise rotation enlarges the space between the bevel's
edge and the port's edge (see fig. 26c). Thus, more fuel returns to
the fuel inlet. The plunger, therefore, has less fuel to pump to the
injector valve. As a result, the engine's speed does not increase.
On the other hand, when the engine load goes up, the engine
needs more fuel to maintain speed. To keep the engine from
slowing down, the governor makes the rack rotate the bevel
counterclockwise. Counterclockwise rotation shrinks the space
between the bevel's edge and port's edge so that less fuel returns to
the fuel inlet. The plunger therefore has more fuel to pump to the
injector valve. As a result, the engine's speed does not decrease.
Once the plunger delivers fuel to the injector valve, it returns
to its lowest position and the process starts again. The governor
moves the rack to rotate the plunger as the engine requires more
or less fuel. Engine operators set the governor to perform as
required.
Injection Lines
The pump plungers send fuel through heavy steel tubing-injec
tion lines-to the fuel-injection valves and spray nozzles on each
cylinder. That is, lines farthest from the cylinder determine the
length of all the lines. Thus, a line running from a cylinder that is
close to the injector is cut to be as long as the line farthest from the
cylinder. Having injection lines the same length ensures that each
plunger pumps the same amount of fuel to each cylinder.
FUEL-INJECTION SYSTEMS
Injector Valves
A cross section of an injector valve and spray nozzle in closed
position (fig. 27) shows its parts. Injected fuel pressure on the upper
end of the valve forces the valve off its seat, allowing the nozzle to
spray fuel into the engine's combustion chamber. After injection,
the spring forces the valve closed while combustion takes place.
NOZZLE
Today, the drilling industry uses mostly unit fuel-injection sys- Unit Fuel Injection
terns for its engines. Regulatory agencies have passed stringent
emission laws, and engineers have added sophisticated electronic
controls to engine fuel systems.
Electronic control of unit injection systems offers
• precise injection timing and metering, which reduces emis
sions, and
response to problems.
57
DIESEL ENGINES
CAM
b~"-==f~- FOLLOWER
~ SPRAY
NOZZLE
FOLLOWER FOLLOWER
SPRING
FILTER CAP
STOP PIN
INJECTOR
BODY
PLUNGER
FILTER
GEAR
GEAR
RETAINER
BUSHING
SEAL
SPILL
DEFLECTOR
UPPER PORT
LOWER
PORT
CHECK VALVE
CHECK CAGE
VALVE
VALVE
SPRING CAGE
SPRING
SPRING SEAT
NEEDLE
VALVE
NUT
SPRAY TIP
59
DIESEL ENGINES
Pump Action
The action of this pump is similar to that of the multipump system.
A plunger inside the unit pumps fuel to the built-in spray nozzle.
And, as in the multipump system, the pump barrel, or bushing,
contains inlet ports that the plunger opens and closes as the rack
rotates the plunger. Rotation controls the quantity of fuel pumped
on each stroke.
Fuel Delivery
To deliver fuel, a camshaft operates a rocker ann, which contacts
the follower on the injector. The follower contacts the pump
plunger. The rocker ann pushes the follower and plunger down to
deliver fuel. To reduce or shut off fuel delivery, the rocker ann
moves away from the follower. A spring then pushes the follower
up, which allows the plunger to move up.
Control Rack
A lever linked to the engine governor actuates the control rack. A
qualified mechanic can adjust each injector lever independently,
thereby obtaining the desired setting for each cylinder.
The engine fuel pump supplies each unit injector with a continuous
flow of fuel under low pressure. Although not shown in figure 29,
the fuel-return outlet is next to the fuel inlet, which is shown.
Excess fuel passes to the fuel-return line, which directs it back to
the fuel tank. Continuous flow offuel through the injector prevents
air pockets in the system and cools the injector's parts.
Injector Operation
When the rocker ann (not shown) pushes the follower down, it
pushes the plunger down. Downward plunger movement closes
the upper and the lower ports. Continued downward movement
puts pressure on the fuel under the plunger.
This pressure opens the check valve, and fuel enters the passage
between the check valve and the spray tip. Fuel pressure forces the
needle valve offits seat, which allows fuel to flow through the small
openings in the spray tip and into the engine's combustion cham
ber. The amount of fuel pumped and the type of spray tip used on
the injector nozzle determine the engine's power.
60
FUEL-INJECTION SYSTEMS
Adistributor injection pump is 3 single pump that sends fuel under Distributor Injection
high pressure to each injector (fig. 3o).lt has a plunger into which
the manufacturer cuts a channel, or slot. The plunger rotates and
the channel distributes the fuel through an outlet to each injector.
It distributes the fuel to each injector in the proper firing order.
Firing Order
Firing order is the numerical sequence in which combustion
occurs in each engine cylinder. For example, in an eight cylinder
engine, the manufacturer may set the firing order to be 1-8-4-3
6-5-7-2. Such an order means that combustion occurs in cylinder
I first, then in 8, then in 4, and so on, until combustion occurs in
Pump Operation
The plunger rotates continuouslywhile mOvll1gup and down. Plunger
rotation and vertical movement line up ports for fuel metering and
distribution. Fuel enters the distributor through inlets not visible in
figure 30. Fuel fills the fuel sump, ports, and the cavity between the
top of the plunger and the bottom of the delivery-valve assembly.
PUMP PLUNGER
~
MOUNTING TAPPET
FLANGE RETURN
SPRING
61
DIESEL ENGINES
Intake
Beginning of Delivery
At the beginning of delivery, as shown in figure 3I, the rot<1ting
plunger mm'es up""ard, closing the fuel port and putting pressw-e
on the fuel below the deliyery valve. rl 'his pressure causes the valve
to begin opening. At this point, the channel in the plunger has
rotated to the left, or clockwise.
62
FUEL-INJEGlON SYSTEMS
Delivery
At delivery, the plunger shown in figure 3 I has moved up to close
the fuel pon, and fuel pressure has opened the delivery valve.
Arrows indicate the path of the fuel through a passage to the
plunger, through the channel in the plunger, and into the fuel
outlet. The manufacturer times the channel, or distribution slot, to
line up with the outlet to the proper cylinder in the firing sequence.
End of Delivery
At the end ofdelivery, fuel pressure forces the plunger to maximum
height. At this point, a horizontally drilled hole-a metering
hole-in the plunger rises above the fuel metering control sleeve.
The metering hole relieves pressure on the fuel. The delivery valve
.closes and the fuel escapes down the vertical hole in the plunger
and into the sump surrounding the metering control sleeve. (A
sump is simply a space or an area into which fuel drains.)
Fuel Metering
As shown in figure 3I, the position of the control sleeve controls
the quantity of fuel delivered on each stroke of the plunger. At the
end of delivery, the metering sleeve exposes the horizontally
drilled metering hole in the plunger. The center hole in the
plunger relieves pressure into the sump surrounding the metering
sleeve. Fuel delivery stops, despite continued upward movement of
the plunger.
Throttling Up
Opening the throttle and applying a load moves the metering
sleeve to midposition, as at the beginning of delivery in figure 31.
[n midposition, the metering sleeve llllCO\erS the hole in the
plunger later during the plunger stroke. This action lengthens the
effective stroke of the plunger, (lnd the injector delivers fuel for
normal operation.
HEADER
GEAR PUMP (common rail) ROCKER ARM
THROTTLE
I \ \
GOVERNOR
INJECTORS
PUSH ROD
CAM SHAFT
Fuel-Flow Control
Athrottle control regulates the fuel flow by increasing or decreas
ing the amount of fuel that enters the common rail. Increasing the
fuel flow increases pressure in the common rail, while restricting
fuel flow decreases pressure. The engine operator normally con
trols fuel flow to the rail by adjusting the throttle control lever. The
operator adjusts the throttle until the engine runs abit too fast. The
governor then reduces the fuel flow to reduce engine speed to the
desired revolutions per minute (rpm).
The throttle-and-governor system regulates fuel pressure to a
point no higher than IS0 to 250 psi (1,035 to 1,725 kPa). The
amount of pressure and the time at which the plunger opens the
injector's inlet port determine the torque and speed of the engine.
DIESEL ENGINES
To summari ze-
Fuel injection systems
• meter the fuel accurately.
• inject fuel at the correct time.
• inject fuel at the correct rate.
• atomize the fuel properly.
• distribute the fuel correctly into the engine's combustion
space.
Types ofinjection systems
• Multipump injectors have a separate high-pressure plunger
pump for each individual injector. The pumps may be
housed in one common body or individually near the corre
sponding engine cylinder.
.• Unit fuel injectors combine an internal high-pressure pump,
an injector valve, and a spray nozzle.
• Distributor injectors have a single pmnp that sends fuel
under high pressure to each injector.
• Common-rail injectors have a pump that picks up fuel from
the tank into a header, or common rail; each injector is on
the common rail.
66
Governors
INJECTOR PLUNGER
~ ..
RACK CONTROL
ON DIESEL
RACK
Figure 34. Centrifugal force moves a steel bolt on a string away from
center ofspin.
68
GOVERNORS
cause hunting.
by mechanical linkages.
Three types of governor are (I) mechanical, (2) hydraulic, and (3) Types of Governor
electrically actuated. A fourth type of governor is an overspeed
governor, which only keeps an engine from running too fast.
Manufacturers further classify governors according to their
functions.
1. Load-limiting governors limit the load an engine can take.
speed governors.
DIESEL ENGINES
I
SPEED DECREASE t:-----F--------:
SPEED INCREASE l' ~ I ~~ERLE
-......, , - - .,
~ ............ - - - - - - <
YOKE -+----lll'i.>
I
I Rt = RADIUS OF ROTATION AT
I MINIMUM SPEED
'-<llIio(,-----
I
R2 -~ =
R2 RADIUS OF ROTATION AT
MAXIMUM SPEED
7°
GOVERNORS
Adjusting a Governor
A variable-speed governor can maintain any speed within the
operating range of the engine. With spring-loaded centrifugal
governors, the engine operator can change the length of the
speeder spring.
Changing speeder spring length changes the governed speed
of the engine. A shortened spring increases the centrifugal force
required to compress the spring. The engine, therefore, has to run
faster for the flyweights to develop enough centrifugal force to
overcome the greater spring force. Conversely, a long spring
decreases the centrifugal force required to compress the spring,
causing engine speed to decrease.
DIESEL ENGINES
Two-Speed Governors
Two-speed direct-action governors use two springs in the same
assembly (fig. 36). Such governors use a soft spring for idling the
engine when centrifugal force is small and a stiff spring for higher
speeds when the engine is under load. The springs can act either
separately or together.
The advantages of mechanical governors are
• simplicity,
• small size and weight, and
• low cost.
SOFT SPRING
STIFF SPRING ~~
~/
...
- MORE
FUEL
O,.--_ _J
LESS
FUEL
;j
o
\ /
Figure 37 diagrams the operation ofa hydraulic g(JVernor. Ahydraulic HydrauliCCllly Actuated
governor is similar to a mechanical governor. The main difference Governors
is in the way a hydraulic governor regulates the spring-loaded
flyweights. In a hydraulic governor, ·the control sleeve is not
mechanically connected to the fuel-contrQI mechanism. Instead,
the control sleeve connects to apilot valve. Oil under pressure from
a pump flows to the pilot valve.
FLYWEIGHT
LESS
FUEL
MORE
FUEL
NEEDLE
•
TO SUMP
VALVE
73
DIESEL ENGINES
Variations in Speed \iVhen the engine's speed drops belm\' the set speed, the flyweights
move inward, lowering the sleeye and pilot-valve stem. Notice the
shape of the pilot valve. Its top and bottom are larger in diameter
than its middle part. \Vhen the pilot valve goes down, the large
bottom part of the valve moves away from an inlet to the power
piston. \;\Tith the inlet open, oil flows into the cylinder behind the
power piston. The oil forces the power piston to move to the right.
This movement increases fuel going to the engine and speeds it up.
vVhen the engine accelerates aboye the set speed, the fly
weights move outward. This movement raises the control sleeve
and the pilot-valve stem. The large bottom part of the valve moves
to close the inlet to the power piston. Decreasing the amount ofoil
flowing to the power piston decreases the pressure behind the
piston, '] 'he piston moves to the left and less fuel goes to the engine,
which reduces its speed.
Needle Valve
The needle valve in the line to the power piston and cylinder is a
throttling device that keeps oil from surging against the piston. A
surge causes the engine to overspeed. The governor responds to
this by slowing down the engine, often overdoing it. With the
engine going too slow, the governor then speeds up the engine.
This rapid fluctuation in speed is hunting. The needle valve
prevents hunting by preventing surges.
Compensator
Some hydraulic governors have a compensator, which prevents
hunting by anticipating the engine's return to its set speed. When
the engine goes faster than the set (control) speed, the compensator
drops the engine's rpm. Normally, operators set the compensator
to keep the drop small. With a small speed drop, the compensator
governor quickly makes the engine go back to control speed. When
the speed drops below control speed, the large power piston
quickly returns the engine to control speed (fig. 38).
Compensator governors perform well with any load changes
on the engine, from small gradual ones to large sudden ones, as long
as the changes are infrequent. Compensator governors do not,
however, work well on engines powering devices that constantly
change the load on the engine. One example is an engine driving an
alternating current (AC) generator. A compensator governor would
need constant resetting to maintain asteady engine speed and would
therefore be impractical to use in such a situation.
74
GOVERNORS
COMPENSATOR
FLYWEIGHTS
TO SUMP
75
DIESEL ENGINES
ElectriCillly Actuated An electrically actuated h)ldmll/ic gOl'C'1770T h:1s <l reversible electric
Governors motor that runs both clockwise and cOllnterclockvvise. By manipu
lating a remote control, an operator (an adiust the motor to
maintain close control of the engine's speed. Remote control j,
especially useful when the operator has to synchronize the speed of
tvro or more engines driving generators.
Figure 39 is a schematic of an electJically actmted hy,-dnmlic
governor. IJ1Stead offlyweights, this governor has <I103dingpistr )J1 that
Figure 39. Electrically works in combin<ltion with the power piston. As engine speed varies,
actuated hydraulic governor
ADJUSTABLE RESTORING
BRACKET LEVER
o
°
INCREASE
SPRING
;:..c:;:~!E-- CENTERING
LEVEL
SCREW
SPRING
TO
MAGNET ELECTRIC
CONTROL ACTUATOR
SOLENOID CENTERING
COILS SPRING
PILOT VALVE
PLUNGER
COMPENSATING
LAND
PILOT VALVE
BUSHING
LOADING
LAND
PUMP
GEAR
RELIEF
VALVE
PLUNGER
i30I HIGH PRESSURE
• CONTROL
RELIEF
PRESSURE
VALVE~>t'---lil
SPRING ~ SUPPLY OIL
Ki~~ SUMP
PUMP
GEARS
OIL SUPPLY
GOVERNORS
the pilot valve meters the oil behind the power and loading pistons to
increase or decrease the engine's speed as required. The motor in
the actuator is controlled by the driller on the rig floor.
The driller's remote control panel has a two-way switch. When
the driller tums iton, the govemor's motor adjusts the engine's speed.
When the engine reaches the desired speed, the driller rums the
switch off. The driller can tell the engine's speed by looking at a
tachometer or frequency meter on the control panel.
By holding the switch in the "lower" position, the driller can
slow the engine and even shut it down by leaving the switch
engaged. In the "rise" position, the switch increases the engine's
speed until it reaches the maximum speed setting on the govemor.
This maximum speed setting keeps the engine from going faster
even if the driller keeps the switch in the "rise" position.
Fuel Modulators
Diesel engines must meet federal and local standards on pollution.
One concern is that a diesel may produce too much smoke. If the
governor delivers more fuel than air to the engine, it is too 'rich'
and the engine smokes too much. To prevent smoking, operators
installjUel modulators in combination with a governor. The modu
lator makes the governor increase the fuel supply only at the same
rate as the air increase. Such rate control holds down the black
smoke from the engine exhaust during acceleration or sudden
loading.
77
DIESEL ENGINES
Overspeed Governors
Overspeed gm:crnon bring an engine to a full stop by cutting off
either the fuel supply or the air supply to the engine. They are
sometimes called 'trips' because they shut the engine down and
protect it from damage if overspeeding occurs. Rig owners usually
install overspeed governors along with regular governors to pre
vent engine damage if the regular governor fails. In cases where the
engine does not have a regular governor, an overspeed governor
shuts down the engine when the speed increases beyond a safe limit
before the driller can control it. Mechanical overspeed governors
operate by the centrifugal force offlyweights. Oil pressure operates
hydraulic overspeed governors, and electricity operates electrical
overspeed governors.
One type ofoverspeed governor uses a power spring to operate
the shutoff control. The installer sets the spring with a latch. If the
engine goes too fast, a spring-loaded centrifugal flyweight moves
out and trips the latch. When the latch trips, the power spring
operates the shutoff control.
To summarize
Governors
• Almost all engines have a governor that moves a rack to
regulate speed.
• Speed droop is the decrease in rpm of an engine from a no
load to a full-load condition.
• Hunting is a variation in engine speed from too fast to too
slow.
• Sensitivity is the speed change the engine makes before the
governor corrects it.
• An isochronous governor maintains the engine's rpm re
g~dless of the engine's load.
• Governor power is the force supplied by the governor to
overcome mechanical resistance in the fuel system.
• Promptness is the time it takes a governor to react to a
change in engine speed.
• Stability is a governor's ability to maintain engine speed
without hunting.
GOVERNORS
Types ofg07.'e7770TS
• Mechanically actuated
• Hydraulically ,1Ctu,Hed
• Electrically actuated
Mechanically actuated gove1710r
• Flyweights mounted on a gear-driven, rotating yoke are
brought to bear against a control sleeve which operates the
fuel-regulating mechanism. The speeder spring tries to
move the sleeve down to increase fuel, while the centrifugal
force of the rotating flyweights u"ies to move the control
sleeve up to decrease fuel.
Hydraulically actuated govenlOr
• Acontrol sleeve connects to a pilot valve; when speed drops,
the flyweights move inward to lower the sleeve and pilot
valve. When the pilot valve goes down, an inlet opens to let
hydraulic oil flow into acylinder behind a power piston. The
power piston moves to increase fuel.
• When speed goes up, the flyweights move outward to raise
the sleeve and pilot valve. When the pilot goes up, the inlet
decreases the amount of oil flowing behind the power
piston. The piston moves to decrease fuel.
Electrically actuated governor
• The engine operator adjusts a switch on a motor to control
the engine's speed. The governor has a loading piston in
combination with a power piston. As engine speed goes up
or down, a pilot valve meters the oil behind the pistons to
increase or decrease the speed.
Overspeed governors
• Overspeed governors cut off fuel or air to an engine to stop
it; they are available in mechanical, hydraulic, and electrical
verSIons.
79
Lubrication Systems
81
DIESEL ENGINES
Oil Pumps As the engine runs, it powers an oilpump. The pump is an integral pan
ofthe engine. The oil-pumping system forces cool, filtered oil through
the engine. It pumps the oil under pressure and at a fast rate of flow.
Depending on the engine's size, the oil-pumping system (fig. 40) can
circulate all the oil through the engine in a couple of minutes or less.
SUCTION LINE
FOR SCAVENGE
SCAVENGE
SECTION OF PUMP
SECTION
OF PUMP
Oil Flow Rates As an engine runs, wear occurs on its moving parts. As wear occurs, the
amount ofspace-the clearance-between the moving parts increases.
With increased clearance, there is less restriction to the flow of oil
between the parts. The oil-flow rate therefore increases, and the pump
must be able to maintain this flow-rate increase. If it cannot, the oil
pressure goes down and some pans may not get enough oil.
