COMBUSTION

REACTIONS

1
Combustion is the conversion of a substance
called a fuel into chemical compounds known
as products of combustion by combination
with an oxidizer.
Combustion process is an exothermic
chemical reaction, i.e., a reaction that releases
energy as it occurs.

Fuel + Oxidizer = Products of combustion + Energy

2
3
 Theoretical Air, Excess Air
Air contains approximately 21% oxygen (O 2) by
volume. The other 79% of "other gases" is mostly
nitrogen (N2), so we will assume air to be
composed of 21% oxygen and 79% nitrogen by
volume.
Thus each mole of oxygen needed to oxidize the
hydrocarbon is accompanied by 79/21 = 3.76
moles of nitrogen.

4
 Thus, for complete combustion of carbon and hydrogen,

In OXYGEN In AIR

The amount of air required in the equations above

is called the stoichiometric air or the theoretical
air or chemically correct air.
It is the minimum amount of dry air that would
supply sufficient oxygen for complete combustion of
the fuel.
5
• Excess air is air that is supplied for combustion in
excess of theoretical air requirements.
• It is expressed as a percentage of the theoretical
air. Thus ‘120 percent theoretical air’ is equivalent
to 20 percent excess air.
• An insufficient amount of excess air will lead to
incomplete combustion, resulting in CO or an
unburned fuel (HC).

6
 Combustion Stoichiometry

 Combustion in Oxygen

Cn H m  O2  CO2  H 2O

1. Can you balance the above equation?

2. Write the reactions for combustion of methane and
benzene in oxygen, respectively.
Answer

 m m
C n H m   n  O2  nCO2  H 2O
 4 2

CH 4  2O2  CO2  2 H 2O

C6 H 6  7.5O2  6CO2  3H 2O

7
 Combustion Stoichiometry

 Combustion in Air (O2 = 21%, N2 = 79%)

Cn H m  (O2  3.76 N 2 )  CO2  H 2O  N 2

1. Can you balance the above equation?
2. Write the reactions for combustion of methane
and benzene in air, respectively.
Answer

 m m  m
Cn H m   n  (O2  3.76 N 2 )  nCO2  H 2O  3.76 n   N 2
 4 2  4

CH 4  2(O2  3.76 N 2 )  CO2  2 H 2O  7.52 N 2

C6 H 6  7.5(O2  3.76 N 2 )  6CO2  3H 2O  28.2 N 2

8
9
 Air-Fuel Ratio
 Air-Fuel (AF) ratio
AF = m Air / m Fuel
Where: m air = mass of air in the feed mixture
m fuel = mass of fuel in the feed mixture
Fuel-Air ratio: FA = m Fuel /m Air = 1/AF

 Air-Fuel molal ratio

AFmole = nAir / nFuel
Where: nair = moles of air in the feed mixture
nfuel = moles of fuel in the feed mixture
What is the Air-Fuel ratio for stoichiometric combustion
of methane and benzene, respectively?
10
 Air-Fuel Ratio
 Rich mixture
- more fuel than necessary
(AF) mixture < (AF)stoich

 Lean mixture
- more air than necessary
(AF) mixture > (AF)stoich

Most combustion systems operate under lean conditions. Why is

this advantageous?

11
• If octane (C8H18) is burned with 100 percent theoretical air, the
complete combustion equation is a follows:

12
Class work
• Do same for C6H14 and C12H26 combustion with 100%,
130% and 80% (assuming complete combustion of
hydrogen) theoretical air. Find the A/F ratio and
equivalence ratio (Ø) in each case.

13
 Equivalence Ratio (Ø)

Equivalence ratio: shows the deviation of an actual

mixture from stoichiometric conditions.
( FA ) actual ( AF ) stoich
 
( FA ) stoich ( AF ) actual

The combustion of octane has an equivalence ratio

Φ=0.8 in a certain condition. What is the percent of
excess air (EA) used in the combustion?
14
15
Example 1.

16
17
2. Ethane (C2H6) is burned with atmospheric air, and the volumetric analysis
of the dry products of combustion yields the following: 10% CO 2, 1% CO,
3% O2, and 86% N2. Develop the combustion equation, and determine a)
the percentage of excess air, b) the air-fuel ratio.

