I C ENGINES

P R Venkatesh, Mech Dept, RVCE, B'lore

 INTERNAL COMBUSTION ENGINES
Any type of engine which derives heat energy
from the combustion of fuel and converts it into
mechanical work is termed as a heat engine.
Heat engines may be classified into two main
types;
1) External Combustion engines (E.C engines)
2) Internal combustion engines (I.C engines)
In an external combustion engine, the
combustion of fuel takes place outside the
engine cylinder.
Ex: Steam engines
P R Venkatesh, Mech Dept, RVCE, B'lore
 In an internal combustion engine, the
combustion of fuel takes place inside the
engine cylinder.
Ex: Petrol engines, Diesel engines.
Advantages of I.C engines over E.C Engines
a) High efficiency
b) Simplicity
c) Compactness
d) Light weight
e) Easy starting
f) Comparatively low cost
P R Venkatesh, Mech Dept, RVCE, B'lore
 Classification of IC Engines:
I.C. Engines are classified according to:
1. Nature of thermodynamic cycle
Otto cycle engine.
Diesel engine.
Dual combustion cycle engine.
2. Type of the Fuel used
Petrol engine.
Diesel engine.
Gas engine.
Bi-fuel engine.
3. Number of strokes
Two stroke engine.
Four stroke engine.
P R Venkatesh, Mech Dept, RVCE, B'lore
 Classification of IC Engines (continued):
4. Number of Ignition
Spark ignition engine, known as S.I. Engine.
Compression ignition engine, known as C.I engine.

5. Number of Cylinder as
Single cylinder engine.
Multicylinder engine.

6. Position of the Cylinder

Horizontal engine.
Vertical engine.
Radial engines
In-line engines

7. Method of Cooling
Air cooled engine.
Water cooled engine.
P R Venkatesh, Mech Dept, RVCE, B'lore
 PARTS OF I C ENGINE

Outlet

Valve

Cylinder
Inlet
Piston rings

Piston
Cam
Connecting rod

Crank Case

Flywheel

Crank Shaft Crank

P R Venkatesh, Mech Dept, RVCE, B'lore
1.Cylinder:
It is made of grey cast iron.
Fuel is burnt inside the cylinder and power is developed
by action of hot gases on the piston.
To avoid wear & tear, cylinder liners are provided.

CYLINDER WITH FINS

P R Venkatesh, Mech Dept, RVCE, B'lore

2.Cylinder head:
One end of the cylinder is closed by means of a
removable cylinder head which is made of cast iron
with alloying elements such as nickel, chromium,
molybdenum, etc.
Cylinder head houses the inlet & exhaust valves.

P R Venkatesh, Mech Dept, RVCE, B'lore

3.Piston:
It is a close fitting hollow cylindrical plunger moving to &
fro inside the cylinder.
It is made of aluminium alloys for light weight.
The power developed by the combustion of fuel is
transmitted by the piston to the crank shaft through the
connecting rod.

P R Venkatesh, Mech Dept, RVCE, B'lore

4. Piston rings:
These are metallic rings made of cast iron. They are
inserted into the circumferential grooves provided at
the top end of the piston.
Piston rings maintain a gas-tight seal between the
cylinder & the piston. They also help in conducting
the heat from piston to cylinder.

PISTON , PISTON RINGS,

GUDGEON PIN & CIRCLIP

P R Venkatesh, Mech Dept, RVCE, B'lore

5. Connecting rod:
It is the link that connects the piston and the
crankshaft by means of pin joints.
It converts the linear motion of the piston into
rotary motion of the crankshaft.
Connecting rods are made of alloy steels.