Relief Va/ves Most engines have a relief valve in the oil-pumping system that
maintains oil pressure as the engine parts wear. The pump moves most
of the oil to the engine parts. Part of the oil, however, returns to the
crankcase through the relief valve. If the engine is running at high
speed, alotofoil goes to the crankcase. Atintermediate and lowspeeds,
less oil goes to the crankcase. The reliefvalve keeps aconstant pressure
on the oil system whether the engine is nmning at a low, an interme
diate, or a fast speed.
As wear increases, less oil goes through the reliefvalve, regardless
ofthe engine's speed. When an engine or an oil pump becomes badly
worn, most ofthe oil goes to the engine. Asmall amount returns to the
crankcase through the reliefvalve; even so, the oil cannot do its job.
With large clearances, the pump cannot maintain enough pressure to
form a good film. When an engine's oil-pressure gauge shows low
pressure at normal operating speed, the engine or the oil pump needs
. .
major repalr.
LUBRICATION SYSTEMS
As oil circulates through an engine, it picks up dirt, small metal Oil Strainers and
particles, and other foreign material. All can damage the engine. Filters
Manufacturers put strainers and filters on most engines to clean
the oil. Strainers take out large particles, whereas filters remove
small ones.
Manufacturers place the oil pump's inlet very close to the top of Strainers
the oil in the crankcase. They also place on the inlet a strainer that
consists of a fine-mesh bronze screen. Some strainers float on the
oil's surface. The inlet and strainer are close to the top because
most foreign matter is heavier than oil and sinks to the bottom of
the crankcase. With the matter on bottom, the pump cannot pick
it up and it therefore does not circulate through the engine. Any
material that does not sink to the bottom, and is relatively large,
is caught by the oil strainer. The oil filter traps the finer particles.
Manufacturers make many sizes and shapes of oil filter, utilizing Filters
such varied materials as paper, wool, cotton, metal, and charcoal.
Most often, however, paper and cotton are the preferred filtering
elements.
It is important to replace the old oil filter with a new one of the
proper size and type. Many filters look the same on the outside but
are different on the inside. For example, a fuel filter and an oil filter
can be the same size and look the same, but not be interchangeable.
Installing a fuel filter in place of an oil filter can cause serious
problems. The small holes in the fuel filter do not allow thick oil
to flow easily. As a result, much of the oil flows around the filter,
and no filtering occurs. On the other hand, fuel passes easily
through an oil filter, but the filter's size does not stop pieces of dirt
that could harm the fuel-injection system.
DIESEL ENGINES
Importance of Filtering
Filtering is an important part of the lubrication system. Any hard
particle larger than the clearance oetween two moving parts can
wear or damage an engine. An insert bearing resting in a rod cap,
for example, is very thin-o.005 in. to 0.015 in. (0.127 mm to o. 38r
mm). If the oil carries a particle thicker than the thickness of the oil
film coating the bearing, the particle scores the bearing's surface
(fig. 41). An oil filter has to catch all such particles.
Some particles are, however, so small that they can circulate in
the engine without causing wear. If the oil filter trapped all these
tiny particles, it would quickly stop up. The engine manufacturer
therefore recommends using a filter that balances engine protec
tion against filter life. Many engines use filters that last as long as
1,000 hours, depending on the output of the oil pump, the number
of filter elements, and other factors.
ACTUAL BEARING
THICKNESS
0.005 IN. - 0.015 IN.
(0.127 MM - 0.381 MM)
GROOVE CUT
BY FOREIGN
PARTICLE
Number of Filters
,\LlIluFactlirers pnwide he;.Jv~·-dllty engines "vith two or more
flters (fig..p). A lot of oil passes through such fllters. If, for
example, ~111 engine can pump oil at 22 gal (0.08 m3) per minute,
then it pumps 1,320 gal (5 m3) every hour. If two filters ;Ire on the
engine, the filters c!e<1Il660 gal (2.5 1113) of uil per hour. So, ifthe
engine mech;lnic changes the filter elements ;lfter 125 hours, each
will have filtered 82,500 gal (over 300 nl\) of oil.
Filter Pressure Engine operators use many methods to check whether afilter is still
doing its job. One of the best is to have two pnlSltre gauges, one on
Gauges
the inlet side (\vhere oil enters the filter), and the other on the outlet
side (where oil leaves the filter). The two gauges indicate the
resistance that the filter puts on the oil flow.
The gauge on the inlet side should indicate slightly higher
pressure than the one on the outlet side. The pressure difference
should, however, be no more than 7 to IO psi (50 to 70 kPa). A 15
psi (IOO kPa) difference betv.'een the two gauges means that the
filter is clogging. 'i\'hen a filter clogs, a motorhand or mechanic
should replace it immediately.
Filter Bypass Oil filter manufacturers add a bypass (relief) valve to each filter as a
safety feature. This valve opens to let oil bypass the filter if dirt
Valves
blocks it up. Dirty oil provides better lubrication than no oil at all.
The bypass valve starts working when the filter puts up more than
about 20 psi (140 kPa) of resistance.
Oil Coolers The oil pump on most engines sends the oil through an oil cooler
before it goes to the filters. If oil gets too hot, it breaks down and
cannot lubricate. Engine manufacturers often use the engine's
coolant to cool the oil as well as the engine.
One type of oil cooler is placed near the oil-pumping system
(fig. 43)' Oil from the pump enters a line at the bottom of the cooler
body. The line coils arOlmd inside the cooler body and exits from the
side. The coolant enters the top of the cooler body; it also exits from
COOLANT
COOLANT ENTRANCE
OUTLET
PRESSURE
LINE FROM
THE OIL
PUMP
FilfUre 43· Placement of
an oil cooler in lubrication
system
86
LUBRJCATION SYSTEMS
the top but from another side. As the hot oil in the oil line contacts the
lower-temperature coolant in the cooler body, some ofthe heat in the
oil goes to the coolant, which carries the heat 3W3r from the oil.
On some engines, the manufacturer installs 3 bypass system with Oil Cooler Bypass
the oil cooler (fig. 44)' "\Then the engine is cold and the oil is thick
System
(viscous), it cannot flow easily. To warnl the oil, the bypass system
closes the line to the cooler. At the same time, the system opens a
line that bypasses the cooler. With the cooler line closed and the
bypass line open, the oil moves through the strainers and filters
directly into the engine. \\Then the oil becomes warm enough to
flow freely and to need cooling, the system closes the bypass line
anJ opens the cooler line. With the bypass line closed and the
cooler line open, the oil flows again through the cooler.
SCAVENGING
PUMP
STRAINER
HOUSING
DRAIN
VALVE
SCAVENGING
PUMP Fip;ure 44. Lube oil system
STRAINER FILTER AND ofa diesel engine showing
COOLER
DRAIN VALVE oil cooler bypass system
(striped lines)
DIESEL ENGINES
Engine Oil Supply Oil goes through a manifold (a pipe with several outlets) to five
Areas areas in an engine (fig. 45). These areas include
• the crankshaft, the camshaft, and the pushrod guides;
• the pistons, the piston pins, and the cylinder liner;
• the valve mechanism;
• the timing gear; and
• the fuel-injection system and governor.
If the engine has a turbocharger, the supply system moves oil
to it separately. Turbochargers run at very high speeds and there
fore need their own oil line. High-speed equipment must have
adequate lubrication or it quickly fails.
88
LUBRICATION SYSTEMS
Crank throws are machined and polished areas on the crankshaft to Crankshaft Lubrication
which the piston rods and piston-rod bearings are attached. Engine
crankshaft manufacturers drill holes from each main bearing to the
crank throws (fig. 46). Oil flows through these holes (passages) to the
piston-rod bearings. Oil also flows to the main bearings through a
hole in each bearing.
Part of the oil supplied to each main bearing forces its way
along the length of the bearing and then falls back into the crank
case. The other part of the oil goes through the passage in the
crankshaft to the adjacent rod bearing. Tills oil lubricates the piston
rod bearings, the piston wrist pins, and the piston. (Wrist pins are
hardened steel cylinders that attach the piston to the rod.)
DRILLED HOLE
THROW (passage)
DRILLED HOLE
(passage)
A drilled passage in the piston rod carries oil from the piston-rod Piston Lubrication
bearing to the wrist pin. Part ofthe oil lubricates the wrist pin, but
most of it spurts onto the bottom of the piston. This oil cools the
pistons.
An engine manufacturer may locate the camshaft above the valves Camshaft Lubrication
or in the cylinder block. In either case, the camshaft and the carns
on it operate the intake and exhaust valves. In most engines, the
cam does not directly touch the valve stern. Instead, the cam
contacts a pushrod, which, in turn, moves a rocker arm (see fig. 9).
The rocker arm actually operates the valve. Oil passages supply oil
to the camshaft bearings and the pushrod guides. (Apushrod guide
is a hollow metal Cylinder through which the pushrods move.)
DIESEL ENGINES
Rocker Arm and Valve Oil flows through a drilled passage in each rocker arm and lubticates
Lubrication the ends of the rocker arm and the top of the valve stem (fig. 47).
Also, a small amount of oil flows along the valve stem to lubricate
the valves.
ROCKER ARM
DRILLED
PASSAGE
TOP OF
VALVE STEM
«-1-- VALVE
Timing Gear Lubrication Diesel engines have a timing gear train (a set of gears that drives
various engine parts; fig. 48). The crankshaft drives these gears.
Engine parts driven by the timing gears include the oil pump, the
valve mechanisms, the fuel injectors, and the water pump. Also, in
many cases, the timing gears drive hydraulic pumps and other
accessories attached to the engine. Oil flows to the timing gears
through small lines and passageways, many of which are located in
the engine block (fig. 49).
Figure 48. Set oftiming gears in a heavy-duty diesel engine
DIESEL ENGINES
Injector Pump and Engine lubricating oil goes to the fuel injector pump and the
GovemorLubricaHon governor to reduce friction and keep the rubbing surfaces clean.
On engines with a hydraulic governor, the oil pressure provides
much of the force needed to operate the governor, reducing the
force needed on the governor's shaft. Oil pressure also operates
speed limiters and shutoffcontrols on some engines. Aspeed limiter
prevents the engine from running too fast before the oil pressure
gets high enough to get oil to all the parts. Asafety shutoff control
shuts down the engine when oil pressure gets too low.
Fresh air entering through the base of an engine can create a Explosion Covers
problem when oxygen mixes with the oil in the crankcase. If a hot
spot occurs in the engine, the heat can cause the oil and oxygen to
explode and damage the crankcase. To prevent such damage, some
engines have spring-operated explosion covers (doors) fitted to the
crankcase. If an explosion occurs in the crankcase, the doors open
to release the pressure from the explosion and then slam shut to
prevent more air from entering. If the engine operator sees one of
the doors fluttering, the operator should notify the mechanic and
safely shut down the engine as soon as is practical.
Modern lubricating oil for diesel engines is better than ever. Oil Quality
Improved chemistry keeps oils from oxidizing at high tempera
tures. Special additives improve the oil's film strength at high
bearing pressures. They also keep the oil from foaming, which
reduces its ability to lubricate properly. Some additives prevent the
oil from failing under conditions ofheat and pressure. Others keep
the oil thin for cold-weather starting. Modern lubricating oils for
diesel engines are high-detergent oils that clean while they lubri
cate. (A detergent is a cleaning material incorporated into the oil.)
The detergent loosens dirt, varnish, sludge, and residues,
which then enter the oil. A dispersant in the oil suspends these
particles, which makes the oil look dirty. When detergent oil
appears especially dirty, this shows that the oil is doing its job by
suspending the dirt to keep it from harming the engine.
The lubricating properties of an engine oil practically never
wear out. The products of combustion, however, do contaminate
the oil as the engine runs and the additives' ability to protect the
engine and preserve the oil base wear out. If an engine operator
fails to change the oil on a regular schedule, the oil loses its ability
to lubricate properly.
93
DIESEL ENGINES
Sulfur Content of Impurities in fuel can cause lube oil problems in an engine. One of
Fuels and Oil the worst of these is sulfur. When an engine burns fuel with sulfur
in it, an acid is produced which eventually works its way into the
Quality lubrication system. Many lube oils have additives that neutralize
the acid to keep it from corroding engine parts.
The sulfur content of diesel fuels varies. Thus, the amount of
acid produced from sulfur in the fuel also varies. Diesel engine
operators should, therefore, adjust the oil-change schedule accord
ing to the fuel's sulfur content. The higher the sulfur content, the
more often the operator should change the oil.
Using the Proper \Vhen selecting the oil for an engine, the engine's location, its type,
Oil and the temperature of its surroundings must be known. The
manufacturer's recommendations for the kind of oil to use should
be followed.
For example, for warm-weather operations, the manufacturer
usually recommends using a heavy-weight (high-viscosity) oil.
Conversely, in cold weather, a light-weight (low-viscosity) oil is
usually recommended. In cold weather, an engine runs cooler than
it does in hot weather. At cool temperatures, a light-weight, low
viscosity oil flows more easily than a high-viscosity oil. Thus, in
cold weather, a light-weight oil lubricates the engine better than a
heavy-weight oil.
While the viscosity of the oil is important, it is not the only
quality to consider. It is essential to use only oil designated for use
in diesel engines. Oil manufacturers identify lubricating oils with
codes such as API 40-DS-HD. This means that the refiner made
the oil to American Petroleum Institute (API) specifications and
certifies it to be 4o-weightviscosity, to be suitable for diesel service
(DS), and to contain high-detergent (HD) additives.
Brands ofoil should never be mixed. If it becomes necessary to
add oil to the engine to bring the level to normal, the same brand
of oil as has been used previously should be used to fill the
crankcase. Oil manufacturers use different additives and blend
their oils differently, and sometimes the additives are not compat
ible or the blends may not work correctly ifmixed. When switching
from one brand of oil to another, the operator should change the
filters as well as dispose ofall the used oil in an environmentally safe
manner.
94
LUBRICAnON SYSTEMS
In the old days, an engine mechanic could take asample ofoi I from Detergent Oils
an engine, put it on a finger, and decide whether it needed
changing. If the oil looked dark and dirty, it was time to change it.
Today, the high-detergent oils used in diesels get dark almost
immediately. The detergent cleans inside the engine and breaks
down carbon deposits. As it cleans, the oil carries the dark carbon
particles into the filter system. The filter removes particles large
enough to harm the moving parts. The small particles, though they
are too small to damage the engine bearings, remain in the oil and
make it dark. Since an operator can no longer tell by looking at the
oil whether it is dirty, it is best to keep accurate records and change
it at recommended intervals.
Even though an operator changes the oil at recommended inter- Oil Contamination
vals, fuel can contaminate the oil and cause it to fail long before a
scheduled change. An observant motorhand can easily spot fuel
contamination. If the oil level gets higher as the engine runs, and
no one has added oil to the engine, then another liquid is getting
into the oil. If the liquid is water, the oil has a milky color. If the
liquid is fuel oil, the oil pressure gradually drops and the oil looks
clear. A mechanic should find the place where fuel is entering the
oil system and repair it promptly.
Operators should take an oil sample from each engine, label it, and Oil Testing
send it to a laboratory for testing at least every six months. Among
other things, lab tests can show whether personnel are changing
the oil frequently enough. They can also show whether any
internal leaks exist in the engine. Such tests determine oil-change
intervals, parts wear, and oil contamination.
95
DIESEL ENGINES
To summarize-
Lubricating oil
• puts a film between moving parts; this film prevents metal
to-metal contact and reduces friction and wear.
• cools internal engine parts.
• forms a pressure seal between the combustion chamber and
the crankcase.
• removes gummy compounds from inside an engine.
high as 3,000° to 5,ooo°F (1,600° to z,800°C). Much ofthis heat goes Cooling System
to the cylinder heads and walls, the pistons, and the valves. Unless the
cooling system carries this heat away, it damages the engine. Acooling
system, therefore, prevents damage to vital engine parts. The cooling
system also keeps the parts cool enough to work at their best. That is,
a part running too hot may not fail, but it will not give maximum
perfonnance.
The engine transfers heat to a fluid called coolant. A common coolant Coolant
is a mixture of water, ethylene glycol (commonly called antifreeze),
and other additives. Antifreeze not only lowers the freezing point of
water, it also raises the boiling point. Thus, amechanic adds antifreeze
to the water in the cooling system to keep the water from boiling away
as well as to keep it from freezing.
Another additive an engine operator may put in the coolant is a
corrosion inhibitor. Called chromates, inhibitors delay the fonnation of
rust and cut back on corrosion in the cooling system.
As the engine runs, it circulates the coolant through passages
and openings around the cylinders. The engine also drives a coolant
pump (a water pump). The coolant picks up the heat from around
the cylinders. The water pump sends the hot coolant to a radiator
97
DIESEL ENGINES
SURGE TANK
HOTWATER ...............
FROM ENGINE ~'----I
,~ 1AIR IN
AIROUT~ • • • r
COOLED WATER ~
TO ENGINE ~ '-----L_-.J BonOMTANK
RADIATOR
Engine Fans The engine drives a fan that blows air over it and, at the same time,
draws air across the radiator's fins and rubes. The blown air
removes the heat from the fins, By the time the coolant gets to the
radiator's bottom tank, it is much cooler than when it entered the
top. The water pump circulates the cooled-off coolant back to the
engine to start the cycle over.
COOLING SYSTEMS
A heat exchanger is like a radiator except that mming air does not Heat Exchangers
carry away the heat in the coolant. Instead, a liquid from an outside
source that is cooler than the hot engine coolant carries the heat
away. A heat exchanger, like a radiator, has several tubes. Unlike
those of a radiator, heat exchanger tubes do not have tlns. The
engine circulates coolant through the tubes (fig. 5 I). The tubes are
surrounded by a moving raw water bath that is a lot cooler than the
hot coolant corning out of the engine. So, in a heat exchanger,
instead of air carrying the heat away, raw water removes the heat
from the engine coolant. (Raw water is water taken directly from
a source, such as the sea, and it is not treated.)
Aheat exchanger has some advantages over a radiator, especially
on large, stationary engines (like the ones on arig). For one thing, the
engine does not have to provide power to a fan. For another, the lack
of a fan reduces noise. For still another, heat exchangers take up less
space than radiators. Compactness is important offshore, where
personnel and equipment take up every bit of space. Finally, heat
exchangers work better than radiators because the temperature ofthe
water that serves as the cooling element in a heat exchanger is usually
a lot cooler than the temperature of the air that cools a radiator.
RAW
WATER
. . . OUT
HOTWATER ..............
WATER TUBES
COOLED+
WATER TO
ENGINE
+
. RAW
WATER
IN
HEAT EXCHANGER
99
DIESEL ENGINES
Coolant Flow
Whether a rig's engines use radiators or heat exchangers, the key
to cooling the engine is the flow of coolant through it (fig. 52).
When the engine runs, it drives a coolant pump (the water pump),
which moves coolant to the oil cooler. After cooling the oil, coolant
goes into the cylinder block, where it flows around the cylinder
liners and into the cylinder head. It then flows around the combus
tion chambers and into pockets (jackets) around the valves. After
removing heat from all these places, the coolant goes through pipes
(a manifold) and into the top tank ofthe radiator or heat exchanger.
The coolant then flows through the radiator or heat exchanger
where it is cooled and recirculated through the system.
TOP TANK
UNDER
PRESSURE
: ..
..
..J AIR FLOW
~ MAY BE IN
• z OR OUT
o~
o
~
COOLED
FLUID
BonOM
TANK
Pressurized Cooling
Many engines have pressurized cooling systems. A pressurized system
circulates the coolant under 5 to r5 psi (35 to I05 kPa) ofpressure,
which is higher than atmospheric pressure. Circulating coolant at
this higher pressure has advantages. For one thing, pressure raises
the boiling point of the coolant. Increased pressure, along with
antifreeze, keeps the coolant from boiling away at temperatures
above 2 r 2 OF (roo°C). Some modern engines circulate coolant at
temperatures higher than the boiling point of water; however,
most maintain a temperature of r8SoF (85°C).