18
19
 What is the equivalence ratio?
?
20
 ENTHALPY OF REACTION,  Hrxn
• Consider a combustion reaction at a constant
pressure with no work transfer, in a steady
state steady flow device:

• Applying first law of thermodynamics

neglecting the changes in kinetic and potential
energies, we have:
21
Where HP = Enthalpy of products at section 2 and
HR = Enthalpy of reactants at section 1

22
• This property is the enthalpy of reaction which
is defined as the difference between the enthalpy
of the products at a standard state and the
enthalpy of the reactants at the same state for a
complete reaction.
• For combustion processes, the enthalpy of
reaction is usually referred to as the enthalpy of
combustion , which represents the amount of
heat released during a steady-flow combustion
process when 1 kmol (or 1 kg) of fuel is burned
completely at a standard temperature and
pressure
23
• For example, Consider the formation of CO2 from its
elements, carbon and oxygen, during a steady-flow
combustion process. Both the carbon and the oxygen enter
the combustion chamber at 25°C and 1 atm.
• The CO2 formed during this process also leaves the
combustion chamber at 25°C and 1 atm. The combustion
of carbon is an exothermic reaction (a reaction during
which chemical energy is released in the form of heat).
Therefore, some heat is transferred from the combustion
chamber to the surroundings during this process, which is
393,520 kJ/kmol CO2 formed.

24
• If the reactants and products are both at the same
temperature, the quantity ∆H is called the
enthalpy of reaction. It is also called the heat of
reaction or enthalpy of combustion or heating
value of fuels.
• If Q is positive, heat is added to the system and
HP> HR, the reaction is endothermic. If Q is
negative, heat is released by the system, the
reaction is exothermic and HP < HR.

25
The heating value of fuels is expressed in kJ/kg fuel.
The H2O in the products may appear in either the liquid or vapor
phase.
When the H2O appears in the liquid phase, the heating value is
called the higher heating value of the fuel.

When the H2O appears in the gas phase, the heating value is
called the lower heating value of the fuel.

The difference between the higher heating value (HHV) and the
lower heating value (LHV) is simply the energy associated with
the vaporization of water formed in the burning of fuel.

26
In almost all practical cases, the water in the products
is vapor; the lower value is the one which usually
applies.

27
 Heat/Enthalpy of formation

• Is the heat of reaction for the formation

of one mole of a compound from its
elements in their most stable form at
standard conditions of 1atm and 25oC.

28
• Examples
1. H2 (g) + ½ O2 (g) = 1H2O
• The heat of formation of most elements @their
stable form is Zero.
•  Horxn = nPHfo p - nR Hfo R

29
1. Which of the following represents a standard heat (enthalpy) of
formation:
• CO(g) + ½ O2(g) 2H2O(g )
• 2H2 (g)+O2 (g) 2H2O()
• 2 Na (s) +O2 (g) Na2O(s)
• 2K ()+CO2 (g) 2kcl (s)
• C (graphite) +O2 (g) CO2 (g)

30
3. Consider the decomposition of 1 mole of solid calcium
carbonate. The standard heat of rxn,  Horx,is
178Kg.Calculate Hof for CaCO3.
• CaCO3(s) CaO(s) +CO2 (g)
 Horxn= HofCaO (S) +HofCO2 (g) - HofCaCO3 (s)
  178kg/mol = - 635.5 kg/mol + -395.5 kg/mol - HofCaCO3
  HofCacO3= -1207 kg/mol , CaCO3

31
4. Consider 4C3H5N3O9 (l) 6N2 (g) +12C02 (g) +10H2O (l) +O2 (g)
• Given  Horxn= - 6165.6 kg
  Horxn = 6HOfN2+ 12 Hofco2 + 10 HofH2O + HOfO2 - 4
HOfC3H5N3O9
  - 6165.6 Kg = 6(0) +12(-393.5 kg/mol )+10 ( -285.8 kg/mol ) +1(0) -4
HOfc3 H5 N3O 9
  HOfc3H5N3O9 () = -354 kg

32
5. Consider the complete combustion of 1 mol of propane gas- forming
gaseous CO2 and water what is the standard heat of rxn , HOrxn for
this reaction?
• Eqn; C3H8 (g)+5O2 (g) 3CO2 (g)+ 4 H2O(l)
 HOrxn = (3Hof CO2 +4Hof H2O ) - ( Hof Propane +5 HOfO2)