CONNECTING ROD
P R Venkatesh, Mech Dept, RVCE, B'lore
CRANK & CRANK SHAFT 6. Crank & Crankshaft:
Crank is a lever (made
of carbon steel) that is
connected to the end of
the connecting rod by a
pin joint.
The other end of the
crank is rigidly
connected to a shaft
known as crankshaft.
As the connecting rod
oscillates, the crank and
hence the crankshaft
rotate about an axis.
P R Venkatesh, Mech Dept, RVCE, B'lore
VALVES 7. Valves:
Valves are devices
which control the flow
of intake and exhaust
gases to & from the
cylinder.
They are also called as
Poppet Valves and are
operated by means of
cams driven by the
crank shaft through
belts or gears.
P R Venkatesh, Mech Dept, RVCE, B'lore
 8. Flywheel:
It is a heavy wheel
mounted on the
crankshaft of the engine
to maintain uniform
RIM TYPE FLYWHEEL
rotation of the
crankshaft.
It absorbs kinetic energy
during power stroke &
delivers energy during
other strokes.
Flywheel is made of cast
DISKTYPE FLYWHEEL iron.
P R Venkatesh, Mech Dept, RVCE, B'lore
 9. Crank case:
It is the lower part of
the engine serving as an
enclosure for the
crankshaft.
It also serves as a sump
(reservoir) for
lubricating oil.

P R Venkatesh, Mech Dept, RVCE, B'lore

 I.C Engine Terminology
Cylinder cover
Valve
Clearance
Volume
TDC position
of Piston

Cylinder Stroke
Volume
Bore

BDC position
of Piston

P R Venkatesh, Mech Dept, RVCE, B'lore

 Bore: It is the inner diameter
of the engine cylinder.
Valve
Cylinder cover Stroke: It is the distance
Clearance
Volume
travelled by the piston
TDC position
of Piston when it moves from one
end of the cylinder to the
Cylinder Stroke
Volume other end. Stroke is twice
Bore the radius of crank.
BDC position
of Piston Top dead center (TDC):
In a vertical engine, it is
the topmost position of
the piston towards the
cover side of the cylinder.
In a horizontal engine, it is
called the inner dead
center. (IDC)
P R Venkatesh, Mech Dept, RVCE, B'lore
 Cylinder cover
Bottom dead center (BDC): In a
Valve
Clearance vertical engine, it is the lowest
Volume
TDC position
of Piston position of the piston towards
the crank end side of the
Stroke
Cylinder
Volume cylinder. In a horizontal
Bore
engine, it is called the outer
BDC position
of Piston dead center. (ODC)
Clearance Volume: It is the
If Vc = clearance volume &
volume contained in the
Vs Swept volume of the piston,
cylinder above the piston in
Vc Vs the top dead center position.
Compression ratio=
Vc
Compression ratio: It is the ratio
Vs
1 As Vs Vc , of total volume of the cylinder
Vc
to the clearance volume.
Compression ratio is above unity.
P R Venkatesh, Mech Dept, RVCE, B'lore
FOUR STROKE CYCLE
PETROL ENGINE

P R Venkatesh, Mech Dept, RVCE, B'lore

 FOUR STROKE CYCLE PETROL ENGINE
Petrol engines work on the
D
principle of theoretical Otto
Pressure