100
COOLING SYSTEMS
Even though almost everyone calls it a radiator, a radiator is really More About
a liquid-to-air heat exchanger. Heat in the liquid coolant goes into Radiators
the air that is forced through the radiator by a fan. A good flow of
cool air through the radiator is absolutely essential to efficient heat
transfer. Likewise, a good flow of coolant is also necessary to carry
heat away from the engine.
When two fluids (like air and liquid coolant) are in contact at
different temperatures, the two temperatures tend to equalize.
That is, the hotter fluid warms the cooler fluid and the cooler fluid
cools the hotter fluid. So, to cool an engine with a radiator, the air
must be at a lower temperature than the coolant, with no less than
a roo to r SOF (SO to 8°C) temperature difference. An 85°F (47°C)
difference is better. The smaller the temperature difference, the
large'r (and thus more expensive) the system has to be to give
adequate cooling.
ror
DIESEL ENGINES
Radiator Size The engine manufacturer must provide a radiator that is able to
cool the engine under the most severe conditions. A f<ldiator that
is too small may cause the engine to overheat; moreover it restricts
the flow of coolant. As a result, the water pump, unable to keep a
positive pressure on the restriction created by the small radiator,
may develop negative pressure. \Nith negative pressure, the pump
draws air into the system. Air in the coolant reduces its cooling
ability, since air does not transfer heat as well as liquid does.
Coolant Flow The builder must also provide a radiator that allows the engine to
circulate an adequate amount of coolant through it. In fact, the
volume of flow through the radiator is just as important as the
number of tubes and fins and the depth (height) of the radiator.
Moreover, the manufacturer must install coolant manifolds that
do not restrict the flow of coolant to and from the radiator. Crew
members should therefore not make any modifications that may
restrict coolant flow. Also, when crew members or mechanics install
or reinstall coolant hoses or pipes, they should make sure that they do
not trap any air at the connections. Air pockets can block coolant flow
and let air into the system, which causes corrosion.
Fans Engine makers ensure that the radiator fan is the right size. They
design the fan to nm at the correct speed to move air efficiently
through the radiator. Fan design takes into careful consideration
the necessary number of blades and the best spot for optimal
operation. Crew members should therefore not make any modifi
cations to the engine fans without consulting the manufacturer.
102
COOLING SYSTEMS
A radiator is a simple device with no moving parts. It reduces the How Radiators
temperahlre of the coolant flowing through it. The coolant can Work
then efficiently cool the engine.
Hot coolant from the cylinder heads enters the top (surge) tank of Top Tank
the radiator (see figure 50). The top tank provides space for the
coolant to expand into as the engine heats it. It also serves as storage
space for coolant and directs it across the tubes (the core) of the
radiator. The radiator core is the heat exchanger. Along with the
fins, it transfers the heat carried by the coolant to the air.
1°3
DIESEL ENGINES
Fins The fins on the llJhes pass heat to the air that flows through the
radiator by prmiding IJrge surface areas for exposure to cooling
air. Radiator damage such as that shown in figure 53 reduces air
flow, while Jirt and trash between the fins keep them from
radiating heat (fig. 54).
---_. -
. '.
.........
~~._.
_._._. ....
-
-----
- r ".
--
Figure 53. Radiator damage Figure 54. Dirt and dust plug
reduces air flow. air passages in a radiator.
Tube Spacing How the tubes are spaced determines the capacity of the radiator.
The manufacturer must put enough tubes in the radiator to allow
the coolant to flow freely. Too many tubes, however, block air from
the tubes farthest from the front of the radiator. That is, tubes that
are behind others may not get very much air flow across them
because the front-most tubes block it. The radiator designer has to
balance .putting in enough tubes to allow free flow of coolant
against putting in so many that some do not radiate heat to the air.
1°4
COOLING SYSTEMS
Rig builders try to locate the engines in such away that cooling air Air Flow
passes through the radiator core only once. Ifhot air-air that has
already passed through the radiator-backflows through it, the hot
air cannot remove as much heat as cool air. Also, backflow inter
feres wi th the flow ofcool air, further reducing heat removal. Thus,
rig designers often install air tunnels (air ducts) that force flow over
the radiator and prevent backflow, ensuring that only cool air
reaches the radiator.
Wind can interfere with air flow through the radiator. Astrong
wind blowing against the direction of flow can create a dead space
around the radiator. For example, if the fan is moving air to the south
and the wind is also coming from the south, the fan blows against the
natural flow ofair. As aresult, astrongwind can reduce orstop air flow.
To prevent air stagnation, crew members can put up wood or metal
barriers to block the wind. Or, automatic shutters mounted in front
of the radiator can regulate air flow (fig. 55)' The shutter control
senses when wind direction is offsetting the direction ofair flow and
partially closes the shutters. The partially closed shutters block the
wind but allow air to flow through the radiator.
1°5
DIESEL ENGINES
Coolant Water The quality of the water used to make up the coolant should be
Quality high. Experts say that water too dirty to drink is too dirty to put in
a radiator. Foreign material in the water can reduce the ability of
the coolant to remove heat.
Dirt Dirt in the coolant can plug water passages in the engine and large
particles can completely block radiator tubes. Blocked tubes pre
vent coolant from circulating properly and the engine can over
heat. It is very important, therefore, to use coolant that does not
have dirt, clay, or trash in it.
Dissolved Minerals Dissolved minerals in the water can also be a problem. If the
coolant boils, dissolved minerals form very hard deposits that stick
tightly to internal surfaces. Calcium carbonate (lime) is a common
deposit, because it is found in a lot of water sources. Lime deposits
are very poor conductors ofheat; instead, they are good insulators.
As a result, a lime deposit of V32 in. (less than I mm) can insulate as
much as 2 in. (50 mm) of cast iron. Very little heat can radiate out
of the engine into the coolant passages if lime deposits exist.
H~andCOz Minerals are not the only problem with water quality. Hydrogen
sulfide (HzS) and carbon dioxide (CO z) often occur in water that
is in contact with decaying leaves and vegetation. If a rig gets its
coolant water from a creek or pond, operators must be aware ofthe
dangers posed by HzS and COz. Both substances corrode copper
surfaces, and manufacturers often make radiator tubes from copper
or copper alloys.
106
COOLING SYSTEMS
1. Only clean, soft water that is free from silt should be used. How to Protect the
Organic material or sulfur should not be allowed to Cooling System
contaminate it.
2. The engine's head gaskets must be properly tightened.
Head gaskets provide aseal not only between the cylinder
head and the crankcase, but also hetween the oil passages
and coolant passages in the head and crankcase. Loose
and leaky head gaskets can let coolant get into the oil and
contaminate it.
3. Water pump seals must be tight and free of leaks; other
wise, air can get into the cooling system.
4- All hose and pipe connections must be tight and free of
leaks.
5. The top tank in the radiator must always be full of
coolant. A full top tank keeps out air.
6. The water pump must be lubricated ~ccording to the
manufacturer's specifications for lubricant, procedure,
and schedule.
7. Oil coolers must be kept clean and free of sludge and
buildups.
8. The cooling system should be cleaned and flushed on a
periodic basis, following the instructions of the manufac
turer or the rig supervisor.
9. The coolant should be tested regularly according to the
specifications in the rig maintenance program. Anti
freeze and other additives should be renewed as often as
is necessary to keep them working well.
10 7
DIESEL ENGINES
Cooling System Engine operators should check the cooling system on aregular and
Checks routine basis. Some items to check indude-
I. the tension on the belt th:H drives the water pump. This
belt runs from an engine pulley to apump pulley. The belt
tension must be kept tight enough to turn the pump at the
proper speed. If it is too loose, the belt slips and does not
turn the pump properly. A belt with too much tension,
however, can wear out the pump bearings very quickly, so
it should not be overtightened.
2. the water-pump shaft packing, or seals (fig. 56). These
COVER GASKET
PACKING BUSHING PACKING
NUT NUT
PACKING
GLAND
PACKING
BODY-______
r08
COOLING SYSTEMS
Rig builders often put the engines in a room or in some kind of Engine Rooms and
enclosure. It is important for them to provide adequate ventilation Ventilation
in an enclosed space. If they do not, an engine can overheat, even
if its internal cooling system is working well.
As an example, assume that crew members installed three 350
hp (245-kW) engines in a rig compound. In one minute of running
time, the engines burn] 59,000 heat units. Of these] 59,000 units,
the work the engines do accounts for only 44,500 units (about
28%). Subtracting 44,500 from] 59,000 leaves I ]4,500 heat units
to account for. The exhaust stack disposes of 47,500 heat units.
The engines throw the remaining 67,000 heat units into the air
around them. The production of 67,000 heat units per minute
could increase the air temperature in the engine room by 420°F
(216°C) every minute.
In short, it can get very hot around the engines unless the rig
builder provides proper ventilation. A good ventilation system
r~places the engine room air as fast as it heats up. In the example,
the yentilation system would have to move 186,000 ft3 (5,265 m3)
of air every minute, assuming a 20°F (IIOe) rise of 60°F (16°C)
outside air. The fans on the engine radiators can move this much
air if the engine room has enough openings to outside air. If the
engines overheat, yet their cooling systems are in good working
order, then it may be that there are not enough openings in the
room or enclosure. What is more likely, however, is that a crew
member may have blocked one or more of the openings. Rig
personnel must ensure that all openings are clean and unblocked
by any debris or equipment.
1°9
DIESEL ENGINES
More About Heat A heat-exchanger cooling system uses a bundle of tubes inside a
Exchangers closed shell (fig. 57)' Note that a heat exchanger is small compared
to a radiator, even though the whole exchanger system takes up as
much space as a radiator, or even more.
A heat exchanger consists uf two separate water systems. One
is the raw water system. Raw water, instead of air, removes heat
from the engine coolant. The second water system is the engine
coolant system. This system is exactly like the coolant system in an
engine with a radiator.
Raw water, usually sea water if the system is offshore, enters the
heat-exchanger shell and circulates around hollow tubes. A sepa
rate pumping system moves raw water through the exchanger's
shell. Engine coolant circulates through the tubes. Since the raw
water is cooler than the engine coolant, the raw water removes
heat. Note that coolant and raw water never corne into direct
contact. Coolant stays inside the tubes while raw water circulates
in the shell outside the tubes.
TEMPERATURE GAUGE
(water from engine)
ENGINE
TEMPERATURE
SWITCH (ETS) IMMERSION
HEATER
TEMPERATURE
SWITCH (IHTS)
TEMPERATURE
REGULATING
VALVE
IIO
COOLING SYSTEMS
Raw water exits the shell after removing heat from the coolant
in the tubes. A special pump may recirculate the raw water.
Offshore, however, where there is an abundant amount ofcool sea
water available, the system usually does not recirculate it.
Hot coolant from the engine goes through a discharge mani
fold. Many systems have a temperature gauge at the exchanger.
The operator can read the coolant temperature leaving the engine
from this gauge. An engine temperature switch (ETS) senses over
heating and shuts down the engine if overheating occurs.
Coolant then goes through piping and passes a temperature
regulating valve (a thermostat). When the valve is cold, it closes to
divert coolant through a bypass line to the oil cooler.
In extremely cold climates, such as in Alaska, Siberia, and the
like, an immersion heater temperature switch (IHTS) senses very cold
coolant and turns on an immersion heater. The heater helps heat
the water as the engine warms up.
After leaving the oil cooler, coolant goes through two lines to
two water pumps. Each pump feeds coolant to the one side of the
engine. A temperature gauge in the inlet allows the operator to
check coolant temperature as it enters the engine.
A water-expansion tank completes the installation. As the
coolantheats up and expands, it vents into this tank. An overflow
pipe on the expansion tank prevents the expansion tank from
overfilling.
Note that the rig builders always place the heat exchanger
lower than the highest point ofthe engine because this keeps air out
of the system.
III
DIESEL ENGINES
To summarize-
The cooling system
• removes about one-third of the heat produced by an engine.
• carries heat away from cylinder heads, pistons, and valves.
• prevents damage by keeping engine parts cool.
Radiators
• transfer coolant heat to the airvia tubes, fins, and engine fan.
Heat exchangen
• transfer coolant heat to water via tubes surrounded by the
water.
Coolant
• must be kept clean.
• must not have too many dissolved minerals in it.
• should not have any H 2S and/or CO 2 in it.
• must be free of oxygen.
Cooling system checkpoints
... water pump drive-belt tension
• water pump seals
• hoses, connections, radiator cap
• thermostat
112
Air-Intake Systems
T
T
T
113
DIESEL ENGINES
Air Cleaners In both naturally aspirated and supercharged engines, air cleaners
remove much of the dust and dirt that is in the air. All of the air that
goes into the engine should pass through the cleaners first.
Types of Air Cleaners Manufacturers make two types ofair cleaner: dry and oil bath. Ad1)
,
air cleaner uses centrifugal force and filter elements to remove dust
and dirt from the intake air. An oil-bath cleaner uses oil with filter
elements to remove particles from the air.
A cleaner not only has to filter the air, but it also has to let in
the correct volume of air. Because dirty air cleaners reduce the
volume of air, it is important to clean or replace air cleaner
elements when they become dirty. Note that air cleaners do not
filter out every particle ofdust. If they did, the operator would have
to service them (change or clean the filter) so often as to be
impracticable.
No definite rule exists on how often to clean or replace the
filtering element of an air cleaner. A cleaner operating under very
dusty conditions needs more frequent service than one operating
in relatively clean air. Some air cleaners have an indicator that gives
avisual sign or warning when the cleaner needs servicing; however,
perhaps the best way to set up agood servicing schedule is to inspect
the cleaners frequently during normal operation and then set up a
schedUle that is reasonable for that operation.
Dry Air Cleaners Dry air cleaners, unlike oil-bath air cleaners, do not use liquids to
trap dirt and dust. Paper elements that fit inside a housing, along
with the centrifugal action of the air going through the elements,
act to clean the air. Paper elements that fit inside a housing, along
with the centrifugal action of the air going through the elements,
serve to clean the air.
114
AIR-INTAKE. SYSTE.MS
Operation
Heavy-duty dry air cleaners filter the air very well under all
operating conditions (fig. 58). Air enters the cleaner through a
perforated steel housing, then passes through a disposable safety
element that removes the biggest dust particles.
Inside the housing are steel tubes with vanes. After passing
through the safety element (a filter), the air crosses the vanes, which
cause the air to swirl. This swirling motion creates centrifugal force,
throwing the dust particles against the walls of the tubes. Pan of the
intake air then carries this dust into chambers. Once in the chambers,
special "vacuator" valves automatically open to dump the dust accu
mulated in the chambers. On models without valves, the dust collects
in the chambers, and the operator removes it by hand.
The remainder of the intake air reverses direction in the tubes
and spirals back along them. As centrifugal force continues to
remove dust particles, the tubes make the air reverse direction
again and enter a paper filter element. This paper element filters
the air once more before it enters the engine. With care, the
operator can clean the paper element several times before replac- .
ing it. Ahinged door on the side of the housing gives access to the
paper element, the safety element above it, and a retainer.
Rubber gaskets seal the elements and the housing. The hous
ing also has mounting flanges and outlets for the filtered air. At the
bottom of the housing is an inspection cover that can be removed
to allow the operator to manually remove dust from the chambers.
~~ ... ELEMENT
< ~V
AIR INLET
!~~
115
DIESEL ENGINES
116
AIR-INTAKE SYSTEMS
After the paper filter element has been replaced and the tubes
have been cleaned, the degree of air-intake restriction can be
measured by checking the pressure of the intake air before it goes
through the safety element and comparing it to the pressure after
it leaves the cleaner. If the pressure drop across the cleaner is
acceptable according to the manufacturer's specifications, then the
safety element does not need replacing. If, however, the pressure
drop is greater than specified, it is time to replace the safety
element. (It is important to remember that this procedure assumes
a new or a clean paper filter element. The manufacturer's service
manual will give detailed procedures and the equipment required
to measure pressure drop in other circumstances.)
Two types of oil-bath cleaner are available: a heavy- and a light- OiJ-Bdth Air Cleaners
duty model. They both work the same way; this text will focus on
the heavy-duty model.
Parts
The housing of a heavy-duty oil-bath air cleaner is a hollow metal
cylinder (fig. 59)' A rdatively small amount of engine oil (the oil
bath) lies in the bottom (the sump) of the housing, contained in an
inner cup and an outer cup. Two clamps hold the oil cups on the
bottom of the housing. A removable screen rests on top of the oil
cups, and above that is a fixed, metal-and-wool filter element.
AIR IN
AIR OUT
HOUSING
IOX~-- FILTER
ELEMENT
SCREEN
117
DIESEL ENGINES
Operation
Air enters through an opening in the top and flows down a center
tube to the oil bath. The air then goes up through the removable
screen assembly. When the air flow changes direction, larger
particles of foreign matter slow down and the oil and the screen
assembly remove them from the air. The particles then settle in the
oil cups at the bottom of the housing.
The air continues upward through the fixed element, which
removes the finer particles and the entrained oil. The air goes out
a side outlet near the top of the cleaner and flows through the
engine's air-inlet housing to the intake side of the blower.
SeNicing
I. The oil cups are removed from the cleaner housing after
the clamps that secure them have been loosened. The
screen is removed from the cups, and the dirty oil, is
emptied and properly disposed of. The inner cup and the ,
outer cup are then separated, and both are cleaned with
fuel oil. The fuel oil must be properly handled so that it
does not harm the environment or personnel.
2. The removable screen may be washed in solvent and dried
with compressed air. Its cleanness may be checked by
shining a light through it. An even pattern of light should
shine through; any blockages are unremoved dirt. If sol
vent and air cannot clean the screen, it should be discarded
and replaced with a new one.
3. The central tube may be cleaned by running a swab soaked
in solvent through it.
4. The oil cups are put back together and filled with clean
engine oil to the level indicated by a scribed line on the
inner cup. The oil used should be of the same grade and
viscosity as that in the engine. The oil cups must not be
overfilled, since the intake air could pull excess oil through
the air cleaner and into the engine. The oil has dirt in it,
which could harm the engine. Also, the engine could burn
the excess oil and overspeed. On the other hand, too little
oil reduces the efficiency of the air cleaner. Once the oil
level is correct, the removable screen is placed back on top
of the oil cups and the assembled unit is replaced in the
housing, securing it with the clamps.
118
AIR-INTAKE SYSTEMS
air cleaner.
Talcing offthe oil cups from the bottom of the cleaner, the
a new one.
Air cleaners stop working if not installed correctly or if not Additional Cleaner
maintained properly. Problems include leaks in the intake or outlet Maintenance
ducts, loose hose connections, and damaged gaskets. Such prob
lems can let dust-laden air completely bypass the cleaner and
directly enter the engine.
To ensure that the cleaner is doing its job, the operator
must-
I. keep the cleaner tight on the engine's air intake.
2. properly assemble the cleaner so that all its parts are oil
and air-tight.
5. remove the air inlet housing after servicing the air cleaner,
screen and the air inlet housing. All intake air passages and
119
DIESEL ENGINES
GEARS
HELICAL
ROTORS
~HOUSING
120
AIR-INTAKE SYSTEMS
@/@J~
LOCK COUPLING ROLLER SEAL
I
WASHER HUB BEARING SLEEVE
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GEAR
NUT
To compress the air, the blower has two spiraled (helical) rotors, each
with blades Oobes) that rotate inside ahousing. The engine drives the
rotors with gears at about twice the engine's speed, causing them to
rotate in opposite directions at the same speed. As they rotate, the
lobes compress air drawn through an air cleaner on top ofthe housing.
The compressed air exits the blower from the bottom or the side of
the housing and goes into the engine's air-intake manifold.