• = [3(-393.5) kg/mol +4 (-285.8 kg/mol )] – (-103.85 kg/mol + 5 X 0)

• = -2219.85 kg/mol or rxn = -2219.85 kg/mol of prop
• How much heat is generated by combustion of 98.5 grams of propane?
• 1mol C3H8= (3*12+8*1) grams.
• X mol = 98.5 grams
• X= 1molx98.5 grams = 2.23 mols of propane
(3x12+8)grams
• Heat generated from combustion of 98.5 gram of propane
= 2.23 * -2219.85 = 4950.4 kJ
33
6. Consider complete combustion of 1mol of liquid benzene (C6 H6)
with oxygen forming gaseous CO2 and water .What is  HO rxn
for this rxn.
• How much heat is generated by combustion of 257.5 grams of
benzene.
• C6 H6 (l) + 7.5 O2(g) 6 CO2(g) + 3H2O(l)
• HO rxn= -3267.4 kg/(mol of C6H6)
 
• 1mol C6H6 = (6*12+6) grams
? = 257.5 grams
•  
• Mols of C6H6 = 257.5x1mol = 3.296mols
(6x12+6)
  HO rxn for 257.5 grams of Benzene
• = 3.296 * -3267.4 = -10769.35 Kg of heat
34
ADIABATIC FLAME TEMPERATURE (AFT)
• Adiabatic means without losing heat.
• Thus, adiabatic flame temperatures would be
achieved in a (theoretical) combustion system
in which there are no heat losses and, hence,
no radiation losses from the flame.
• Because this cannot be achieved in practice
(due to the inefficiencies of combustion) and
is never achieved in a fire situation, adiabatic
flame temperatures are calculated values.

35
• The amount of energy or heat released from the
combustion reaction of fuel and air (or oxygen) is
the heat of combustion.
• If all of the energy released by this chemical
reaction were used to raise the temperature of the
products (CO2, H2O, and N2) with no heat losses,
the resultant temperature would be the adiabatic
flame temperature, which represents the
maximum possible theoretical temperature for
particular fuel/oxidant combustion.

36
37
 Importance of knowing AFT

• Know Characteristic of quality of fuel

• Determine the quality of fuel for a specific
application
• Determine the extent of substitution of a
lower quality fuel

38
 COMBUSTION IN S.I. ENGINES

The main conditions for combustion of fuel in S.I.

engines are
1. Presence of a combustible mixture of fuel and
air, supplied by fuel injectors or carburetor.
2. Some means of initiating combustion by a spark
plug.
3. Stabilization and propagation of flame in the
combustion chamber.

39
Combustion in four stroke spark ignition engines is a
complex cyclic process consisting of air intake, fuel
injection, compression, spark ignition, combustion,
expansion, and finally gas exhaust phases.

40
 COMBUSTION STAGES

The combustion process can be divided into:

1. Flame development, and
2. Flame propagation.

Point A: spark at the end of

compression stroke
A-B: Ignition Lag =Time interval
between spark and attainment of
self- ignition temperature by the
mixture.

B-C : Flame Propagation :

Propagation of flame through the
mixture.

If fuel continues to burn after peak cylinder pressure at C is

reached, it is called after burning. 41
 EFFECT OF ENGINE VARIABLES ON IGNITION LAG

1. Fuel type. Higher the self ignition temperature of the fuel used,
the longer the ignition lag.
2. Mixture Ratio. The mixture ratio somewhat richer than
stoichiometric ratio gives minimum ignition lag.
3. Initial Temperature and Pressure. Ignition lag decreases with
increase in temperature and pressure at the time of spark.
4. Electrode Gap. Electrode gap should be adjusted for the
compression ratio and mixture strength. If the gap is too small,
quenching of flame nucleus may occur.
5. Turbulence. Excessive turbulence of the mixture in the area of
spark plug is harmful, since it increases the heat transfer from the
combustion zone and leads to unstable nucleus of flame.