Reversible cycle.
adiabatic It is also known as constant
process
volume cycle, shown in fig.
C E
The piston performs four strokes
A
B (one each in half revolution of
crankshaft) to complete the
Vc Vs Volume working cycle. (in 2 revolutions
of crank shaft)
The four strokes are
P-V diagram of
(i) Suction
theoretical Otto cycle
(ii) Compression
(iii) Working (or) Power stroke
(iv)
P R Venkatesh, Mech Dept,Exhaust
RVCE, B'lore stroke
 SUCTION STROKE During suction stroke, the inlet
Exhaust valve
valve is open and exhaust valve
Inlet valve
Petrol Spark is closed.
Air mixture plug
The piston moves from cover
Cover end end to crank end during half
Cylinder revolution of crankshaft.
The air-petrol mixture is drawn
Crank end into the cylinder and completely
Piston
fills the cylinder.
Crank Shaft
Connecting
rod Suction takes place at
atmospheric pressure and is
indicated by horizontal line AB
in the p-v diagram.
SUCTION STROKE
The process is initiated by
cranking using external energy
P R Venkatesh, Mech Dept, RVCE, B'lore
source.
 During this stroke, both inlet &
COMPRESSION STROKE
exhaust valves are closed. The
piston moves from crank end to
cover end during half revolution
of crankshaft.
The air fuel mixture in the
cylinder will be compressed
adiabatically as shown by curve
BC in the p-v diagram.
At the end of compression stroke,
the air-petrol mixture is ignited by
an electric spark given out by the
spark plug.
The combustion of the mixture
COMPRESSION STROKE
causes increase in pressure as
P R Venkatesh,shown byB'lore
Mech Dept, RVCE, line CD in P-V diagram.
POWER STROKE During this stroke, both inlet &
exhaust valves are closed.
The expansion of gases due to
heat of combustion exerts a
pressure on the piston forcing it
to move towards the crank end.
The expansion of gases is
indicated by adiabatic process DE
in the P-V diagram.
At the end of this stroke, the
exhaust valve will open release
the burnt gases to the
atmosphere thus bringing down
the pressure as indicated by
POWER STROKE vertical line EB in the P-V
diagram.
P R Venkatesh, Mech Dept, RVCE, B'lore
EXHAUST STROKE During this stroke, the inlet valve
remains closed & the exhaust
Exhaust valve remains open.
gases
The piston moves from crank end
to cover end forcing exhaust
gases out of the cylinder.
The process is indicated by the
horizontal line BA in the P-V
diagram, thus completing the
cycle.
Thus the cycle is completed in
four strokes of the piston or two
revolutions of the crankshaft.
Thereafter, the entire process
repeats itself.
P R Venkatesh, Mech Dept, RVCE, B'lore
FOUR STROKE ENGINE ANIMATION

P R Venkatesh, Mech Dept, RVCE, B'lore

FOUR STROKE CYCLE
DIESEL ENGINE

P R Venkatesh, Mech Dept, RVCE, B'lore

 FOUR STROKE CYCLE DIESEL ENGINE
Diesel engines work on the
Reversible principle of theoretical Diesel
Pressure

C D
adiabatic cycle.
process
It is also known as constant
pressure heat addition cycle,
E shown in fig.
A In diesel engines the spark plug
B
is replaced by a fuel injector &
Vc Vs Volume the fuel ignites due to high
pressure & temperature of the
compressed air.
Theoretical Diesel Cycle
Hence the name CI engines.
(Compression Ignition engines)
P-V diagram of
theoretical Diesel cycleP R Venkatesh, Mech Dept, RVCE, B'lore
 SUCTION STROKE During suction stroke, the inlet
valve is open and exhaust valve
Inlet valve Exhaust valve is closed.
Fuel
injector The piston moves from cover
Air
end to crank end during half
Cover end revolution of crankshaft, and
Cylinder
draws only air into the cylinder.
The energy required for this
Crank end
stroke is obtained by cranking
Piston only at the time of starting & by
Connecting the flywheel while running.
rod
Crank Shaft
Suction takes place at
atmospheric pressure and is
indicated by horizontal line AB
in the p-v diagram.
P R Venkatesh, Mech Dept, RVCE, B'lore
COMPRESSION STROKE During this stroke, both inlet &
exhaust valves are closed. The
Fuel piston moves from crank end to
injector
cover end during half revolution
of crankshaft.
The air in the cylinder will be
compressed adiabatically as
shown by curve BC in the p-v
diagram.
At the end of compression stroke,
diesel is injected into the hot
compressed air as a fine spray by
the fuel injector.
The fuel will be burnt at constant
pressure as shown by line CD.
P R Venkatesh, Mech Dept, RVCE, B'lore
POWER STROKE During this stroke, both inlet &
exhaust valves are closed.
Fuel
injector The expansion of gases due to
heat of combustion exerts a
pressure on the piston forcing it
to move towards the crank end.
The expansion of gases is
indicated by adiabatic process DE
in the P-V diagram.
At the end of this stroke, the
exhaust valve will open release
the burnt gases to the
atmosphere thus bringing down
the pressure as indicated by
vertical line EB in the P-V
diagram.
P R Venkatesh, Mech Dept, RVCE, B'lore
EXHAUST STROKE During this stroke, the inlet valve
remains closed & the exhaust
Fuel
injector valve remains open.
Exhaust
gases
The piston moves from crank end
to cover end forcing exhaust
gases out of the cylinder.
The process is indicated by the
horizontal line BA in the P-V
diagram, thus completing the
cycle.
Thus the cycle is completed in
four strokes of the piston or two
revolutions of the crankshaft.
Thereafter, the entire process
repeats itself.
P R Venkatesh, Mech Dept, RVCE, B'lore
 TWO STROKE CYCLE ENGINE
As the name itself implies, two stroke engine performs
only two strokes of the piston or one revolution of the
crankshaft to complete one cycle.