Each rotor has a shaft at both ends that turns on ball and roller
bearings. Seal rings and retainers fit the rotor shafts into an end
plate on the front and back of the housing. Intenneshing gears on
the end of each rotor transfer engine power to the rotors.
The rotors' helical shape provides continuous and unifonn
displacement ofair. The space (clearance) between the rotor lobes
and the housing is close-o.007 in. (0.18 mm) on the leading edge
of the lobe and 0.013 in. (0.33 mm) on the trailing edge ofthe lobe.
Close clearances ensure that the blower develops a maximum
amount of pressure.
121
DIESEL ENGINES
Causes of Blower Failure A blower may fail for one or more of the following reasons:
I. The intermeshing gears wear and cause improper clearance
between the two interlocking rotor lobes. Increased clear
ance reduces the pressure of the air the rotors supply to the
engme.
2. The blower draws in dirt, which scores the rotors and the
housing.
3. Loose shafts or worn bearings cause contact between the
rotors and the end plates.
4. Worn oil seals let lubricating oil into the housing. Lubricat
ing oil reduces the efficiency of the lobes; instead ofpushing
against air alone, they have to push against oil as well.
Turbochargers
A turbocharger is made up of a centrifugal compressor and a
turbine that work together to compress air for the engine to use in
combustion (fig. 62). It is similar to a blower in that it forces
precompressed atmospheric air into the engine to increase power.
The main difference is that a turbocharger is driven by the engine's
exhaust. A centrifugal compressor has a rotating device (a rotor)
with several blades on it. As the rotor turns, the blades draw air into
a housing that surrounds the rotor and compresses the air.
Located close to the compressor, and sharing the same drive shaft,
is a turbine. The turbine, like the compressor, has several blades inside
a housing. Exhaust gases leaving the engine strike the blades of the
turbine to tum it. Since the compressor and the turbine have the same
drive shaft, the turbine's movement turns the compressor. As the
compressor blades turn, they draw in outside air and compress it. The
compressor then forces the compressed air into the engine's air-intake
manifold. The pressure of the air entering the manifold depends on
the engine's load and the turbocharger's speed.
Modern turbochargers run at 60,000 to 90,000 rpm. This very
high speed requires a constant flow oflubricating oil from the oil
pump. Moreover, the compressor's housing may get as hot as
3so°F (I7S0C). The turbine housing, because hot exhaust gases
drive it, can getas hot as I ,200°F (6so°C). Therefore, the compres
sor and turbine need alot ofoil to cool them. Oil also lubricates the
drive shaft and bearings.
Manufacturers also have to consider that turbochargers, be
cause they run at such high speed, take time to slow down after the
operator reduces the engine's throttle setting. The engine slows
immediately, as does the oil pump's speed and output pressure.
122
AIR-INTAKE SYSTEMS
AIR DISCHARGER
TURBINE WHEEL
AMBIENT
AIR INLET
COMPRESSOR
WHEEL
EXHAUST
GAS INLET
~ EXHAUST
.......... AMBIENT
12 3
DIESEL ENGINES
Aftercoolers Compressed air leaving the turbocharger is hot. Hot air is undesir
able for two reasons: first, it can overheat the engine, and second,
hot air is not as dense as cool air; that is, hot air does not contain as
much oxygen as cool air. As a result, cool air with more oxygen in
it mixes better with the fuel and ensures that all the fuel burns.
To reduce high temperatures, engine builders install an
aftercooler on turbocharged engines. Coolant from the radiator
cools one type of aftercooler; another type is cooled by air. On
aftercoolers using radiator coolant, the coolant circulates around
the hot air leaving the turbocharger, bringing the temperahIre of
the air very close to that of the coolant. On aftercoolers using air,
the engine fan draws air through the radiator and cools the
turbocharger's discharged air.
Back-Pressure and
Turbochargers increase the back-pressure on the engine's exhaust
Temperature Effects
system. They also increase the temperature of the intake air. Back
pressure is pressure acting against the free flow ofexhaust gases from
the engine. Too much back-pressure reduces the engine's power;
the pistons and cylinders have to work harder to push exhaust gases
out of the engine. Turbochargers increase back-pressure; because
exhaust gases are needed to drive the turbine, their free movement
into the atmosphere is restricted.
Also, the higher the intake-air temperature rises, the less dense
it becomes-that is, the less oxygen it has in it. When the intake air
has less oxygen, the engine generates less power from combustion.
Turbochargers raise the temperature ofintake air because the hot
exhaust gases driving the turbine also heat up the turbocharger's
nearby compressor. The power gained by supercharging an en
gine, however, significantly offsets the losses from back-pressure
and high temperatures.
AIR-INTAKE SYSTEMS
To summarize
To clean intake ail'
• Two types of air cleaners are used: dry and oil-bath.
Dry air cleanen have
• a perforated steel housing.
• steel tubes with vanes that create centrifugal force to cause
dust to fall into chambers.
• "vacuator" valves to remove dust automatically from cham
bers (some must be manually cleaned).
• a paper filter element, which can be carefully cleaned with
compressed air, water, or solvent.
• a safety element, which must be replaced if clogged.
• gaskets, which must make a tight seal; if they fail, they are
replaced.
Dry air cleaners should be serviced on a regular basis.
Oil-bath air cleaners use
• an oil bath to which dust adheres.
• a removable screen, which must be cleaned on a regular basis.
• afixed element, which can sometimes be cleaned but must be
replaced if it cannot be adequately cleaned.
Forced-air induction increases the pressure (and density) oftbe intake air.
Two types offirced-air induction are
• superchargers (blowers)-Roots blowers use two helical
rotors driven by the engine to compress the intake air.
• turbochargers-turbochargers have an engine exhaust
driven turbine that drives a centrifugal compressor at very
high speeds; the compressor increases the pressure and
density ofthe intake air. Turbocharged engines may also use
an aftercooler. Turbochargers can be used with either a
two-stroke or a four-stroke engine.
Aftercoolers use engine coolant or air to reduce the tempera
ture of the compressed air entering the engine
12 5
Exhaust System
Besides conducting exhaust gases from the engine, the exhaust Purposes
12 7
DIESEL ENGINES
Exhaust System Except on mrbocharged engines, which may not hayc mufflers, a
basic exhaust system (fig. 63) consists of:
Parts
• an exhaust manifold
• an exhaust pipe
• a muffler (exhaust silencer)
• a tail pipe
EXHAUST PIPE
EXHAUST MANIFOLD
Exhaust Manifold An exhaust manifold connects the exhaust port of each cylinder to a
single exhaust pipe. On engines with two banks of cylinders, some
manufacmrers may install one exhaust manifold to carry the
exhaust from both banks, while others may install two manifolds
one on each bank.
On large engines, manufachlrers weld all parts of the manifold
together and put a waterjacket around the whole thing. The cooling
system circulates coolant through the jacket, reducing the tem
perahlre of the manifold. Water-cooled exhaust manifolds lessen
the danger of burning those who work around the engine. They
also reduce the chance of a fire inside an engine ·room. What is
more, cool exhaust gases in the exhaust manifold reduce back
pressure on the engine. We know that hot air expands, whereas
cool air contracts. Expanding hot air puts back-pressure on the
engine exhaust, reducing the engine's power. Contracting cool air
reduces back-pressure and does not decrease engine power.
The temperahlre ofan uncooled exhaust manifold varies as the
engine load varies. The higher the engine load, the hotter the
manifold becomes; conversely, the lighter the load, the cooler it
128
E.XHAUST SYSTEM
The exhaust pipe connects the exhaust manifold's outlet to the Exhaust Pipe
muffler. The pipe should be short and have as few turns as possible.
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o 100 200 300 400 500 600 700 800 900 1000 1100 1200
MAXIMUM HORSEPOWER
12 9
DIESEL ENGINES
A tail pipe comes out of the muffler or the exhaust pipe and carries Tail Pipe
the exhaust gases to the atmosphere. The length of the tail pipe
depends on how far it has to conduct the gases from the engine
room or the engine enclosure.
It is important to remember, however, that engine builders
make the tail pipe a certain length to accommodate the way a
particular engine expels exhaust gases. Exhaust gases leave the
muffler or the exhaust pipe in pulsating waves. When each wave
reaches the tail pipe outlet, the atmosphere at the outlet reflects
some of wave back down the pipe. The reflected wave should get
back to the muffler or the exhaust pipe at the right time. That is,
the reflected wave should arrive, not at the moment ofa fresh wave,
but between two waves. The reflected wave's reaching the muffler
or exhaust pipe between new waves prevents back-pressure. En
gine installers therefore cut tail pipes to a specific length to make
the reflected waves arrive at the muffler or the exhaust pipe at the
right time to prevent back-pressure from pulsations. Operators
and mechanics should not change a tail pipe's length without first
consulting with the manufacturer.
Engine installers cut the end of the tail pipe at an angle other
than 90°-say at 45° or so. In other words, they cut it on a bias.
Cutting the end of the pipe on a bias reduces noise. If the gases left
the pipe in a straight path, as they would from a straight-cut pipe,
they would come out with a fast, noisy puff. But when the gases
leave on the angled path created by the bias, they gradually spread
out and thus make less noise.
When a tail pipe is erected vertically, it is called a stack (fig. 65).
Where a stack goes through a roof or ceiling, the builders install a
flexible collar between the pipe and the opening in the roof. The
collar allows the pipe to expand and contract with changes in
temperature.
To summarize-
The exhaust system
• conducts exhaust gases from an engine's cylinders to the
atmosphere.
• muffles the noise that escaping exhaust gases make.
• carries exhaust gases and smoke away from the engine.
• may power hlrbochargers.
Exhaust system components
• exhaust manifold
• exhaust pipe
• muffler (exhaust silencer); not always used on turbocharged
engmes
• tail pipe
Exhaust manifolds
• often have a water jacket for cooling.
• expand and contract with temperature changes.
Exhaust pipes
• connect manifold's outlet to muffler.
13 2
Starting Systems
...
...
...
E ngine builders install various devices to start diesel engines.
Usually, the builder mounts the starter on or near the engine.
The starter rotates the crankshaft so that the pistons can compress
the air in the cylinders. When the air reaches the proper pressure
and temperature, it ignites the injected fuel and the engine begins
running on its own.
Electric motors, air motors, hydraulic motors, and gasoline en Types of Starters
gines are all mechanisms used to start an engine. An"other means is
to inject compressed air into the cylinders. Very small diesel
engines can be started by turning a hand crank.
A diesel engine has to reach a certain speed to build up enough Why Diesel Engines
pressure and temperature for ignition. The speed depends on the type May Not Start
and size of the engine, its condition, and the temperature of the
surrounding air. In some engines, the starting speed may be as low as
70 rpm, but a small engine may have to be turned up to 3,000 rpm.
To ensure a quick start, the starting device must turn the crankshaft Low-Pressure Problems
fast enough to compress the air to the proper temperature. If the
starter turns the engine over too slowly, the air in the cylinders
cannot compress and get hot enough to ignite the fuel. Air leaks
constantly through the small spaces between the piston rings and
the cylinder wall, but if the crankshaft turns fast enough, its speed
overcomes the leaks and adequate compression occurs.
Heat loss to the cold metal walls of the cylinder may lower the air Low-Temperature
temperature so much that ignition temperature is hard to reach. Problems
Further, badly worn cylinder walls and piston rings allow too much
air to leak past them. No matter how fast the crankshaft turns, the
air cannot compress enough to reach ignition temperature.
133
DIESEL ENGINES
Diesel engines start and run at their best if the average tempera
ture is about 70°F (20°C). An engine that has been shut down for
several hours when the temperature is\vcll below 70°F (zo°C)maynot
start promptly. The starter may not be able to turn the engine fast
enough to get the necessary pressure and temperature for compres
sion. Or, even if the starter turns the engine over rapidly, the
compression temperature may still be too low for ignition.
Lubricating oil gets thicker (its viscosity increases) as the
temperature drops. Increased viscosi ty makes it hard for the starter
to turn the engine over quickly. In some installations, a special
heater raises the temperature of the engine coolant, which in turn
raises the temperature of the oil. Manufacturers equip some small
diesel engines with an electric heater in each cylinder's water jacket
to warm the oil. In any case, raising the oil temperature reduces its
viscosity, thus making engine start-up easier.
To see how low temperatures affect start-up, let us suppose that
the intake-air temperature is 70°F (zo°C) and that an engine has a
compression ratio of 14 to 1 (the piston compresses the air to a
pressure 14 times higher than its beginning intake pressure). In this
case, the final compression temperature is 700°F (3 70°C), which is hot
enough to ignite the fuel. But ifthe intake-air temperature ofthe same
engine were to drop to 40°F (SoC), the final compression temperature
would be only zoo°F (90°C). This temperature is much too low for.
ignition to occur with normal fuel. Note that most diesel engines have
compression ratios much higher than 14 to I; but, even so, ifthe intake
air's temperature is low, tlle engine cannot start.
Rig owners install most large engines in rooms where the
temperature rarely falls below 70°F (20°C). In situations ofgreater
exposure to the elements, however, the following techniques may
be used to raise the temperature of the intake air:
1. using electric intake-air heaters;
z. heating the jacket coolant; or
3. installing glow plugs in the cylinders.
Electric Starters Rig owners sometimes install electric starters on relatively small
diesels, such as those used to generate electricity on the rig.
Usually, power to turn the starter comes from a storage battery,
similar to the one in an automobile. The manufacturer sizes the
battery to match the engine's cold-weather starting requirements.
Cold reduces the battery's output; yet, a cold engine needs a lot of
torque to start. Thus, a battery big enough to start the engine in
warm weather could fail in cold weather.
134
STARTING SYSTEMS
Electric starters use direct Cll1nnt (DC) rather than alternating Direct Current Versus
current (AC). In a DC system, electricjty flows in one directjon Alternating Current
fi'om the battery through wires (cables) to the starter. In an AC
system, like the electrical system in your home, electricity flows
rapidly back and forth (alternates) between the source and the item
being powered. Direct current is better for engine start-up systems
because a battery can store direct current for a relatively long time,
and the starter can draw on it when needed.
An electric start-up system consists of a storage battery, cables Starter System Parts
from the battery to a DC motor, and a DC motor. It also has a
mechanical connection (usually gears) between the DC motor and
the engine crankshaft. The system also has an engine-driven
generator to charge the battery. Figure 66 shows an electric starter
on a diesel that drives an auxiliary power unit on a rig.
Electric starter motors are heavy-duty devices. They can,
however, overheat jf anyone operates them for too long a period.
135
DIESEL ENGINES
How Electric Starters Two gears connect the starter motor to the engine crankshaft. One
Work is a pinion gear on the end of the shaft of the starter motor (fig. 67)'
The other is a ring gear, which is on the outer circumference of the
engine's flywheel (not shown in the figure). (The flywheel is
connected to the crankshaft.) When the operator activates the
starter, battery current moves a friction clutch (often called a
Bendix; see fig. 67) forward.
TERMINAL
POLE SHOE
COVER
(LAMINATED)
BAND
DRIVE
BENDIX DRIVE HOUSING
(FRICTION-
COMMUTATOR CLUTCH TYPE)
COMMUTATOR
END FRAME ARMATURE
Figure 67. Cross section ofa Bendix-type starting motor for small
engznes
LINKAGE
OILER
SHIFT
LEVER
BRONZE
BEARING
When the engine runs, it turns a constant-voltage generator that Generators and Cutouts
recharges the battery. A constant-voltage generator is a generator
that puts out the same voltage regardless ofthe engine's speed, with
two limitations. If the engine stops or runs very slowly, the
generator cannot charge the battery. To keep the battery from
discharging while the engine is idling or stopped, the manufacturer
installs an automatic cutout in the system. The cutout electroni
cally disconnects the battery from the generator so that the
generator cannot discharge the battery when the engine is running
slowly or not at all.
137
DIESEL ENGINES
Batteries A batte}) provides direct current for the starting motor. Most
batteries are of the lead-acid type. Lead-acid batteries have several
plates, thin metal strips oflead and lead oxide. The plates reside in
compartments (cells) within the battery case. Water containing an
electrolyte surrounds the plates. (An eiect1'olyte is a substance that
conducts electricity. In this case, the electrolyte is an acid dissolved
in water.) Lead and lead oxide produce electricity when water with
acid in it surrounds them. The electricity (DC) flows from the
battery's negative terminal (or post) to its positive terminal. Heavy
duty electric wire (cable), connected to the positive post, conducts
the direct current to the starter motor. The negative post has a
heavy-duty grounding strap to complete the DC circuit and allow
current to flow from the battery to the starter motor.
Another characteristic of lead-acid batteries is that they can be
recharged. An engine generator can charge them constantly as the
engine nms. Or, if the battery loses its charge, an operator can
attach a battery charger to the battery terminals and recharge it.
Care of Batteries
Air-motor starters work much like electric starters. Compressed Air-Motor Starters
air, instead of electricity, operates the starter. Like an electric
starter, an air starter has a pinion that engages the teeth on the
flywheel (fig. 69). Inside the starter housing, the manufacturer
mounts a cylinder equipped with vanes on a rotating shaft. To start
the engine, the operator opens avalve to let compressed air into the
starter housing, where it strikes the vanes. Because the vanesare at
a right angle to the centerline of the shaft, the air strikes them at
full force and forcefully turns the cylinder and attached shaft. The
turning force of the shaft actuates a starting motor. As it begins to
rotate, the starting motor causes the starting clutch to move the
pinion so that its teeth mesh with the teeth on the engine flywheel.
The turning pinion thus turns the flywheel and the crankshaft.
When the operator shuts off air to the starting motor, the pinion
teeth disengage from the flywheel teeth. If the starter fails to
disengage properly, it can seriously damage the engine.
AIR IN
HOUSING
ROTATING VANE
SHAFT AIR OUT
139
DIESEL ENGINES
Air Requirements Clean, water-free, and lightly oiled air operates the starter. The
pressure for the inlet air should be from TOO psi (7°° kPa) to IS0
psi (J ,000 kPa). An air reservoirthat is at least 23 ft3 (0.7 m3) in size
is required for a 1,000 hp (750 kVV) engine. To remove moisture
from the air, a water trap is placed in the air supply line. An oiler
installed next to the starter puts oj] into the air. Lightweight oil
should be used in the oiler so that itcan break the oil into a fine mist.
Cleaning an Air Starter After an air starter has been in service for some time, it can gum up
and not work properly. Fine dirt particles in the air and oil mixture
build up on the parts of the starter and cause it to malfunction or
fail. If the gumming problem is not too serious, the operator may
be able to clean the starter without disassembling it. Clean diesel
fuel mixed into the air supply may be run through the starter; this
procedure sometimes cleans the starter by dissolving the gum.
Hydraulic Starters A hydraulic startel can be used with a diesel engine. The GM
r
RESERVOIR
The starter system recycles the used fluid, which leaves the st(lrter
and goes into a rescD'oir. An engine-driven pump continuously
charges the (lccumulator during engine operation. If the operator
shuts down the engine for a long period, the accumulator loses its
charge. The manuf(lcturer therefore provides a hand pump that the
operator c(ln use to raise the (lccumulator pressure to the 1,500 to
2,500 psi (10,35° to 17,25° kP(I) required to start the engine.
Operators often inst,dl hydraubc starters on engines that
generate emergency electricity. t Iydraulic starters take very little
maintenance and are safer than electric systems. The only real
disadvantage of a hydraulic starter is its high initial cost, which is
several times higher than that of an air starter.
In some installations, the engine operator uses a gasoline engine to Gasoline Engine
operate a starter motor. The ga.lOline engine starter motor engages the Starters
flywheel of the diesel engine. A friction clutch, in combination with
V-belts or gears, connects the starter motor to the diesel engine.
The operator starts the gasoline engine by hand cranking it.
When ir:is running, the operator then engages the friction clutch by
moving a hand lever. The clutch makes the starter motor's pinion
engage the diesel engine's flywheel. When the diesel gets Underway,
the speed ofthe flywheel releases the pinion gear on the starter motor.