42
 EFFECT OF ENGINE VARIABLES ON FLAME
PROPAGATION
1. Fuel-Air Ratio. The maximum flame speed occurs
when the mixture is about 10% richer than
stoichiometric as it produces maximum
temperature.
2. Compression Ratio (engine parameter). An increase
in compression ratio increases the flame speed
because of higher density and temperature of the gas.
3. Intake Temperature. Increase in intake temperature
increases flame speed.
4. Intake Pressure. The higher the intake pressure, the
higher the flame speed due to higher density.
43
5. Turbulence. The flame speed is very low in non-
turbulent mixtures. Flame speed increases with
turbulence due to internal friction of heat transfer
process and mixing of burned and unburned portion
of flame front.
6. Engine Speed. The higher the engine speed, greater
the turbulence and higher the flame speed. Flame
speed linearly increases with engine speed.
7. Engine Size. Speed of flame propagation is reduced
with engine size as it has to travel longer distances
in big engines.
44
 ABNORMAL COMBUSTION
 
• Under certain operating conditions, abnormal
combustion may take place affecting the life and
performance of the engine. The various abnormalities of
combustion process are listed below.
1. Pre-ignition. There can be ignition of charge by the
presence of some hot surface within the engine such as
red hot carbon deposits and overheated spark plug
before actual ignition by the spark. There is a serious
loss of combustion efficiency and engine output due to
pre-ignition phenomenon.

45
2. After burning. Burning may continue even after
fuel injection is over. It results in reduction of
power output.
3. Detonation or Knock. Some shock wave or
some other disturbance within the combustion
chamber establishes a wave which propagates
through the unburned charge at a supersonic
speed. This causes a sharp pressure discontinuity
resulting in gas vibrations and a sharp metallic
sound called a ping/knock.

46
 THE PHENOMENON OF DETONATION OR
KNOCKING

1. Normal combustion. Normal flame front travels across

the combustion chamber from A towards B with a
speed of 15 to 30 m/s. As the flame front advances, it
compresses the unburned charge, raising its
temperature. If the temperature is less than auto-
ignition, normal combustion takes place and flame front
will reach the farthest point of the chamber, D.

47
2. Detonation. If the end charge (CDC) in Figure (b)
below, auto-ignites before the flame front reaches it by
acquiring auto-ignition temperature due to favorable
conditions of pressure and density of the unburned
charge, there will be detonation.

48
 EFFECTS OF DETONATION

1. Noise and Roughness

2. Pre-ignition
3. Mechanical Damage
4. Increase in Heat Transfer
5. Decrease in Power Output and Efficiency.
6. Carbon Deposits

49
 Sources of pre-ignition
1. Carbon deposits
2. The electrodes of the improperly selected spark plugs
may operate too hot. It can lead to pre-ignition.
3. Overheated spark plugs.
4. Hot exhaust valves
5. Highly supercharged engines reject more heat to
combustion chamber walls which act as source of heat.

50
 COMBUSTION IN C.I. ENGINES

• Compressions ignition engines or diesel engines

are thermodynamically similar to spark-ignition
engines. The cycles for both include suction,
compression, addition of heat, expansion and
exhaust.
• But the combustion process and method of
control in C.I. engines are very different from
those in S.I. engines.
51
 STAGES OF COMBUSTION
• For convenience in analysis, the combustion process in C.I
engines is usually divided into four stages:
1. The delay period,
2. Rapid combustion period,
3. Period of controlled combustion.
4. After burn

52
1. The delay period (Ignition delay) (A-B)
• This is the phase preparatory to combustion in which the fine particles
of the injected fuel evaporate and mix with the air in the cylinder to
form an ignitable mixture, also called delay time or Ignition delay.
2. Rapid combustion period (Flame propagation) (B-C)
• By the end of the first stage, a combustible mixture has formed in
various parts of the cylinder, with ignition starting in several places.
These flames propagate at extremely high speed so that the mixture
burns almost explosively, and causes the pressure within the cylinder
to rise rapidly. Thus, this is sometimes called the explosive
combustion stage.
The pressure rise in this stage is proportional to the amount of
combustible mixture formed in the first stage (ignition delay).

53
 3. Period of Controlled Combustion (Direct combustion) (CD)
• At the end of the period of rapid combustion, the temperatures
within the cylinder are so high that any fuel injected after this time
will burn as soon as it finds oxygen. Direct combustion of the fuel
still being injected takes place during this stage due to immediate
fuel ignition by the flame in the cylinder. The combustion can be
controlled by the amount of fuel injected in this stage, so this is also
described as the controlled combustion period.
4. After burning (From D- onwards)
• The injection ends at point D, but the fuel not yet in the combusted
state continues to burn. If this stage is too long, the exhaust gas
temperature will rise, causing a drop in efficiency.