The suction & exhaust strokes take place while the

suction & compression strokes are in progress.

The theoretical Otto cycle & Diesel cycles are followed

respectively for two stroke petrol & two stroke diesel
engines.

P R Venkatesh, Mech Dept, RVCE, B'lore

TWO STROKE CYCLE
PETROL ENGINE

P R Venkatesh, Mech Dept, RVCE, B'lore

 Spark
Spark
Plug
UPWARD STROKE Plug

Exhaust Exhaust
Port Port

Transfer Transfer
Port Port

Inlet
Port
Inlet
Port

fig (a) fig (b)

Crank Case Crank Case

During the upward stroke, the piston moves from bottom dead center to top dead
center, compressing the air-fuel mixture in the cylinder.
The cylinder is connected to a closed crank chamber.
Due to upward motion of the piston, a partial vacuum is created in the crankcase, and
fresh charge is drawn into the crank case through the uncovered inlet port.
The compressed charge is ignited in the combustion chamber by a spark plug.
P R Venkatesh, Mech Dept, RVCE, B'lore
 Spark
Plug DOWNWARD STROKE Spark
Plug

Exhaust Exhaust
Port Port

Transfer Transfer
Port Port

Inlet
Port
Inlet
Port

fig (c) fig (d)

Crank Case
Crank Case

As soon as the charge is ignited, the hot gases force the piston to move downwards,
rotating the crankshaft, thus doing useful work.
Further downward movement will uncover the exhaust port & transfer port.
The burnt gases escape through the exhaust port. The fresh charge entering through the
transfer port will be deflected by the hump provided on the piston .
It helps in removing the burnt gases completely from the cylinder and this process is
P R Venkatesh, Mech Dept, RVCE, B'lore
known as Scavenging. The cycle repeats itself thereafter.
 TWO STROKE CYCLE DIESEL ENGINE
In a two stroke diesel engine, only air is compressed in the cylinder and diesel is
injected by the fuel injector.
There is no spark plug in the engine.
The remaining operations of the engine are same as that of a petrol engine.
UPWARD STROKE
Fuel Fuel
injector injector