Operators sometimes use gasoline engine starting systems in
very cold climates. They first start the gasoline engine and allow it
to run until it is warm. They then route the gasoline engine's warm
coolant to the diesel engine. The warm coolant preheats the diesel
and makes it easier to start.
DIESEL ENGINES
Compressed-Air Large stationary and marine diesel engines often use compressed
Starting air stm1ers, in which compressed air is injected directly into the
engine's cylinders. A special valve directs compressed air to each
cylinder during the power stroke and during the exhaust stroke.
The compressed air causes the pistons to move rapidly until
enough pressure builds up to ignite the fuel.
The amount of compressed air needed to start a small engine
is about twenty-five times its total piston displacement. For a large
engine, the amount may only be about ten times its piston
displacement. An air compressor pressures up the air anywhere
from 125 to 250 psi (850 to 1,750 kPa).
Once a diesel engine has been started, it usually runs for long
periods. Because of this, the air compressor is usually fairly small
and does not need much power. While the engine runs, the
compressor has plenty oftime to restore the volume ofair required
for the next start-up. In some cases, the engine drives the compres
sor. In others, a gasoline engine or an electric motor drives the
compressor. Marine engines often drive compressors, because
equipment on the boat uses compressed air for other purposes.
Cylinder-injected compressed air can start a four-stroke en
gine with five or more cylinders, no matter what position the
crankshaft stopped at when the operator last shut down the
engine. On a four-stroke engine with four or fewer cylinders,
however, the operator must bar the engine. That is, the operator
must insert a steel bar into a hole on the rim of the engine's
flywheel and, using the bar as a lever, manually turn the flywheel
to rotate the crankshaft and pistons. The operator must bar the
engine until one of the pistons is on the down stroke, slightly past
bottom dead center and ready to take starting air.
Compressed air can also start a two-stroke engine with three
or more cylinders regardless of the position of the pistons inside
the cylinders. If the engine has only one or two cylinders, however,
the operator must bar the engine until one of the pistons is on the
down stroke.
STARTING SYSTEMS
143
DIESEL ENGINES
To summarize-
The starting system
• rotates the engine's crankshaft so that the pistons can build
up enough pressure and temperature to ignite the fuel.
• uses electric motors, <lir motors, hydraulic motors, gasoline
engines, or compressed air.
Electric starters
• use batteries as a source of power
• consist of battery, cables, DC motor, and mechanical con
nection (gears) between DC motor and engine crankshaft.
• have a pinion gear that meshes with ring gear on flywheel.
• use a battery that is recharged by means ofa generator on the
engme.
Air-motor starters
. • use compressed air to actuate starter.
• have a pinion that engages a ring gear on the flywheel.
·needc1ean, lightlyoiledairat IOOto 125 psi (700 to I ,000 kPa).
Hydraulic starters
• use hydraulic fluid stored under nitrogen pressure.
• use nitrogen pressure that forces high-pressure hydraulic
fluid to operate starter motor.
Gasoline engine starters
• use the gasoline engine to rotate the diesel's flywheel.
• operate by means ofa manually operated friction clutch that,
when engaged, causes the starter's pinion to mesh with the
diesel's ring gear on the flywheel.
Compressed-air starters
• are arranged so that compressed air is injected directly into
the diesel's cylinders.
• use compressed air to move the pistons to build up ignition
pressure.
144
Instruments
For example, they can estimate an engine's load. Suppose the Estimating Engine
engine manufacturer recommends that the exhaust temperature Load
not exceed I,ooo°F (540°C). The pyrometer, however, shows an
exhaust temperature of I,07SoF (580°C). This higher-than-normal
temperature indicates that the engine does not have enough horse
power (kilowatts) to adequately power the load the operator has
put on it. Overloading an engine wears it out faster than normal;
in fact, extreme overload can destroy an engine in a matter of
minutes.
DIESEL ENGINES
Cylinder Temperatures Each engine cylinJer also has a place where the operator can attach
a pyrometer and determine the temperamre in that cylinder.
Should one cylinder reaJ low while the others read high, then the
operator knows that the cylinJer with the low reading is not firing
properly.
On the other hand, shoulJ one cylinder read high while the
others read low, the cylinder with the high reading is doing too
much work; it is overloaded. Overload damages the cylinder.
If the temperature of all the cylinJers, except one with a low
reading, is normal and the manifold temperature is very high, the
operator knows that the cool cylinder is passing raw fuel into the
manifold. The abnoffi1ally high manifold temperature lets the
operator know that the engine is burning the fuel in the manifold.
An abnormally high manifold temperature can shorten the life of
the turbocharger.
Dividing Loads Equa/ly In cases where two or more engines drive the same load, pyrometer
readings of each engine's exhaust temperature indicate whether
one engine is carrying more ofthe load than the others. The higher
the exhaust temperature, the greater the load the engine is carry
ing. When the operator evenly divides the load between the
engines, their exhaust temperatures should be nearly the same.
Oil-Pressure An oil-pressuregauge shows the pressure on the lube oil system at the
Gauges point where the operator installed the gauge. From oil-pressure
readings, operators can find out a lot about how the engine is
running. Either a low-pressure or a high-pressure reading can
point the way to problems in the engine.
Low Oil Pressure If the gauge shows low oil pressure, many things could be wrong.
Among these are dilution of the oil, a low level of oil, a blocked
suction screen, or a bearing failure.
INSTRUMENTS
Oil Dilution
Suppose the oil pressure is nomlally 50 psi (340 kPa) when the
engine is at operating load, speed, and temperahlre. If the oil
pressure gradually drops, diesel fuel may he mixing with the lube
oil and diluting it. Diesel fuel can dilute oil when various engine
parts wear or fail. For example, worn or improperly installed
gaskets or seals can allow fuel to leak past the seal and enter the
engine's oil. The oil pump cannot keep the proper pressure on a
thin, dilute oil.
Bearing Failure
Failure of the engine's bearings also gives a low oil-pressure
reading. Bearing failure is serious. If one of the other problems
cannot be identified as a cause oflow pressure, the operator should
stop the engine immediately and get a mechanic to determine
whether the bearings have failed.
High oil pressure can also be asign oftrouble in a diesel engine. Oil High Oil Pressure
that is too heavy (too viscous) overloads the oil pump, which causes
high oil pressure. Another cause of high oil pressure is a stuck or
improperly adjusted regulating valve. Too much oil pressure can
wash out bearings, much as a high-pressure water jet erodes a sand
bank.
DIESEL ENGINES
Lower-than-NormaJ Oil For example, the coolant temperature may be normal but the oil
Temperature temperature is below normal. Cooler-than-normal oil is undesir
able because it may allow water to condense inside the engine,
which could cause damage. vVhat is more, the cool oil causes
clearance tolerances inside the engine to vary from normal, and
abnormal tolerances can cause premature wear. The lube oil's
temperature should be at least as hot as the minimum temperature
set by the manufacturer.
The outlet temperanlre ofthe coolant indicl tes hO\v much hea t has Inlet Versus Outlet
entered the coolant from friction and burning fuel in the engine, Temperature
whereas its inlet temperamre indicates how mllch heat the coolant
removed. It is important for the operator to install a temperamre
regulator so that the cooling system remo\'es only the necessary
amount of heat. The water should not be cold.
AJI supercharged engines have pressure on the air-intake manifold. Air Manifold
A manifold-pressure gauge reads this pressure and indicates it on a Pressure Gauge
gauge. Under load and at operating speed, manifold pressure is
above atmospheric pressure. The supercharger raises the pressure
of the air going into the engine above that of the atmosphere. The
engine operator should look at the engine manual to determine
what the pressure should read.
Dirty air filters restrict the flow of inlet air, which shows up as a Dirty Air Filters
drop in manifold pressure. The operator should therefore check
and clean the air fi1ters~ If, however, the pressure does not remrn
to normal, the mrbocharger may be malfunctioning. If the mrbo
charger is not working properly, the operator should immediately
notify the engine mechanic to avoid damage to the engine.
149
DIESEL ENGINES
To summarize-
Engine instruments-P)'rometers
• measure the temperature of an engine's exhaust; exhaust
temperature indicates whether engine is overloaded.
• measure the temperature ofeach engine cylinder; low cylinder
temperature indicates an improperly firing cylinder; high
cylinder temperature indicates an overloaded cylinder.
Oil-presszl1'e gauges
• Oil-pressure gauges measure the pressure on the lube oil
system.
• Low oil pressure can indicate (I) diluted oil, (2) low oil level,
(3) blocked suction screen, and/or (4) engine bearing failure.
• High oil pressure can indicate (I) overly viscous oil or (2)
improperly adjusted oil-pressure regulating valve.
Oil-temperature gauges
• Indicate lube-oil temperature.
• Lower-than-nonnal oil temperatures may allow water'to
condense or tolerances to vary.
• Higher-than-nonnal oil temperatures may cause oil to break
down and fail.
Coolant-temperature gauges
• Indicate engine's operating temperature.
• Inlet coolant temperature should be no more than about
7SoF (2 SOC) cooler than outlet temperature; a coolant that
is too cold can crack the engine.
Air manifold-pressure gauge
• Indicates the pressure on the air-intake manifold
• Low manifold pressure indicates (1) dirty air filters or (2)
malfunctioning supercharger (turbocharger).
Tachometers
• Measure engine rpm.
• An engine running too slow can be easily overloaded.
• An engine running too fast can destroy itself or equipment
being powered by it.
T
Alarms and
Shutdown Systems
Should an engine overspeed, one kind of overspeed trip device Overspeed Trip
immediately shuts offthe fuel. Another kind oftrip device shuts off Devices
both fuel and air. Operators should remember not to drop the load
from an engine suddenly, because it may overspeed momentarily
and trip the shutdown device.
The overspeed trip should be checked once amonth to ensure that it Checking Overspeed
is working properly. To check the trip, the engine is unloaded, or Trips
disconnected from whatever device it is driving, and its rpm is
increased to the point at which it triggers the shutdown device. The
required shutdown rpm should be indicated in the manufacturer's
manual. If the trip fails to shut down the engine at a speed within
25 rpm of the manufacturer's specifications, the operator should
not increase the engine's speed in an attempt to make the trip work.
Instead, the mechanic should be informed of the problem.
DIESEL ENGINES
Compounded Engines On rigs where the builders compound two engines, the operator
and Overspeeding should always run both engines in the same gear.lfboth engines do
not run in the same gear, one engine can destroy the other by
overspeeding it. To explain, let's say a rig has two compounded
engines: one running in high gear, the other running in low. In this
case, the engines run at different speeds to compensate for different
gear ratios. The engine in high gear turns at a lower speed than the
engine in low gear. Since the engines are compounded, the engine
in high gear drives the engine in low gear, causing the engine in low
gear to overspeed. Worse, even though the overspeed shutdown
trips on the overspeeding engine, the engine cannot stop because
the engine in high gear continues to drive it. The result is a
destroyed engine.
Low-Oil Pressure Most rig engines have low-oil pressure alarms. The alarm is usually a
Alarms very loud horn. Ifthe oil pressure drops below apreset amount, it trips
a relay to sound the hom. On hearing an alarm, the operator should
find the cause immediately. It may simply be that the operator needs
to add oil. Ifnot, however, the driller should be notified immediately.
IT the driller decides to remove the load from the engine with low oil
pressure, the load should be quickly added to another engine. Other
wise, a critical rig component may not have enough power.
ALARMS AND SHUTDOWN SYSTEMS
A low-oil pressure shutdown works in conjunction with the low-oil Low-Oil Pressure
pressure alaml. The operator should set the shutdown to activate at Shutdowns
apressure lower than the alarm. This lower setting gives the operator
time to remedy a malfunction. For example, if the engine's normal
operating oil pressure is 60 psi (415 kPa), the alarm may sound when
the oil pressure falls to 35 psi (240 kPa). Then, when the pressure falls
to 25 psi (170 kPa), the shutdown activates. In this case, the engine
continues to run at 25 to 35 psi (1 7oto 240 kPa) and the alann sounds.
But should the pressure fall below 25 psi (170 kPa), the shutdown
device stops the engine and prevents damage to it.
The engine operator should turn offthe low-oil pressure alarm and Engine Start-up with
shutdown when starting an engine; however, these should be Low-Oil Pressure Alarms
turned back on when the oil pressure reaches normal. This usually' and Shutdowns
takes only about 30 seconds.
Most engines include a cutoff valve in a pressure line that runs to Testing Low-Oil Pressure
the alann and shutdown solenoid. By closing the cutoff valve, the Alarms and Shutdowns
operator can test the alarm and shutdown devices. The closed
cutoff valve disables the alarm and shutdown but does not affect
engine oil pressure. To make the test, the operator unloads the
engine and closes the cutoff valve. The alarm should sound first;
then, as cutoff valve pressure continues to drop, the shutdown
should stop the engine.
153
DIESEL ENGINES
Engine Shutdown Under most circumstances, cutting offthe flowofairto adiesel engine
stops it. Also, cutting off the fuel supply can stop it. Sometimes,
Considerations
however, simply cutting off the fuel is not enough.
Turbochargers and Oil Natural gas is not the only fuel that can enter with inlet air. On a
turbocharged engine, an oil seal separates the lubricating oil from the
intake air. If this seal leaks, the oil pump feeds oil into the intake air,
and the resultingoil-and-airmixture fuels the engine. In this situation,
shutting off the normal fuel supply does not stop the engine.
Using COz to Stop [f an engine does not have an air-shutoff valve and the operator
an Engine must cut off the air supply to stop the engine, the operator can use
acarbon dioxide (C0 2) fire extinguisher. Spraying CO 2 into the air
intake inlet displaces the oxygen in the air, and the engine stops
firing. Under no circumstances should the operator use a dry
chemical extinguisher. This will damage the engine.
154
ALARMS AND SHUTDOWN SYSTEMS
To summarize-
Most engines have nL'O alarms
• low oil pressure
• high coolant temperature
Most engines have three shutdown devices
• low oil pressure
• high coolant temperature
• overspeeding
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155
Engine Operation
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I. All moving parts of the engine should be examined for Prestart Checks
proper adjustment, alignment, and lubrication. Parts to
check include valves, cams, valve gear, fuel pumps, fuel
injection system, governor, lubricators, oil and water
pumps, and the main machinery being driven by the
engme.
2. The engine and machinery should be examined for loose
3. All pipes, valves, and ducts that carry fuel, oil, coolant, or
been idle for some time and is about to be put into service,
157
DIESEL ENGINES
After completing the prestart check, the operator can start the Start-Up
engine, following these steps:
I. With air or hydraulic starters, the main starting valve is
manufacturer's manual.
of the crankshaft.
159
DIESEL ENGINES
Engine Warm-Up
After starting an engine, the operator must nm it at the conect rpm
in order to warm it up. The engine should not be run on idle to warm
it up. An engine turning at idle speed does not hum enough fuel in the
cylinders to heat the engine at an even rate. Cneven heating causes
water to condense and collect in the crankcase. \Vatcr in the crankcase
gets into the oil, mixes with sulfur and other contaminants, and fonns
a damaging sludge. Moreover, because of poor comlmstion when a
cold engine is idling, the fuel does not burn completely. ThnlJ1burned
fuel gets past the piston rings and dilutes the lubt.: oil. Eventually, the
piston rings glaze (build up very hard deposits), which causes excessive
oil consumption and blow-by.
The proper speed for an engine is between idling and full-rpm
speeds. For example, if the engine normally runs at 2,000 rpm, a
good warm-up speed is 1,000 to 1,300 rpm.
Warm-Up Speeds
The engine should reach op~rating temperature as quickly as
possible, because cold oil cannot flow well enough to lubricate all
the parts. Operators can do just· as much harm, however, by
running an engine too fast at start-up as by idling it for warm-up.
Manufacturers make pistons from aluminum. As it heats up,
aluminum expands almost three times faster than the iron in the
engine block. Since the expansion rates are different, severe dam
age occurs to the pistons and block if an operator starts an engine
and immediately runs it at high speed.
In a fast-running engine, the burning fuel contacts the top of
the piston but does not contact a large area of the cylinder. The
aluminum piston readily absorbs the heat ofignition; and as it does
so, it expands. Unfortunately, the metal in the cylinder does not
absorb heat at the same rate as the piston. As a result, the piston
expands faster than the metal surrounding it and therefore enlarges
before the cylinder does. Breaking through the oil film, the piston
makes metal-to-metal contact with the cylinder wall. Metal-to
metal contact creates frictional drag, which generares such a high
heat that it welds small bits ofthe piston to the cylinder wall. When
the piston rings pass over these rough spots, the roughness dam
ages the piston rings.
r60
ENGINE OPERATION
161
DIESEL ENGINES
Putting an Engine Once the engine is properly warmed up, operators can put it to
work. To properly load an engine, however, they must take into
to Work
account what the engine is driving.
Engines Driving a If the engine drives a generator, the loading procedure is a little
Generator more complicated. The procedure varies, depending on whether
the system produces alternating current or direct current. In either
case, before starting the engine, operators should check the gen
erator to make sure it is not connected to any electric load. If in
doubt, they should consult with the rig electrician to determine the
settings of all breaker switches and current relays before starting
the engine or loading the generator.
Although many AC generators do not have rpm gauges (ta
chometers), itis critically important to monitor engine speed. Most
AC generators in the U.S. produce 60-megahertz (MHz) current.
A frequency meter measures and displays this current; it also
regulates the engine's speed. Unforhmately, the frequency meter
may indicate 60 MHz, not only at the proper rpm, but also at a
lower rpm. If the meter does indicate 60 MHz at a low rpm, the
engine may be overloaded because it has not reached its proper
operating speed. Operators should, therefore, use a hand tachom
eter to determine the engine's actual rpm.
On a DC generator, operators should check engine speed with
a tachometer each time they switch the generator to carry a load.
ENGINE OPERATION
While the engine is nmning, the operator must stay on the lookout Checks to Make
for leaks in the cooling system, in the injection valves, and in the
While Engine Runs
air valves. Some leaks may not show up until a part has fully
expanded, after the engine has been operating for a time with a
normal load. No leaks of any kind must be permitted; ifleaks do
occur and cannot be corrected with the engine running, then the
engine must be stopped while repairs are made.
In general, the operator should use the same procedures to
check the engine while it is running under load as those used during
warm-up. The operator should, however, observe the engine on a
regular basis as it runs-for example, every half-hour. These
regular observations should be made even if the engine has auto
matic alarms installed on it, and the readings should be entered in
an engine report.
DIESEL ENGINES
To summarize
Prestart p1'Ocedures
• Check all parts for proper adjustment, alignment, and lubrica
tion.
• Check for loose parts.
• Check for clogged fuel, oil, and coolant lines, as well as clogged
air ducts.
• Check for proper oil level.
• Check the cooling system.
• Check the fuel system.
• Turn the engine over manually if it has been out of service
for a long period.
• Check the starting system.
• Ensure that the engine is not connected to a load.
Start-up steps
• Activate the starting valve or switch.
• When engine starts, shut off the starter motor.
• Ifthe engine fails to start, stop turning it over and correct the
problem.
Warm-up procedures
• Do not idle engine to warm it up.
• Run the engine at one-half its rated speed.
• Check combustion and firing order.
• Determine whether fuel pumps are working properly.
• Observe oil pressure and temperature.
• Check exhaust stack fOf normal exhaust.
Loading the engine
• Move clutch lever from disengaged to engaged position.
• Ifdrivinga generatof, make sure the engine is running at the
proper rpm.
Checks while engine runs
• Look for leaks and correct them.
• Observe the engine on a regular basis-every 30 minutes,
for example.