54
 DIESEL KNOCK

• If the rate of the pressure rise (dp/dt) during second

stage of uncontrolled combustion is very high, it may
give rise to a violent pounding noise. This noise is
called diesel knock. Since combustion knock in a C.I.
engine can have the same damaging effects as that of
detonation in S.I. engines, it is important to eliminate
knocking altogether.
 

55
• The factors controlling the diesel knock are just
reverse of those required to suppress knock in
S.I. engines.
• For example, increase in intake temperature,
intake pressure, compression ratio, jacket
temperature, engine speed, and turbulence and
decrease in self-ignition temperature of fuel
tend to suppress diesel knock but these promote
detonation in S.I. engines.

56
The following methods are employed to reduce diesel
knock:
1. Using fuel with a high cetane value,
2. Raising the air temperature and pressure at the start of
injection,
3. Reducing the injection volume at the start of fuel
injection,
4. Raising the combustion chamber temperature (especially
in the immediate area of fuel injection)

57
 READING ASSIGNMENT

• WHAT ARE THE DIFFERETNT TYPES

OF COMBUSTION CHAMBER DESIGNS
IN S.I. AND C.I. ENGINES.

58
THANK
YOU
59
60
61
 Fuel System Types
• Direct Injection (DI)
– Fuel injected directly in combustion chamber

– Mixing achieved by using a multi-hole nozzle and or by

causing the intake air to swirl

– High injection pressures (2,000-30,000 psi) required for fine

atomization

– Generally uses less fuel than Pre Combustion chamber engine

– More sensitive to fuel quality
62
Direct Injection

63
 Fuel System Types

• Precombustion Chamber (PC)

– Fuel injected into a precombustion chamber
– Mixing is achieved by spraying fuel into the
turbulent air (generally a single-hole nozzle)
– Low injection pressures (1,500-5,000 psi)
– Less sensitive to the degree of fuel atomization
– Less sensitive to fuel quality
– Lower fuel economy
64
Precombustion Chamber

65
 Diesel Fuel Grades

• Minimum quality standards for diesel fuel

grades have been set.

66
 Classification No. 1-D

• Volatile fuels from kerosene to the

intermediate distillates

• Use in high-speed engines involving frequent

and wide variations in speeds and loads

• For use in low ambient temperatures

• Has highest volatility
• Lowest pour and cloud point 67
 Classification No. 2-D

• Higher volatility, pour point, and cloud point than

grade 1
• Most commonly used diesel fuel grade
• In cold climates, diesel 1 and 2 mixed to provide
easier starting
• Fuel mileage drops due to the addition of diesel 1

68
 Classification No. 4-D

• The more viscous distillates and blends of distillates with

residual fuel oils

• For use in low- and medium-speed services involving

sustained loads and constant speeds

• Used by large stationary power generation and marine

engines

69
 Typical Diesel Fuel Properties
No. 1-D No. 2-D No. 4-D
Gravity API 39-45 31-37 14-23
Flash Point °F 102-130 150-240 155-260
Viscosity (cSt) 1.3-1.7 2.8-4.1 5.5-24.0
Sulfur % 0.05-0.5 0.03-0.45 0.24-1.5
Cetane No. 45-48 45-48 32-36
BTU/lb 19,700 19,500 18,800
BTU/gal 134,000 138,000 148,000

70
 Properties

• Cetane Number
– Ignition quality measure - affects cold starting,
smoke, and combustion
• Sulfur Content
– Affects wear, deposits, and particulate
emissions
• API Gravity
– Related to heat content, affecting power and
economy
71
 Properties

• Heating Value
– Affects power output and fuel economy

• Volatility
– Affects ease of starting and smoke

• Flash Point
– Related to volatility and fire hazard in handling
72
 Properties

• Viscosity
– Affects injector lubrication and atomization
• Cloud Point
– Affects low-temperature operation
• Water & Sediment
– Affects life of fuel filters, pump, and injectors