Exhaust Exhaust
Port Port

Transfer Transfer
Port Port

Inlet
Port
Inlet
Port

Crank CaseP R Venkatesh, Mech Dept, RVCE, B'loreCase

Crank
 DOWNWARD STROKE

Fuel Fuel
injector injector

Exhaust Exhaust
Port Port

Transfer Transfer
Port Port

Inlet
Port
Inlet
Port

Crank Case Crank Case

P R Venkatesh, Mech Dept, RVCE, B'lore

TWO STROKE ENGINE ANIMATION

P R Venkatesh, Mech Dept, RVCE, B'lore

 Comparison between Petrol Engine & and Diesel Engine
Petrol Engine Diesel Engine
1 It works on Otto cycle. It works on diesel cycle.
2 Air & petrol are mixed in the Air only enters the cylinder & diesel is
carburetor before they enter into the sprayed into the hot air.
cylinder
3 Cylinder is fitted with a spark plug. Cylinder is fitted with a fuel injector.
4 Less thermal efficiency and more fuel More thermal efficiency and less fuel
consumption. consumption.
5 Low compression ratio ranging from High compression ratio ranging from
7:1 to 12:1 16:1 to 20:1
6 Less initial cost & more running cost. More initial cost & less running cost.
7 Light weight & occupies less space. Heavy & occupies more space.
8 Easy to start even in cold weather. Difficult to start even in weather.
9 Quantitative governing is used Qualitative governing is used.
10 High engine speeds about 3000 rpm Low engine speeds about 1500 rpm.
11 Used in light vehicles like cars, motor Used in heavy duty vehicles like trucks,
P R Venkatesh, Mech Dept, RVCE, B'lore
cycles, Scoters, etc. buses, locomotives, etc.
 Comparison between 4-stroke & 2-stroke Engines
Four Stroke cycle Engine Two Stroke Cycle Engine
1 One working cycle for every two One working stroke for each revolution
revolutions of the crank shaft. of the crankshaft.
2 Requires heavy flywheel because of Requires light flywheel because of more
high torque fluctuations. or less uniform torque on crankshaft.
3 It has inlet & exhaust valves. It has inlet, exhaust & transfer ports.
4 Less fuel consumption & high More fuel consumption & lower
thermal efficiency. thermal efficiency.
5 For a given power output, the engine For the same power output, the engine
is heavy & bulky. is light & compact.
6 Requires lesser cooling & lubrication. Requires greater cooling & lubrication.
7 Less noise while running as the More noise due to sudden opening of
exhaust valves open gradually. exhaust port & release of gases.
8 Engine crankshaft can rotate only in Engine crankshaft can rotate in either
one direction. direction.
9 Mechanical efficiency is less because Mechanical efficiency is less because of
of more moving parts. less moving parts such as valves, cams.
P R Venkatesh, Mech Dept, RVCE, B'lore
10 Used in cars, buses, trucks, etc. Used in motorcycles, scooters, etc.
I C Engine Calculations

P R Venkatesh, Mech Dept, RVCE, B'lore

Indicated power (IP) :
It is the power produced inside the cylinder and calculated
by finding the actual mean effective pressure.
100Pm L A n
IP = KW
60
where Pm Mean effective Pressure in bar
L= Stroke Length in meters
A= Cross section area of cylinder bore in m 2
d2
A= where d= bore dia in meters
4
n=Number of cycles per min;
n = N for two stroke engine(N = rpm of engine)
N
n= for four stroke engine
2 P R Venkatesh, Mech Dept, RVCE, B'lore
Brake power (BP) :
It is the net power available calculated at the
crank shaft is called Brake Power.
2 NT
BP = KW
60
where N Rpm of crank shaft
T= Engine torque (in KN-m) =(W S ) R
Where W= Load on brake drum, KN
S=Spring balance reading, R=Radius of the brake drum
Also FP =(IP - BP)KW
where FP=Power lost in friction
P R Venkatesh, Mech Dept, RVCE, B'lore
Efficiencies of engine :
(i) Mechanical Efficiency :
BP
mech 100
IP
(ii) Thermal Efficiency :
Indicated therm al efficiency
IP
indicated thermal
m f CV
where m f Mass of fuel burnt in Kg/sec
CV=Calorific value of fuel in KJ/Kg
Brake thermal efficiency
BP
brake thermal
m f Dept,
P R Venkatesh, Mech
CVRVCE, B'lore
NOTE :
(i) The mean effective pressure is given by
sa 2
Pm N /m
l
where a=Area of the indicator diagram, cm 2
l Base width of indicator diagram, cm
2
s= spring constant or spring value, N/m / cm
(ii) If brake load is in kg, torque on brake drum
(9.81 W R )
T= KN - m
1000
P R Venkatesh, Mech Dept, RVCE, B'lore
BRAKE DYNAMOMETER

P R Venkatesh, Mech Dept, RVCE, B'lore

 PROBLEM 1
A single cylinder two stroke cycle I.C.
Engine has a piston diameter 105 mm
and stroke length 120 mm. The mean
effective pressure is 6 bar. If the crank
shaft speed is 1500 rpm. Calculate the
indicated power of the engine.