Reports
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readings is noted.
manifold; and
16 5
DIESEL ENGINES
r66
REPORTS
While the engines are running, operators should be alert for Engine Monitoring
unusual sounds or knocks from the engjne. l'hey should also note
whether the oil temperature is non1l31. High oil temperahlres, for
example, indicate that the engine bealings may be overheating. This
suggests worn bearings that could lead to severe damage. Further
more, operators should always make sure that the driller, or any other
person, does not overload an engine. Finally, operators should check
for overloaded cylinders. A cylinder \\~th an exhaust temperahlre
considerably higher or lower than normal is probably overloaded.
If the flow ofoil or coolant stops for any reason, the entire engine,
or perhaps only acylinder or two, overheats. In either case, the engine
should be stopped at once and allowed to cool gradually. Coolant
should never be put into an overheated engine. The sudden tempera
ture change can cause the pistons to seize (stop). Moreover, the
cylinder heads, liners, or exhaust manifold may crack.
Normally, an engine's exhaust should be perfectly clear. If, how Exhaust Monitoring
ever,·the driller overloads an engine, the exhaust may become
visible as light gray smoke. Operators should never operate an
engine for any length of time with a visible or smoky exhaust.
Smoky exhaust may be the result of one or two cylinders behaving
abnormally. Often, an increase in temperature indicates an abnor
mal cylinder. On the other hand, low cylinder temperahlres mean
that not enough fuel is getting to those cylinders and that the other
cylinders are overloaded. If possible, the operator should stop the
engine, find the cause, and fix it.
To summarize-
Items recorded on engine logs
• Time
• Engine load
• Engine speed
• Fuel consumption
• Exhaust temperature and color
• Lubricating oil pressure and temperaulre
• Coolant temperature
• Scavenge air temperature and pressure
• Supercharger condition
• Air temperature
• Remarks
Engine monitoring
• Be alert for unusual sounds.
• Check oil temperature.
• Check cylinder temperatures for overloaded cylinders.
• Coolant flow.
Exhaust monitoring
• Check for color of exhaust-it should be clear.
• Check for smoke.
Maintenance schedules
• Maintain engine according to schedule.
• Workout schedule according to manufacturer's and owner's
recommendations.
168
ELECTRIC POWER
Introduction
17 1
DIESEL ENGINES
Advantages of AC vVhen it comes to genera ting eleetrici ty, AC gen era tors are better than
Generators
DC generators. Since most of today's rigs still have DC motors, it
might at first glance seem inefficient to generate AC power and rectify
it to DC, compared to generating straight DC power. However,
generating AC power and rectifying it to DC has advantages. For one
thing, rig equipment needs a lot of horsepower (kilrrwatts) to operate.
Because of the way AC generators work, manufacturers can build AC
generators bigger, cheaper, and more powerful than DC generators.
As a result, rig owners can use more powerful diesel engines to drive
the big AC generators, which means that they can use fewer engines
and generators to power the rig. Power costs are thus reduced.
For another thing, many small motors on the rig, plus the rig's
lighting, require AC power. If the rig generates DC power, then the
rig owner must use alLxiliary AC generators for the lights and motors.
With AC generators, the rig does not require auxiliary generators.
Because they do not use corrunutators, AC generators require less
maintenance than DC generators. Commutators are rotating seg
mented rings that tend to wear out the brushes that touch them. Since
manufacturers use acontinuous ring in AC generators, the brushes do
not wear as fast.
DC Generators
Since many DC-to-DC rigs are still in operation, they are worth
studying. Figure 71 diagrams the operation ofasimple DC generator.
Arectangular loop ofstiff copper wire rotates between the north and
south poles of an electromagnet that creates lines of force called
magneticflux. These lines of force flow from the magnet's north pole
on the right to the south pole on the left. Parallel dashed arrows show
the magnetic flux flowing between the two poles.
As the loop rotates through the magnetic flux, it generates electric
current. Each end ofthe loop connects to a commutator. The simple
commutator in the schematic diagram is composed of two segments
ofcopper; in reality, commutators are made up ofdozens ofsegments.
Each half of the commutator segment in figure 7I rotates against a
brush-a small, flexible barmade ofa material that conducts electricity.
The brushes conduct electricity to a circuit outside the generator. In
figure 7 I, the current flows to a meter. The meter's pointer deflects to
the right to show current flow.
In figure 7lA, the black side of the loop is moving up, while the
white side is moving down. Current flows clockwise through the
loop. It goes to the commutator segment on the right, through the
brush, and to the meter. The pointer on the meter shows that
current is flowing.
GENERATORS AND ALTERNATORS
WIRE---....,
METER--~
173
DIESfL ENGINES
STATOR WINDING
l\DC FROM
JlEXCITER
LAMINATED
DISK CORE
COMMUTATOR
SHAFT
ARMATURE WINDING
174
GENERATORS AND ALTERNATORS
A ROTATION
~
METER - - - - - '
ROTATION
B
~
CURRENT FLOW
METER - - - - - '
175
DIESEL ENGINES
To summarize
Generators and Alternators
• Generators change mechanical power to electrical power.
• Modern rigs use AC generators (alternators).
• AC generators are bigger, cheaper, and more powerful than
DC generators.
DC Electric Drive
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cal power and then back into mechanical power may seem hke a Electric Drive
177
ELECTRIC POWER
Exciters
The rig builder mounts a small DC ~enerator, called an exciter, on
or near the main generator. vVhether the exciter is run by an engine
or an outside source, it puts out direct current. This current goes
to the stator in the main generator to produce the electromagnetic
field. The driller then varies the output of the exciter from the
console on the rig floor. By varying the exciter's output, the driller
controls the strength of the magnetic field. The stronger the
magnetic field of the generator, the more current the generator
puts out to drive the load.
Running Engines at On one type of DC-DC electric rig, the engines nm at a constant
speed. This constant engine speed runs the exciters at a constant
Constant Speed
speed. The driller varies the current from the exciter by using a
rheostat. (A rheostat is a variable resistor that controls the amount
of current flowing in a circuit.) The driller adjusts the rheostat to
control resisrance in the flow of electricity going to the generator's
electromagnetic field. A lower resistance allows more current to
flow. The more current the exciter delivers, the stronger the field
in the generator, and the more current the generator puts out to
drive the load.
Running Engines at On another type of DC-DC electric rig, the driller valies the speed
ofthe engines. Varying engine speed varies the speed ofthe exciter,
Varying Speeds
which, in turn, varies the strength of the generator field. In this
setup, the same engine that drives the generator also drives the
exciter.
DC ELECTRIC DRIVE
Aschematic diagram of a typical DC-DC control hookup (fig. 75) DC-DC Schematic
shows two ways to generate electricity. At the top of the drawing
Engine I drives generators 1 and 2, while Engine 2 drives genera
tors 3 and 4. In this case, the driller holds the engine speeds
constant. The scalloped lines just below each generator represent
the windings in the exciter. The "half-clock" symbois next to them
represent the rheostats that vary the flow of current from the Figure 75. Control hook
exciters to the generators. The small white rectangles below the up of DC electric drive,
rheostats represent the air actuators or electric act1lators that typical except for air throttle
operate the rheostats. rather than more common
elect1-ic throttle
MOTOR
..---t---t----t--- CONTACTOR
(OPEN)
DRAWWORKS
~- (CLOSED)
I--(...........-=;...;....---.........;;I:....-~"""tdf---+-'-i--+-......L.+-.........jf----'
AIR THROTTLE
'----t--+--+---t--+--t- SOLENOID.OPERATED
ELECTRICAL AIR VALVE
CONTACTOR
(OPEN) :::..
lPl
4Pl
PUMP 1
PRESSURE SOLENOID·
SWITCH OPERATED
AIR VALVE
2P2 T 4P2
2P2 4P2
PUMP2
PRESSURE
SWITCH
ELEGRIC POWER
180
DC ELEGRIC DRIVE
® ®
( G_E_N_E_RA_T_O_R_N_O_.1_ _ ~)
OFF
Figure 75 provides an example ofassigning power. Note the closed Assigning Power
electrical contaL1ors indicated by small black rectangles. With
contactor ID closed, the driller assigns power from generator I to
drive the rotary table. With contactors 2 P I and 3P I closed,
generators 2 and 3 drive mud pump no. I. With contactor 4P2
closed, generator 4 drives mud pump no. 2.
181
ELECTRIC POWER
Using the Throttles Still referring to figure 75, note the three air throttles on the left.
To start the rotary table, the driller advances the air throttle
controlling the drawworks and rotary table. The initial air pressure
in the throttle line causes the drawworks pressure switch to (I) close
the contactor on the line from generator I, (2) open the solenoid
operated air valve in the air line, and (3) close the other air valves.
Further advancement of the air throttle increases the magnetic
field in the generator in direct relation to the movement of the
throttle handle, and the rotary begins to turn at the speed set on the
air throttle. Similarly, the driller uses an air thronle to start
generators 2 and 3 and adjust the speed of pumps I and 2.
Driller's Control Except for the assignment switches and the speed controllers, the
Panel driller's control panel contains air controls like those on a mechani
cal rig (fig. 78). Other devices on the control panel include an
ammeter for each motor. An ammeter measures the amount of
electrical current produced by the motor in units called amperes
(amps). Since the amperage put out by the motor translates into
torque, the driller can use the ammeter to measure the torque each
motor develops.
A voltmeter on the panel indicates engine speed by measuring
electrical voltage. Voltage is somewhat like the pressure on fluid
flowing in a pipe. In the case of electricity, voltage is electrical
force. The higher the voltage in a circuit, the higher its electrical
force. And, the higher the electrical force, the faster the engine
runs.
The panel also includes a reversing switch for the drawworks
and rotary, an emergency stop button, and indicating lights. As
mentioned earlier, the panel also has an assignment switch for each
generator.
182
.'!i:, .'
, .,}'
f .. '
.~.'
,,/
•••£
Main Control A control cabinet houses most of the electric and pneumatic
Cabinet controls for a DC-DC drive. Cables come out of the control
cabinet and carry the circuits necessary to control the rig. All the
electrical connections are of the plug-in type. \iVhen rigging up,
personnel lock the connections in place to prevent them from
disconnecting (fig. 79).
The control ca binet also houses all the safety devices needed to
shut down a circuit in case of a short, overload, or damaged cable.
Interlocks set up a sequence of events that prevents damage to, or
operation of, equipment should someone engage the wrong oper
ating lever.
A ground relay shuts off power if a cable is damaged and sends
electricity through any structure that is not part of the electrical
system. This system prevents electrical shock to operatingperson
nel during normal operations. It is, however, vitally important to
follow proper lock-out and tag-out procedures when maintaining or
repairing any of the equipment.
Din and dust are the enemy of all electrical equipment, so the Maintenance
equipment must be kept as clean and as dust free as possible. Din
collects moisture, which causes short circuits and binding of
moving parts. Oil and grease are good dirt collectors, so they
should be kept away from electrical equipment. Following the
manufacturer's recommendations when greasing generator or
motor bearings is very important for proper maintenance.
A lintless cloth is the best medium for cleaning large equip
ment. Dirt may also be blown away with dry compressed air. If it
becomes necessary to use a solvent, the operator should make sure
that the solvent is approved for electrical equipment; some solvents
dissolve insulation. Water should never be used to clean electrical
equipment. Materials dissolved in even the cleanest water conduct
electricity and cause short circuits. Everyone who works around
electrical equipment should keep in mind that water and electricity
do not mix.
Asmall paint bmsh serves to brush dirt from small equipment.
Once the dirt is bmshed off the equipment, avacuum cleaner may
be used to remove it. Dirt should not be allowed to fall into contacts
and armatures.
No oil or grease should be used on a commutator, whether it
is part ofamotor or agenerator. Acommutator operating normally
has a film on it, but this film never needs oiling. Grooved or
streaked commutators should be repaired or replaced.
Burned or broken bmshes in a generator or motor mean that
the commutator is out of round or has high or low commutator
bars. Crew members must pull such a unit and send it to a repair
shop. Most likely the shaft is bent or the motor has been over
heated.
18 5
ELEGRIC POWER
INSULATION
)/' PORCELAIN
~ COMMUTATOR
TOTAL SURFACE
CURRENT
IN
SCR Systems
Diesel-electric rigs using diesel engines to power DC generators,
which, in hIm, powered DC motors, were the first on the scene. In the
late 1960s, when transistors and other solid-state electronic devices
came into their own, rig designers and manufachlrers began to
develop other ways to transmit and control electric power. They
began using diesel engines to turn AC generators, converting or
rectifying the AC to DC, and using the DC to power motors on the
equipment. Solid-state devices called silicon-controlledrectifiers (SCRs)
rectify AC to DC. SCRs are also called Thyristors.
186
DC ELEGRIC DRIVE
FULL v.. Y2 %
POWER POWER POWER POWER SINE WAVE
A I
o
I : I
f\ l i \ C\ (\
C l V \ J V\J~~~E
I
r
Figure 81. DC voltage shown as a sine wave
ELECfRlC POWER
1ft he driller makes the SCR conduct electricity all the time, the
SCR relays full current in only one direction, thus converting AC
tn DC;Jt maximum power capacity. The sine wave diagrammed in
tlg-ure HI indicates maximum power if DC flows the entire time the
wave is above the base line. If, howeytr, the driller makes the SCR
conduct during only pan of each sine wave, the SCR converts and
transmits only part of the current at reduced power. By using a
special controller, the driller can govern the point on the sine wave
when the SCR starts to conduct, and thus vary from zero to
maximum the amount of rectified power relayed to the motor.
,r0 satisfactorily control the gate voltage, the manufacturer has to
combine several input signals. For example, the driller has to be able
to control a motor's power output, so the manufacturer includes a
throttle signal. Other signals fed to the gate-control system include (I)
cmTent-Emit sig11als to limit the ma:ammTI amount of current con
ducted; (2) a rate-limit signal to control the rate of current rum-on,
which minimizes electrical surges; (3) a paralleling signal to allow the
rig operator to flU1more than one SCR in parallel (paralleling SCRs
may be required to power a large motor); and (4) motor speed-limit
signals to prevent the motor from being mn too fast.
AC Bus and
In the SCR (AC-DC) system, standard three-phase alternators
Control Units
generate AC power (fig. 82). The size and type of rig determine
the size and voltage of the alternators. Heavy-duty cables feed
power from the alternators to a common set of conductors.
188
DC ELECfRlC DRIVE
This set of conductors is called the AC bus or the common bus (fig.
83). The common bus is made up of large copper cables, usually
called bus bars. Power from the bus then flows to special units or
cabinets, where the SCRs rectify the AC and where other controls
are located.
ACBUS .. -- . I
ACBUS
. ---- ------------~
LII--- • -.
I
1r I -.
,---'--
I!!L.:tl.Jvut1I
-. \I r- ..--
tJ _
DRILLER'S CONSOLE :
-
~-+:
r- r-
I ==
r- r-
.:::::~
"----
-() I MOTOR OW FIELD SUPPLY
MUD I GENERATOR 1SCR UNIT XF MR FEEDER CONTROL DYNAMIC UNIT CABINET
PUMP/CEMENT
PUMP CONSOLE
I UNIT CABINET
" .. - - - - - - - -
CABINET
- - - - - - - - - - - - - - ,
4 AC BLOWER •
J :
• CENTER BRAKE
I
I
......1 - - - POWER I
... - - - CONTROL
. ~---------_ . I
DC FIELD
Meeting Power Each motor on an AC-DC electric rig usually drives a load that is
Needs different from the load on other motors in the system. In other words,
each motor's load is unique to that motor. The manufacturer provides
a device called an SCR converter that a technician can set to provide
the proper voltage and power for each of the different loads. But each
motor must have its own SCR converter, and if the driller needs to
power six motors at the same time, the system has to have at least six
SCR converters. By using switches or contactors, the rig owner can
vary the combinations ofmotors and SCR converters so that a diverse
number of load requirements may be met with ease.
In operating an SCR rig, the system has to generate only
enough AC power to meet the total DC-motor demands at any
particular time. Good practice, however, calls for keeping a little
surplus AC capacity. The rig may need this extra capacity when
some operation suddenly requires more DC power. Usually, the
rig owner can predict fairly accurately what the power demands
will be for each operation in the drilling project. As a result, rig
owners do not have to run all ofthe AC generators when they know
that aparticular operation requires less power than the system's full
capacity. This economy, along with the ease and flexibility of
control, is the real advantage of the SCR system.
Because it is so important that all engines and AC generators carry Electronic Governors
equal shares of the load, the manufacturer installs very sensitive
and accurate engine governors. Rig technicians should keep a close
eye on the governors to ensure that they are working correctly to
keep the engine speeds constant. The technician can manually
adjust the governors if necessary.
When the total load on the engines is relatively constant, the
technician can easily adjust each engine governor so that each
generator set carries its share of the total load. When a rapid and
great change in load demand occurs, however, the ~ystem may be
fully loaded at one instant and nearly unloaded at the next. To meet
such emergencies, SCR rigs use integrated, electronically con
trolled governors on each engine. Electronic governors sense the
output current of each generator and automatically and rapidly
adjust engine speeds to ensure that each engine carries an equal
share of the load.
Rig operators need to take care when adding or removing AC Adding or Removing
generators from the line. As emphasized above,· all generators Generators from the Line
connected to the common bus must run at identical or synchronous
speed. If they do not run at synchronous speed, any "out-of-sync"
generators can be severely damaged or destroyed. When a genera
tor is said to be nmning at synchronous speed, this means that it
may be running faster or slower than other generators, but it is
running in cycle with them. That is, its electrical output is in phase
with the other generators. The sine waves produced by generators
running "in sync" all match.
In any case, when rig operators put an additional generator on
line, they must either bring it up to the exact speed of the other
generators or bring it to a speed that synchronizes it with the other
generators, before they close the switch connecting it to the bus.
The following steps should be taken to bring an AC generator
on-line.
I. The engines are started and allowed to warm up.
193
ELECTRIC POWER
Auxiliary Power Supply Mechanical and DC-DC rigs require auxiliary equipment to
generate AC power. AC provides rig lighting and runs several
small motors on the rig. (Recall that SCR rigs, since they generate
AC, do not require auxiliary AC power generation equipment.)
The total AC electrical power requirements for the auxiliary
equipment on a small-to-medium-size land rig may not be more
than 100 kW. Rigs usuaJly have enough AC generating capacity to
provide twice the amount of power required. Having twice the
power required means that the rig has 100 percent standby gener
ating capacity. That is, if half the generators failed, the rig would
still have enough power to generate full capacity. Table 1 shows
some of the main items requiring AC power on a land rig.
Table I
AC Power Required By Rig Equipment
Electric lighting 12
Shale shaker 5
(two 3-hp or 2.1-kW motors)
Mud-tankagitators 30
(four 1o-hp or 7-kW motors)
Desander, centrifugal pump 25
(35 hp or 24·5 kW)
Degasser and centrifuge unit 10
(12 hp or 84 kW)
Air compressors 20
(2 5-hp or q.S-kW motor)
Bunkhouse cooling and heating S
BOP accumulator unit IO
I94
DC ELECfRJC DRIVE
To summarize-
DC-DC Electric DTive
• Diesel engines drive DC generators.
• Cables and switch gear carry DC power to DC motors on
equipment.
• Driller can run engines at constant speed or at different
speeds.
Rules joT Maintenance
• Keep equipment clean.
• Blow dirt away on large equipment.
• Brush away and vacuum dirt on small equipment.
• Do not use water to clean.
• Check connections for tightness when rig is shut down.
• Do not use grease or oil.
SCR Systems
• Diesel engines drive AC generators (alternators).
• Silicon controlled rectifiers (SCRs) or Thyristors convert
(rectify) AC to DC.
• DC motors are mounted on equipment to be powered.
• All engines should be run at the same speed.
• All AC generators should be run at the same or synchronous
speeds.
Glossary
....
....
....