73
 Properties
• Carbon Residue
– Measures residue in fuel, can influence
combustion
• Ash
– Measures deposit-forming inorganic residues
• Corrosion
– Measures possible corrosive attack on metal
parts
74
 Cetane number
• The cetane rating of a diesel fuel is a measure of its
ability to auto ignite quickly when it is injected into the
compressed and heated air in the engine.
• Though ignition delay is affected by several engine
design parameters such as compression ratio, injection
rate, injection time, inlet air temperature etc., it is also
dependent on hydrocarbon composition of the fuel and
to some extent on its volatility characteristic.
• The cetane number is a numerical measure of the
influence the diesel fuel has in determining the ignition
delay
75
 Cetane Number
• Ignition quality measure
• Affects: cold starting, warm-up, combustion roughness,
acceleration, and exhaust smoke density

• Cetane number is based on the ignition characteristics of two

hydrocarbons:
• Cetane - short delay period and ignites readily (100)
• Alphamethylnaphthalene (AMN) - long delay period and poor
ignition quality (0)

• It is the percentage by volume of normal cetane in a blend with

AMN
76
 Cetane Number

• High cetane number indicates good ignition quality (short

delay period)

• Low cetane number indicates poor ignition quality (long

delay period)

• PC engines require a minimum cetane # of 35

• DI engines require a minimum cetane # of 40
• Cetane improver additive can improve ignition quality
and reduce white smoke during start up
77
78
79
 Sulfur Content
• Limited to .05% sulfur by law.
• cause wear, deposits, and particulate emissions

• Depends on the crude oil source and refining steps it

undergoes

• Sulfur oxides (SO2 and SO3) are produced during

combustion of fuel. SO3 combines with water in the exhaust
to form sulfuric acid (H2SO4)

• Sulfuric acid causes corrosive wear and contributes to

engine deposits
80
Sulfur Damage

81
 API Gravity
• The American Petroleum Institute gravity, or
API gravity, is a measure of how heavy or
light petroleum liquid is compared to water. If
its API gravity is greater than 10, it is lighter
and floats on water; if less than 10, it is
heavier and sinks.
• API gravity is thus an inverse measure of the
relative density of a petroleum liquid and the
density of water, but it is used to compare the
relative densities of petroleum liquids.
82
•Related to heat content, affects power and
economy

•It is an arbitrary index of the weight of a

measured volume of fuel and is related to
specific gravity and density

•The scale is inverse to specific gravity

•Lighter fuels have higher API numbers 83
 API Gravity

• For most Cat engines an API reading of 35 is optimum

• Lighter fuels, like kerosene, read about 44 API

• Heavier fuels (below 30 API) create combustion

chamber deposits which cause abnormal wear

• Blending is the only way to correct fuel density

problems
84
 Heating Value

• Affects power output and fuel economy

• The heat of combustion (BTU per pound or

gallon) is a measure of the amount of energy
available to produce work

• In general, a fuel with a higher volumetric

heating value (BTU per gallon) will produce
more power or provide better fuel economy
85
 Fuel Volatility
• Affects ease of starting and smoke.

• Less volatile fuels (higher boiling points) normally have a

higher heating value.

• Starting and warm-up are better with higher front-end

volatility.

86
 Flash Point

• Related to volatility and fire hazard in handling

• It is the temperature at which fuel vapors can be ignited when

exposed to a flame

• Affected by the type of fuel and the air/fuel ratio

• It is important for safety reasons, not for engine operating

characteristics

• The minimum flash point for most diesel fuels is about 100°F (38°C)
87
 Viscosity

• Affects injector lubrication and atomization

• Low viscosity fuels may not provide sufficient lubrication in

close-fit pumps and injectors

• Can cause abnormal wear, loss of power & smoke

• Influences the size of the fuel droplets

• High viscosity increases wear of fuel pump and injection pump

due to high injection pressures
88
Effect of Viscosity

89
 Cloud Point
• Affects low-temperature operation

• Cloud Point is the temperature where a cloud or haze appears in the

fuel

• Happens when the temperature falls below the melting point of the
wax in the fuel

• CP must be below the lowest outside operating temperature to prevent

filter plugging

• Use a fuel heater or blended fuel, additives are not recommended

90
 Water & Sediment

• Affects life of fuel filters, pump, and injectors

• Water introduced during shipment or as condensation

during storage Cause damage, especially to fuel
lubricated pumps
• Water separators are critical to fuel systems
• Sediment (rust, scale, dirt, weld slag, etc.)

• Removed by settling, straining/filtration, or centrifuging

91
Sediment

92
 Water & Sediment

• Eliminate water by draining the fuel tank regularly

• Obtain fuel from reliable sources
• Water separators should be used
• Sediment should not exceed 0.05% to the engine
• Primary and secondary filtering is usually required

93
Nozzle Orifice Wear

94
 Carbon Residue
• Measures residue in fuel, can influence combustion

• Carbon rich fuels are harder to burn

• Leads to the formation of soot and carbon deposits

• Hot spots on liners, burned oil film, scuffing, stuck

rings, turbocharger and engine deposits are the
results

95
Carbon Residue

96
 Ash
• Deposit-forming inorganic residues

• Consists of metal and other contaminants that cannot be burned

• Cause localized overheating of metal surfaces such as the exhaust

valve seat

• Causes wear of cylinder and fuel system components, and the

turbocharger

• Avoid use of unproven additives, use filters and settling tanks to

remove solids

97
Ash Deposits

98
 Hydrogen Sulfide

• H2S is a poisonous gas present in some crude oils and

residual fuels

• Forms sulfuric acid when combined with water vapor in

the cylinder

• Corrosive to metals, particularly valve guides, rings, and

liners

• If above 0.05% coolant temp must be kept above 190°F

to prevent condensation
99
 Copper Strip Corrosion

• ASTM Test D130, a polished copper strip is

immersed in fuel for three hours at 212°F

• Any fuel showing more than a slight

discoloration should be rejected

• Certain sulfur derivatives in the fuel are the

likely sources of corrosion
100
101
 Microbial Contamination

• Fuels are sterilized during refining

• Contamination occurs after leaving the refining

• Bacteria and fungi exist harmlessly in moisture and

fuel and pass through the fuel system without causing
harm.

• When water is present they multiply and grow

102
 Microbial Contamination
• Plug filters with a greenish-black or brown cream
• Frequently strong odor
• Some produce corrosive acid byproducts
• Prevent growth by keeping fuel system dry
• Treat with biocides when a reoccurring is problem
• Tanks and lines must be cleaned to reduce filter
plugging

103
 Stability
• Sulfur and Nitrogen present in diesel fuel make it more
prone to oxidative attack in storage, and thermal
degradation in use, than gasoline

• Gums and Resins are the result of oxidation and cause

rapid filter plugging

• Commercial fuels usually contain additives to help

prevent oxidative breakdown

• Storage time should be less than one year

104
 Smoke and Particulates

• White/Blue Smoke
– Usually the result of too low a temperature in
the combustion chamber
– Blue component is excess lubricating oil in the
combustion chamber

• Black Smoke
– Produced at or near full load
– Excess fuel or not enough air

105
 Diesel Additives
• Contaminant Control
– Biocides - prevent bacterial growth
– Demulsifiers - separate water from fuel
– Corrosion Inhibitor- protect against rust and corrosion
• Fuel Stability
– Oxidation Inhibitors - protect against breakdown
– Metal Deactivators – deactivate traces of metals
– Dispersants - disperse residues and prevent agglomerations

106
 Diesel Additives
• Engine Performance
– Detergents - prevent deposit buildup and extend
injector life. Increase filter life by keeping the filters
clean
– Cetane Improvers - raise cetane number
– Lubricity - replaces natural lubricants
• Fuel Handling
– Anti-foam - reduces foaming when pumping fuel
– Anti-Static - lowers risk of static induced explosion
107
 Fuel System Maintenance
• Clean around filter housing before removing filter

• Lubricate and clean the new filter gasket with clean fuel

• Always bleed the fuel system to remove air after

changing the filter

• Fill the fuel tank at the end of the day to prevent

condensation of water
108
 Fuel System Maintenance
• Drain Water and sediment from the fuel tank at the start of
each day or after the tanks has been filled and allowed to
stand for 10-15 minutes

• Install and maintain a water separator before the primary fuel

filter

• Clean and change filter at the recommended interval

• Inspect new filters for debris or metal filings, especially the

threads of spin-on filters
109
 Fuel System Maintenance
• Drain storage tanks every week

• Use genuine fuel filters. There are great differences in

fuel filters

• Properly store new filters to prevent dust and dirt entry

• Cut apart used filters to examine contaminants and

compare brands of filters

110
Fuel Quality is Not Visually Apparent

111