AC bus n: in a diesel-electric power system, a common set of conductors made A
up of large, heavy-duty copper cables that carry alternating current generated
by the system's alternators (AC generators).
acid corrosiveness n: a characteristic of diesel fuel that indicates the likelihood
ofa diesel fuel's causing corrosion as the engine burns fuel. In general, a fuel with
a high acid content will be more corrosive than a fuel with low acid content.
aftercooler n: on a supercharged engine, a device, cooled by either air or by,
engine coolant, that reduces the temperature of the engine's exhaust. It is
necessary to cool the exhaust's temperature because the exhaust drives the
supercharger, which forces air into the engine's intake manifold. The tempera
ture ofthe supercharged air must be at an acceptable level; otherwise, the engine
will run too hot. See supercharger. .
air intake manifold n: on a diesel engine, an arrangement of pipes and
passageways through which air is conducted to the engine's combustion cham
bers.
air knocking n: on a diesel engine, a phenomenon that occurs when trapped air
in the fuel injection system enters the engine's cylinder with the fuel. The fuel
air mixture ignites but, because of the extra air in the fuel, the engine cylinder
misfires and knocks or hammers. The problems should be corrected promptly
to prevent damage to the engine.
air-motor starter n: on an engine, a device powered by compressed air that
starts the engine. The compressed air, when allowed to enter the starter motor
by means of avalve, causes a gear on the starter to engage a gear attached to the
outer edge ofthe engine's flywheel. The rotating starter gear moves the flywheel
gear, which causes the engine's pistons to move. If fuel, air, and, on spark
ignition engines, an electric spark are present in the engine, the engine will start
after a few rotations. As soon as the engine starts, the starter gear disengages
from the flywheel gear. Air-motor starters are installed on large 'industrial
engines like those used on a drilling rig.
air shutoff valve n: on a diesel engine, a special valve that, when activated,
prevents air from entering the engine's combustion chambers, thereby stopping
the engine. Air shut-offvalves are asafety feature that may be needed when awell
blows out. Ifnatural gas is present in the blowout's fluids, adiesel engine can take
in the gas and continue to run even when its normal fuel source is cut off.
alternating current (AC) n: current in which the charge-flow periodically
reverses and whose average value is zero. Compare direct current.
alternator n: an electric generator that produces alternating current.
DIESEL ENGINES AND ELECTRIC POWER
ampere (A) 11: the fundamental unit of electrical current; 1ampere = 6.28 x IOI8
electrons passing through the circuit per second. One ampere delivers 1 coulomb
in I second.
annular blowout preventer 11: a large valve, usually installed above the ram
preventers, that forms a seal in the annular space between the pipe and the
wellbore or, if no pipe is present, in the wellbore itself. Compare ram blowout
preventer.
antifreeze n: achemical added to liquid that lowers its freezing point. Often used
API gravity n: the measure ofth'e density or gravity ofliquid petrolelilll products
in the United States; derived from relative density in accordance with the
following equation:
bag filter 71: on an engine, a b3g-~haped piece IJl3de of cotton or fiber cloth that
fits into a special holder in the fuel system piping. Fuel is circulated through the
b3g, which removes foreign ll1,ltter from the fuel.
ball bearing 7l: a be;lrin~ in which a finely 1l13chined shaft (a journal) turns on
freely rotating hardened-steel spheres that roll easily within a groove or track (a
race) and thus comcn sliding friction into rolling friction. See ball race.
ball race 11: a trac],;, channel, nr groove in which ball bearings turn.
bar v: to move or turn (,lS ,1 fl:"wheel) with 3 bar used as 3 lever.
battery n: J. 3n install3tion of identical or nearly iJentical pieces of equipment
(snch as a tank battery or a battery of meters). 2. an electricity storage device.
BDC ahbr: bottom dead center.
Bendix n: the brand name for a type of friction dutch in an electric starter for
small engines. When electric current is applied to the starter, the friction clutch
(the Bendix) moves forward to engage apinion gearon the starter with aring gear
on the engine flywheel. As the starter's pinion rotates, it rotates the ring gear,
. blow-by n: the percentage of gases that escape past the piston rings from the
combustion chamber into the crankcase of an engine.
blowout n: an uncontrolled flow of gas, oil, or other well fluids into the
atrrio~phere. Ablowout, or gusher, occurs when formation pressure exceeds the
pressu:re applied toit by the column ofdrilling fluid. Akickwarns ofan impending
blowout. See kick.
blowout preventer n: one of several valves installed at the wellhead to prevent
the escape of pressure either in the annular space between the casing and the drill
pipe or in open hole (i.e., hole with no drill pipe) during drilling or completion
operations. Blowout preventers on land rigs are located beneath the rig at the
land's surface; on jackup or platform rigs, at the water's surface; and on floating
offshore rigs, on the seafloor. See annularblowoutpreventer, ram blowoutpreventer.
booster pump n: on a diesel engine, a small manually or electrically operated
pump that an engine operator can use to prime the engine's fuel system for
starting the engine. When activated, the pump moves fuel from a tank, through
the engine's fuel lines, and to the engine's injectors, ensuring that fuel is available
for starting the engine.
bottom dead center (BDC) n: the positioning of the piston at the lowest point
possible in the cyIinde.r of an engine; often marked on the engine flywheel.
breather n: a small vent in an otherwise airtight enclosure for maintaining
equality of pressure inside and outside.
brush n: a carbon block used to make an electrical connection between the rotor
of a generator or motor and a circuit.
bus n: an assembly of electrical conductors for collecting current from several
sources and distributing itto feeder lines so that itwill be available where needed.
Also called bus bar.
bus bar n: see bus.
bypass valve n: a valve that permits flow around a control valve, a piece of
equipment, or a system.
DIESEL ENGINES AND ELECTRIC POWER
200
GLOSSARY
201
DIESEL ENGINES AND ELECTRIC POWER
cutoffvalve n: a special valve on an engine that, when activated, blocks the flow
of fuel to the engine to make it stop running.
cycle n: the number of strokes a piston makes from one intake stroke to another
intake stroke. Diesel engines may have either two strokes or four strokes per
cycle.
o
(such
demand the quantity ofoil, gas, or other petroleum products, or commodities
n:
as electricity) wanted at a specified time and price.
detergent n: in lubricating oils and in some engine fuels, a chemical that is added
to the oil or to the fuel that suspends dirt, carbon, and other foreign matter in the
oil or fuel. As a result of the detergents in motor oil, the oil will very quickly
appear dirty because it is suspending the particles.
diesel engine n: a high-compression, internal-combustion engine used exten
sively for powering drilling rigs. In a diesel engine, air is drawn into the cylinders
and compressed to very high pressures; ignition occurs as fuel is injected into the
compressed and heated air. Combustion takes place within the cylinder above the
piston, and expansion of the combustion products imparts power to the piston.
diode n: I. an electronic device that restricts current flow chiefly in one direction.
2. a radio tube that contains an anode and <1 cathode.
202
GLOSSARY
radiation.
distillationn: the process ofdriving offgas orv:1por from liquids or solids, usually
by heating, and condensing the vapor back to liquid to purify, fractionate, or form
new products.
distributor n: a device that directs the proper flow of fuel or electrical current to
the proper place at the proper time in the proper amount.
dry air cleaner n: on an engine, a device that contains an air filter element that
does not depend on oil to effectively filter th~ air entering the engine. Instead, the
filter element has a number of folds and chambers that trap dust and dirt going
into the engine's air intake. Some dry elements may be cleaned and reinstalled;
manipulating aremote control, the engine operator can adjust the electric motor
electric startern: a device that uses a battery, an electric motor, gears, and cables
engine over by means of a pinion gear in the starter that engages a ring gear on
positive and negative ions, thus increasing its electrical conductivity. See dissocia
tion. 2. the electrically conductive solution that must be present for a corrosion
cell to exjst.
engine n: a machine for converting the heat content of fuel into rotary motion
that can be used to power other machines. Compare motor.
engine temperature switch (ETS) n: a device on an engine that senses
overheating and shuts down the engine if overheating occurs.
exchanger n: a piping arrangement that permits heat from one fluid to be
transferred to another fluid as they travel countercurrently to one another. In the
heat exchanger of an emulsion-treating unit, heat from the outgoing clean oil is
transferred to the incoming well fluid, cooling the oil and heating the well fluid.
In the heat exchanger of a glycol dehydration unit, heat from the hot lean glycol
flows through the inner flow tube in the opposite direction ofthe cool rich glycol,
which flows through a shell built around the tube.
exciter n: a small DC generator mounted on top of a main generator to produce
the field for the main generator.
2°3
exhaust 17: the burned gases that are removed from the cylinder uf an engine. v:
to remove the burned gases from the cylinder of an engine.
that collects burned gases from the engine and channels them to the exhaust pipe.
exhaust pipe n: on an engine, flexible steel tubing that connects the engine
exhaust manifold outlet to the muffler. See muffler.
exhaust silencer n: see muffler.
exhaust stroke n: in an engine, the movement of the piston during which time
fin n: a thin, sharp ridge around the box or the pin shoulder ofa tool joint, caused
by the use of boxes and pins with different-sized shoulders. See radiator fin.
engine. For example, in an eight cylinder engine, the firing order could be 1-8
4-3-6-5-7-2, which means that combustion occurs first in the fi rst cylinder, then
in the eighth cylinder, and so on, until combustion occurs in the second cylinder;
weights that spin as the engine runs. When the engine speeds up, centrifugal
force on the spinning flyweights increases, which causes a spring to compress and
slow the engine down. Conversely, when the engine slows down, centrifugal
force on the flyweights decreases which causes the spring to expand and speed the
engme up.
2°4
GLOSSARY
four-stroke/cycle engine n: an engine in which the piston moves from top dead
center to bottom dead center two times to complete a cycle of events. The
fuel centrifuge n: a device an engine operator uses to separate water and solid
materials from fuel. Centrifugal force created by the rapidly spinning centrifuge
causes dirt and water, which are heavier (denser) than fuel, to move to the outside
fuel injector n: a mechanical device that sprays fuel into a cylinder of an engine
fuel knock n: a hammerlike noise produced when fuel is not burned properly in
a cylinder.
fuel modulator n: a device installed on a diesel engine to reduce the amount of
smoke coming out ofthe engine's exhaust. If the engine's governor delivers more
fuel than air to the engine, the engine smokes too much. Afuel modulator makes
the governor increase the fuel supply only atthe same rate as the air increase. Such
rate control holds down the black smoke from the engine exhaust during
acceleration or sudden loading. See governor.
fuel pump n: the pump that pressurizes fuel to the pressure used for injection.
In a diesel engine the term is used to identify several different pumps: it is loosely
used to describe the pump that transfers fuel from the main storage tank to the
day tank; it is also used to describe the pump that supplies pressure to the fuel
injection pumps, although this is actually a booster-type pump.
fuel transfer pump n: any relatively small pump in an engine's fuel system that
moves fuel from one fuel tank to another or from a tank to another location in
the fuel system.
gasket n: any material (such as paper, cork, asbestos, or nlbber) used to seal two G
that runs on spark plugs and gasoline and whose power is used to turn over (move)
the pistons in the diesel. As the diesel's pistons move, pressure and heat builds in
the diesel's cylinders and the diesel starts. As the diesel begins nmning, the
flow in one direction through the SCR. As long as gate voltage is applied, the SCR
voltage is shut off, no electrical current can flow through the SCR.
glow plug n: a small electric heating element placed inside a diesel engine
2°5
H
e.g., a manifold.
hp abbr: horsepower.
to the engine's speed control, a hydraulic governor operates the speed control
with oil pressure inside the governor. See governo1·. Compare mechanicalgovernor.
hydraulic starter n: on an engine, a device used to start the engine that uses
hydraulic fluid under pressure to operate a motor on the starter. When engaged,
the starter motor turns the engine's flywheel to make the engine start.
boiling points, and freezing points increase as their molecular weights increase.
compounds, because ofthe strong affinity ofthe carbon atom for other atoms and
for itself. The smallest molecules of hydrocarbons are gaseous; the largest are
dropped into it. It floats at a certain level in the liquid (high if the liquid is light, low
if it is heavy), and the stem markings indicate the gravity of the liquid.
ignition quality n: the ability of a fuel to ignite when it is injected into the
installed on engines in extremely cold climates, such as in Alaska and Siberia. Before
the engine is started, the switch senses very cold coolant and turns on an immersion
heater in the coolant tank, thus ensuring that the engine warms up quickly.
206
GLOSSARY
impeller n: 3 set of mounted blade~ used to imp.1ft mution to a fluid (e.g., the
rotor of a centrifugal pump).
injection n: the process of forcing fluid intI) ~olll~thing. In a diesel engine, the
injection line n: strong steel tubing that conducts fuel from the fuel tanks to fuel
injectors on the engine.
injector n: a fuel atomizing device th,lt injech (puts) 3 fine spray of fuel into the
injector pump n: a chemical feed pump th:lt injects chemical reagents into a
flow-line system to treat emulsions at a rate proportional to that of the flow ofthe
well fluid. Operating power may come from electric motors or from linkage with
the walking beam of a pumping well.
intake stroke n: the downward movement of ,1 piston in a cylinder that creates
an area of low pressure inside the cylinder. The low pressure draws in air from
the atmosphere (or from a hlower).
intake valve n: I. the cam-operated mechanism on an engine through which air
and sometimes fuel are admitted to the cylinder. 2. on a mud pump, the valve that
opens to allow mud to be drawn into the pump by the pistons moving in the liners.
isochronous governor n: a governor that maintains a constant speed of the
prime mover regardless of the load applied, within the capacity of the prime
mover.
kick n: an entry of water, gas, oil, or other formation t1uid into the wellbore K
during drilling. It occurs because the pressure exerted by the column of drilling
t1uid is not great enough to overcome the pressure exerted by the t1uids in the
formation drilled. Ifprompt action is not taken to control the kick, or kill tile well,
a blowout may occur. See blowout.
kilowatt n: a metric unit of power equal to approximately 1. 34 horsepower.
lead-acid battery n: a storage battery in which the electrodes are grids of lead L
oxides that change in composition during charging and discharging, and the
electrolyte is dilute sulfuric acid.
lifter n: a device in an engine against which a cam rotates as the engine runs. As
the high point of the cam rotates, it pushes against (lifts) the lifter. The lifter, in
turn, actuates a push rod or other d'evice to open a valve or similar device.
Sometimes called a cam follower.
load n: I. in mechanics, the weight or pressure placed on an object. The load on
a bit refers to the amount of weight of the drill collars allowed to rest on the bit.
See weight on bit. 2. in reference to engines, the amount of work that an engine
is doing; for example, 50 percent load means that the engine is putting out 50
percent of the power that it is able to produce. 3. the 3mount of gas delivered or
required at any specified point or points on a system; load originates primarily at
the gas-consuming equipment of the customer. v: I. to engage an engine so that
itworks. Compare idle. 2. to set a governor to maintain a given pressure as the rate
of gas flow through the governor varies. Compare demand.
2°7
magnetic flux 11: energy that flows between the north and south poles of a magnet.
M The magnet may be either natural or it may be an electromagnet, which is created
by applying electric current to a conductor, such as iron or steel. See flux.
main bearing 11: in an engine, a large circular friction-reducing device installed
on the engine's crankshaft. Main bearings are mounted in the engine's crankcase
and the crankshaft rotates on them. Engine oil lubricates them as the engine runs.
Most main bearings are plain bearings, in that their wear surface is flat or plain
and do not have balls or rollers. Compare ball bearing, roller bearing.
manifold 11: 1. an accessory system of piping to a main piping system (or another
conductor) that serves to divide a flow into several parts, to combine several flows
into one, or to reroute a flow to anyone of several possible destinations. 2. a pipe
fitting with several side outlets to connect it "vith other pipes. 3. a fitting on an
internal-combustion engine made to receive exhaust gases from several cylinders.
manifold pressure gauge n: a device installed on an engine's intake manifold
that indicates the pressure inside the manifold. Manifold pressure is a measure of
the airflow into the engine cylinders at a given speed and intake air temperature.'
Thus, when combined with the engine's rpm, manifold pressure is an indication
of the engine's power output.
manometern: aV-shaped piece ofglass tubing containing aliquid (usuallywater
or mercury) that is used to measure the pressure of gases or liquids. When
pressure is applied, the liquid level in one arm rises while the level in the other
drops. A set of calibrated markings beside one of the arms permits a pressure
reading to be taken, usually in inches or millimetres.
(
mechanical governor n: a speed-control device on an engine. Mechanical gover
(
nors consist offlyweights, springs, and mechanical connections to the engine's speed
(
control. Compare electrically-actuated governor, hydraulic governor. See governor.
c
metal-edge strainern: in an engine, a fuel filter that consists ofseveral very thin
metal discs stacked inside a housing. As fuel flows through the strainer, foreign (J
matter in the fuel is trapped by the very small spaces between the discs. h
tI
micropore paper 11: heavy-duty paper perforated with several very small holes
n
(pores). Folded in accordion pleats, micropore paper often serves as a secondary
filter element in an engine's fuel system. Fuel passes through the pores, while the o
unperforated part of the paper stops dirt. el
motor n: a hydraulic, air, or electric device used to do work. Compare engine. o
muffler n: a device installed on an engine to quiet tile barking sound produced eJ
by exhaust gases exiting through the exhaust pipe of the engine. One type of
muffler is a steel cylinder with baffle plates. The baffle plates, flat steel sheets oJ
welded inside the cylindrical body ofthe muffler, change the direction ofexhaust 01
gas flow. Changing the direction of flow allows the gases to expand gradually, n(
rather than all at once. Gradual expansion is quieter than rapid expansion. SIl
Sometimes called an exhaust silencer. an
208
GLOSSARY
multipump injection system n: in a diesel engine, asystem that uses several fuel
pumps to take fuel from a supply tank and send it to the engine's fuel injectors.
The pumps may be separate or combined into a single housing.
oil-bath air cleaner n: on an engine, a canister that has a relatively small amount 0
of lubricating oil in the bottom and which filters air entering an engine. The
running engine draws air through the cleaner, where the air passes through an
element and over the oil bath. Dust and dirt particles in the intake air are removed
by the element and by the oil bath.
oil-bath cleaner n: see oil-bath air cleaner.
oil cooler n: on an engine, a device through which engine lubricating oil is
circulated to reduce its temperature to acceptable levels. Some oil coolers depend
on the surrounding air to reduce the temperature, but on most large engines, the
oil is circulated through tubes that are surrounded by engine coolant.
oil pressure gauge n: a device that shows the pressure of the oil in an engine's
lubricating system. Oil must achieve a certain minimum pressure to move
throughout the engine and to provide an adequate film ofoil around the engine's
moving parts.
oil pump n: a special pump, usually of the gear type, that moves oil through an
engine. The pump's intermeshing gears rotate to build pressure and circulate the oil.
oil temperature gauge n: a device that shows the temperature of the oil in an
engine's lubricating system. Oil whose temperature is too high cannot lubricate
properly.
orifice n: an opening of a measured diameter that is used for measuring the flow
of fluid through a pipe or for delivering a given amount of fluid through a fuel
nozzle. In measuring the flow of fluid through a pipe, the orifice must be of
smaller diameter than the pipe diameter. It is driJ]ed into an orifice plate held by
an orifice fitting.
2°9
p
paraffin n: a saturated aliphatic hydrocarbon having the formula CnH 2n + 2 (e.g.,
methane, CII4; ethane, C2H 6). Heavier paraffin hydrocarbons (i.e., C 1s H 3S )
form a waxlike substance that is called paraffin. These heavier paraffins often
accumulate on the walls of tubing and other production equipment, resu'icting
or stopping the flow of the desirable lighter paraffins.
pigtail n: in the brush holder ofagenerator, a device composed ofseveral braided
copper wires that conduct electricity from a generator's brush to the generator's
wmng.
pinion n: I. a gear with a small number of teeth designed to mesh with a larger
wheel or rack. 2. the smaller of a pair or the smallest of a train of gear wheels.
pipe rack n: a horizontal support for tubular goods.
piston n: a cylindrical sliding piece that is moved by or that moves against fluid
pressure within a confining cylindrical vessel.
piston stroke n: the length of movement, in inches (millimetres), of the piston
of an engine from top dead center (TDC) to bottom dead center (BDC).
plunger n: I. a basic component of the sucker rod pump that serves to draw well
fluids into the pump. 2. the rod that serves as a piston in a reciprocating pump.
3. the device in a fuel-injection unit that regulates the amount of fuel pumped on
each stroke.
positive crankcase ventilation (pCV) valve n: a valve installed on an engine
that, when open, directs gases from inside the engine through piping to the intake
manifold. At the intake manifold, the crankcase gases enter the engine's combus
tion chamber and are burned. Burning crankcase gases in this manner not only
cuts down on air pollution, but also scavenges corrosive fumes from the engine
to prevent sludge from forming.
pour point n: the lowest temperature at which a fuel will flow. For oil, the pour
point is a temperature 5°F (- I SoC) above the temperature at which the oil is solid.
pressure gauge n: an instrument that measures fluid pressure and usually
registers the difference between atmospheric pressure and the pressure of the
fluid by indicating the effect of such pressures on a measuring element (e.g., a
column ofliquid, pressure in aBourdon tube, aweighted piston, or adiaphragm).
210
GLOSSARY
pressure reliefvalve 11: avalve that opens at a preset pressure to relie\'e excessive
pressures within avessel or line, Also called a pop val"e, reliefvalve, safety valve,
or safety relief valve.
pressurized cooling system n: an engine cooling system in which a pressure
tight seal is maintained, usually by a special cap placed on the radiator's opening.
The pressure-tight seal keeps the pressure on the cooling system slightly above
atmospheric pressure. Maintaining pressure slightly above that of the atlno
sphere raises the boiling point ofwater (often the main ingredient in the engine's
coolant), eliminates evaporation ofcoolant from the system, and permits ahigher
operating coolant temperature, which results in more effective heat transfer from
the coolant to the air.
prestart lubrication system n: an assembly of devices, including a special oil
pump that works separately from the engine, that allow an engine operator to
circulate lubricating oil through an engine prior to starting it. Pressuring up the
oil in an engine before it starts ensures that a good lubricating oil film forms on
the engine parts, thus reducing wear on them.
primary pump n: see booster pump.
as pipe. See pipe rack. 2. a bar with teeth on one face for gearing with a pinion or
worm gear. 3. a notched bar used as a ratchet. v: I. to place on a rack. 2. to use as
a rack.
rack-and-pinion gear n: a gear comprising a bar with teeth on one face that
engages with a pinion (a small gear).
radiator core n: on an engine, the tube or tubes through which engine coolant
is circulated. These tubes benu back and forth several times so that the coolant
will have plenty of surface to contact as it flows through them. Very thin metal
plates (fins) are attached to the tube, which radiate heat in the coolant to the
surrounding air.
radiator fin n: on an engine, very thin metal plates that are attached to the
radiator's tubes. Because there are hundreds of these plates in contact with the
surrounding air, they efficiently radiate heat from the coolant circulating
through the hlbes.
ram blowoutpreventern: ablowout preventer that uses rams to seal offpressure
on a hole that is with or without pipe. Also called a ram preventer. Compare
annular blowout preventer.
211
DIESEL ENGINES AND ELECTRIC POWER
raw water 17: in an engine's heat exchanger, water that circulates outside and
around the tubes through which the engine's coolant circulates. Raw water is
untreated water that removes heat from the engine's coolant. Offshore, raw water
is often seawater. Since raw water does not contact engine parts, it usua]]y does
reciprocating pump 11: a pump consisting of a piston that moves back and forth
or up and down in a cylinder. The cylinder is equipped with inlet (suction) and
outlet (discharge) vah·es. On the intake stroke, the suction valves are opened, and
fluid is dra\\11 into the cylinder. On the discharge stroke, the suction valves close,
the discharge valves open, and fluid is forced out of the cylinder.
relative density 71: 1. the ratio of the weight of a given volume of a substance at
the same temperature. For example, if I cubic inch ofwater at 39°F (3.9°C)weighs
I unit and I cubic inch of another solid or liquid at 39°F weighs 0.95 unit, then
the relative density of the substance is 0.95. In determining the relative density
ofgases, the comparison is made with the standard ofair or hydrogen. 2. the ratio
decreasing the positive voltage going to the electric actuator and governor. As the
engine needs more fuel to go faster, the reverse-acting actuator decreases the
positive voltage to make the governor increase the fuel. Compare direct-acting
nects agenerator from the system when an engine is underloaded and the generator
attached to it behaves like a motor. A generator acting like a motor draws current
from the system, instead of supplying current. The generator acting like a motor
then drives the underloaded engine, which can severely damage the engine.
rheostat n: a resistor that is used to vary the electrical current flow in a system.
rocker arm n: a bell-crank device that transmits the movement of the pushrod
roller bearing n: a bearing in which a finely machined shaft (the journal) rotates
in contact with a number of cylinders (rollers). Compare ball bearing.
Roots blowern: aspecial compressor used on two-stroke engines to supercharge
the engine's intake air and scavenge (remove) exhaust gases from the engine
cylinders. The blower has two corkscrew-shaped (helical) rotors with blades
(lobes) that rotate inside a housing. The engine drives the rotors with gears at
about twice the engine's speed. The rotors rotate in opposite directions at the
same speed. As they rotate, the lobes compress air drawn through an air cleaner
on top of the housing. The compressed air exits the blower from the bottom or
the side of tl1e housing and goes into the engine's air intake manifold.
212
GLOSSARY
rotor n: J. a de'ice with vanelike blades attached to a Sh<lft. The device turns or
rotates when the vanes are struck by a fluid directed there by a stator. 2. the
rotating pan of an induction-type alternating current electric motor.
Saybolt Second Universal (SSU) 12: a unit for measuring the viscosity oflighter S
shutdown n: the act ofstopping a machine or device from running. For example,
slip ring n: a conducting ring that gives current to or receives current from the
brushes in a generator or motor.
solenoid n: a cylindrical coil of wire that resembles a bar magnet when it carries
a current so that it draws a movable core into the coil when the current flows.
spark plugn: adevice that fits into the cylinder ofan internal-combustion engine
and that provides the spark for ignition of the fuel-air mixture during the
combustion stroke ofthe piston. It carries two electrodes separated by an air gap;
current from the ignition system discharges across the gap to form the spark.
speed droop n: the number ofrevolutions per minute that an engine slows down
21 3
speeder spring n: a small spring inside an engine governor that counteracts the
force of flyweights in the governor. The speeder spring moves down on a sleeve
in the governor to increase the fuel supply to the engine; at the same time, the
flyweights move the sleeve up to decrease the fuel supply. Since the flyweights
spin at a speed determined by the engine's speed, if engine speed drops, the
speeder spring moves down to speed the engine up. See flyweight, governor.
speed limiter n: a type of engine governor that prevents an engine from
exceeding a set speed. Usually, limiters simply prevent the engine from running
too fast to prevent damage to the engine; they do not shut down the engine.
spring-loaded centrifugal governor n: a mechanical governor that includes a
special spring, called a speeder spring, that offsets the centrifugal force of
spinning flyweights in the governor. In many governors, the flyweights tend to
make the governor slow the engine down, while the spring tends to make the
governor speed the engine up. Centrifugal force and spring pressure balance each
other to maintain the engine's speed.
spring shunt n: on a generator's brush holder, a braided copper wire conductor
that conducts (shunts) any current that may build up the brush holder's spring
away from the spring.
stack n: I. a vertical arrangement of blowout prevention equipment. Also called
preventer stack. See blowout preventer. 2. the vertical chimney-like installation
that is the waste disposal system for unwanted vapor such as flue gases or tail-gas
streams. See exhaust stack.
starter n: on an engine, an electrical, hydraulic, air, or other device used to rotate
the engine's flywheel or pistons so that the fuel, air, and (in some cases) spark can
enter the engine and make it begin running on its own.
statorn: 1. a device with vanelike blades that serves to direct a flow of fluid (such
as drilling mud) onto another set of blades (called the rotor). The stator does not
move; rather, it serves merely to guide the flow of fluid at a suitable angle to the
rotor blades. 2. the stationary part of an induction-type alternating-current
electric motor. Compare rotor.
storage battery n: a series of storage cells that produce electricity by chemical
action of acid or alkaline solution on metallic plates. Charging the battery with
DC electricity in the opposite direction restores the chemical condition neces
sary for further output of electricity.
strainern: 1. apartofa LACTunitthatremoves foreign particles from the crude,
which might disrupt the operation of close-tolerance moving parts. 2. a device'
placed upstream of a meter to remove foreign material from the stream that
might damage the meter or interfere with its operation. The strainer element is
generally coarser than a filter designed to remove solid contaminants.
stroke n: the up and down (reciprocating) movement of a piston in a cylinder.
strokes-per-cycle n pi: the number of strokes an engine piston makes inside a
cylinder to complete one firing cycle. Most engines are either two-strokes-per
cycle or four-strokes-per-cycle. In a two-strokes-per-cycle engine, the engine
crankshaft makes two revolutions to complete one cycle. As the crankshaft moves
GLOSSARY
the piston down on the first stroke, fuel is injected and combustion and power
occur. As the crankshaft moves the piston up on the second stroke, burned gases
go to exhaust, air is forced into the cylinder, and the piston compresses the air as
itmovesup the cylinder. In afour-strokes-per-cycle engine, the crankshaft makes
four revolutions to complete one cycle. As the crankshaft moves the piston down
on the first stroke, the piston draws in air (or it is forced in with a blower). As the
crankshaft moves the piston up, the piston compresses the air in the cylinder; just
before the piston reaches the top of its travel, fuel is injected. Combustion ofthe
fuel-air mixture creates power and moves the piston down. Finally, as the piston
moves up on the fourth stroke, the piston pushes the burned gases into the
exhaust system.
supercharge v: to supply a charge of air to the intake of an internal-combustion
engine at a pressure higher than that of the surrounding atmosphere.
supercharged engine n: an engine in which a compressor raises the pressure of
the air and forces it into the engine's cylinders.
supercharger n: a device that compresses atmospheric air and forces it into an
engine. Raising the pressure of an engine's intake air makes it denser and thus
delivers more oxygen into the cy!inder. More oxygen produces more power in the
combustion process.
synchronous speed n: in an electric motor, the speed of the rotating field:
. 120 X frequency (hertz)
synchronous speed (rpm) =
number of poles
synchroscope n: a device used by an engine operator to ensure that all the engines
on arig are running at synchronous speed. Ensuring synchronous speed is necessary
to avoid damaging a generator when taking it off line or putting it on line.
engIne.
tail pipe n: a pipe run in a well below a packer. 2. a pipe used to exhaust gases
I.
from the muffler of an engine to the outside atmosphere.
21 5
torque n: the turning force that is applied to a shaft or other rotary mechanism
to cause it to rotate or tend to do so. Torque is measured in foot -pounds, joules,
newton-metres, and so forth.
total volume n: in diesel engine fuel tanks, the full capacity of the tank; usually,
not all the fuel in the tank is usable. Compare useful volume.
turbine n: a bladed rotor flowmeter component that turns at a speed that is
proportional to the mean yelocity of the stream and therefore to the volume rate
of flow.
turbocharger 71: a centrifugal blower driven by exhaust gas turbines and used to
supercharge an engine.
two-stroke diesel engine 71: an engine in which the piston moves from top dead
center to bottom dead center and then back to top dead center to complete a
cycle. Thus, the crankshaft must turn one revolution, or 360°.
V vacuum n: I. a space that is theoretically devoid ofall matter and that exerts zero
pressure. 2. a condition that exists in a system when pressure is reduced below
atmospheric pressure.
valve overlap n: the phenomenon that occurs during the operating cycle of an
engine in which both the intake and exhaust valves are open at the same time.
Valve overlap occurs in a four-strokes-per-cycle engine at the end of the engine's
exhaust stroke and the beginning of the intake stroke. Both valves being open
allow exhaust gases to finish leaving the cylinder and, at the same time, allow inlet
air to begin filling the cylinder. Valve overlap ensures that the cylinder is
completely filled with fresh air; also, the cool incoming air helps cool the hot
exhaust valve.
viscosity n: a measure of the resistance of a fluid to flow. Resistance is brought
about by the internal friction resulting from the combined effects ofcohesion and
adhesion. The viscosity of petroleum products is commonly expressed in terms
ofthe time required for a specific volume of the liquid to flow through a capillary
tube of a specific size at a given temperature.
volatility n: the tendency of a liquid to assume the gaseous state.
voltage n: potential difference or electromotive force, measured in volts.
voltmeter n: an instrument used to measure, in volts, the difference of potential
in an electrical circuit.
216
GLOSSARY
water jacket n: in the cooling system, a passageway inside the rim for circulating W
water.
water pump n: on an engine, a device, powered by the engine, that moves coolant
(water) through openings in the engine crankcase, through the radiator or heat
exchanger, and back into the crankcase.
weight on bit (WOB) 71: the amount of downward force placed on the bit by the
weight of the drill collars.
wet air cleaner n: see oil-bath air deaner.
wonn gear n: the gear of a worm (a short revolving screw with spiral-shaped
threads) and a worm wheel (a toothed wheel gearing with the thread of a worm)
working together.
wrist pin n: in an engine, the hard steel, hollow cylinder that attaches the piston
to the piston rod. Acircular opening in the piston is lined up with acorresponding
circular opening in the rod and the wrist pin is pushed through the openings.
Usually, special keys on each end of the pin lock the pin in the piston. Also called
piston pin.
21 7
Review Questions
Multiple Choice
Pick the best answer from the choices and place the letter of that answer in the blank provided.
I. Diesel engines are often used to power drilling rigs because
a. a diesel engine creates more torque than a gas or an LPG engine.
b. diesel fuel is more portable than natural gas.
c. diesel fuel does not vaporize as easily as LPG.
d. all of the above
2. To nm correctly, a spark ignition (5I) engine requires a fuel-air ratio of
about
a. IOto I.
b. 15 to I.
c. 20 to I.
d. is not critical
3. To run correctly, a compression ignition (CI) engine requires a fuel-air
ratio of about
a. 10 to I.
b. 15 to I.
C. 20 to I.
d. is not critical
21.
Identify
Identify the numbered parts on the drawings.
II.
12.
16.
220
REVIEW QUESTIONS
26.
17·
18.
20.
21.
22.
23·
26.
28.
30.
31.
32 .
221
DIESEL ENGINES AND ELECTRIC POWER
temperature at which a fuel, when heated, gives off enough flammable vapors to momen
ability to ignite.
True or False
Put a T for true or an F for false in the blank next to each statement.
42. In a diesel engine installation, ifthe main supply tank is placed at the same
height as the day tank, a pump' to transfer fuel from the day tank to the
main tank is not required.
43. To purge air from the fuel system, it is necessary to circulate more fuel
through injectors than they need to spray into the engine.
44. Vents on fuel tanks are desirable but not necessarily required.
45. Adding water to fuel to clean it is not an acceptable procedure unless the
fuel and water are centrifuged.
222
REVIEW QUESTIONS
46. Keeping rotary-type fuel transfer pumps at the same level as the main fuel
tanks is not necessary because rotary pumps can raise fuel to any required
level.
48. Most diesel fuel systems do not require return lines from the injectors
back to the fuel tanks.
49. When starting an engine itis not necessary to bleed air from the fuel lines.
Matching
Write the letter of the correct definition in the blank next to the term.
Terms
Definitions
223
DIESEL ENGINES AND ELECTRIC POWER
Multiple Choice
Pick the best answer from the choices and place the letter of that answer in the blank provided.
57. Governors operate on the principle of
a. gravity.
b. electricity.
e. centrifugal force.
d. engine speed.
58. Speed droop is
a. a variation in engine speed from too fast to too slow.
b. a decrease in engine speed from a no-load to a full-load condition.
e. the amount of speed change an engine makes before the governor
corrects it.
d. the time a governor takes to react to a change in engine speed.
59. Hunting is
a. a variation in engine speed from too fast to too slow.
b. a decrease in engine speed from a no-load to a full-load condition.
c. the amount of speed change an engine makes before the governor
corrects it.
d. the time a governor takes to react to a change in engine speed.
60. An isochronous governor
a. stops the engine immediately if the engine overspeeds.
b. speeds up the engine when the load decreases.
c. makes the engine idle smoothly.
d. maintains the engine's speed regardless of the engine's load.
6 I. Three main types of governors are
a. mechanical, gravity driven, and electrical.
b. mechanical, hydraulic, and electrically actuated.
c. gravity driven, pneumatic, and electrical.
d. pneumatic, hydraulic, and mechanical.
True or False
Put a T for true or an F for false in the blank next to each statement.
62. When an engine is running, only about 20 percent of its oil forms a
lubricating film.
63. It is okay to use a spin-on fuel filter as an oil filter.
64. Ifthe pressure on two gauges mounted on each side ofthe oil filter differs by
about 30 psi (200 kPa), the filter is doing its job and should not be changed.
224
REVIEW QUESTIONS
Matching
Write the letter of the correct definition in the blank next to the term.
Terms
76. naturally aspirated
77· supercharged
80. turbocharger
Definitions
a. An air cleaner that uses filters and screens that do not require a liquid to work properly.
b. Adevice, usually driven by an engine's exhaust, that consists ofacompressor and a turbine,
which compress air for the engine to use in combustion.
c. Descriptive of an engine that takes in air at atmospheric pressure.
d. An air cleaner that uses oil, in addition to filters and screens, to filter air enteling the engine.
e. Adevice, usually driven by gears on the engine, that raises the pressure ofthe air going into
the engine.
225
DIESEL ENGINES AND ELECTRJC POWER
Identify
On the drawing below, identify the numbered parts.
82.
pyrometer electric
tachometer operating
water manifold pressure gauge
hydraulic (or air) pressure
temperature point (or place)
Two reasons a diesel may not start are that the 85. and
be used on small diesels, but large diesels often use 88. starters.
pressure on the lube oil system at the 90. where the gauge
to condense inside the engine. Coolant temperature gauges indicate the 92. _
93· - - - - - - - - - - - - - _ . A 9+ measures
226
REVIEW QUESTIONS
True or False
Put a T for true or an F for false in the blank next to each statement.
95. Alamls and shutdown systems on engines are mainly used to alert the
toolpusher that the driller and rig mechanic are not properly maintaining
the engines.
96. Overspeed trip devices can shut down an engine either by shutting off fuel
or by shutting off fuel and air going to the engine.
97. A low oil-pressure alarm merely indicates that it is time to add oil to the
engIne.
Multiple Choice
Pick the best answer from the choices and place the letter of that answer in the blank provided.
102. An exciter is a
a. small AC generator.
b. small DC generator.
c. big magnet.
d. device that starts up an AC generator.
227
DIESEL ENGINES AND ELEcrRlC POWER
228
Anwsers to Review Questions
valve 49- F
17·
18.
50. T
push rod
24· piston
55. b
26. exhaust
73·
T
True or False
74· F
75· F 95· F
96. T
Matching
97· F
76. c 98. F
77· e 99· T
78. a
100. T
79· d
80. b
Multiple Choice
Identify 10J. d (a and c)
8J. exhaust manifold 102. b
82. exhaust pipe 10 3. d
- 83· muffler 1°4· d
84· tail pipe l°S· a
23°
Austin, TX 78712-1100
or (800) 687-4132
or (800) 687-7839
ISBN 0-88698-169-7
9 780886 981693
2.108301
0-88698-169-7