P R Venkatesh, Mech Dept, RVCE, B'lore

Data : N = 1500 rpm, d = 105 mm = 0.105 m
L = 120 mm = 0.12 m, Pm 6 bar,
Two stroke Number of cycles n = N 1500
Solution :
Indicated power
100Pm L A n
IP = KW
60
(0.105) 2
100 6 0.12 1500
4
IP = KW
60
IP = 15.586 KW
P R Venkatesh, Mech Dept, RVCE, B'lore
 PROBLEM 2
On a single cylinder four stroke petrol engine, the
following readings were taken:
Load on the brake drum = 40 kg.
Spring balance reading = 5 kg.
Diameter of the brake drum = 120 cm.
Fuel consumption = 3 kg/hour.
Calorific value of the fuel = 42000 kJ/kg.
Engine Speed = 500 rpm.
Find the brake thermal efficiency.

P R Venkatesh, Mech Dept, RVCE, B'lore

Data : W = 40 kg, S = 5 kg,
Dia of brake drum 2R = 120 cm
Radius of brake drum
R = 60cm = 0.6 m
Mass of fuel consumed 3kg / hr
3
mf 8.333 10 4 kg / sec
60 60
Calorific value of fuel
CV 42000 KJ / Kg
Speed of engine N=500 rpm

P R Venkatesh, Mech Dept, RVCE, B'lore

Solution :
Torque on the brake drum
9.81 (W - S) R
T= KN m
1000
9.81(40-5)0.6
T= =0.206 KN - m
1000
2 NT
Brake power BP = KW
60
2 500 0.206
BP = = 10.787 KW
60
Brake thermal efficiency
BP 10.787
brake thermal = =
m f CV 8.333 10 4 42000
brake thermal = 0.3082 = 30.82%
P R Venkatesh, Mech Dept, RVCE, B'lore
 PROBLEM 3
A gas engine working on a four stroke
cycle has a cylinder of 250 mm diameter,
length of stroke 450 mm, and is running
at 180 rpm. Its mechanical efficiency is
80% when the mean effective pressure is
0.65 Mpa.
Find 1. Indicated power, 2. Brake power
and 3. Friction power.

P R Venkatesh, Mech Dept, RVCE, B'lore

Data :
Dia of cylinder bore d = 250 mm = 0.25 m
Stroke length L=450 mm=0.45 m
SPeed N= 180 rpm, Mech 0.8
6
Pm 0.65Mpa 0.65 10 Pa
650 KPa 6.5bar
Speed of engine N=180 rpm
4-stroke n= N 180 90cycles / min
2 2
P R Venkatesh, Mech Dept, RVCE, B'lore
Solution :
Indicated power
100Pm L A n
IP = KW
60
(0.25)
2
100 6.5 0.45 90
4
IP = KW
60
IP = 21.54 KW
Also mechanical efficiency
BP
mech BP IP mech
IP
Brake power BP=21.54 0.8= 17.23 KW
Hence Power lost in friction
FP = (IP - BP) = (21.54
P R Venkatesh, Mech Dept,-RVCE,
17.23B'lore ) = 4.31 KW
 PROBLEM 4
During the test on a 4-stroke diesel engine,
the following readings were taken when
running at full load.
Area of the indicator diagram=3 cm2
Length of indicator diagram =5 cm
Spring constant = 100 N/cm2/cm
Engine crankshaft speed =500 rpm.
Diameter of the cylinder =150 mm
Stroke of the piston= 200 mm
Determine the indicated power of the engine.
P R Venkatesh, Mech Dept, RVCE, B'lore
Data :
Dia of cylinder bore d = 150 mm = 0.15 m
Stroke length L=200 mm=0.2 m
SPeed N= 500 rpm,
N 500
4 stroke Number of cycles n= 250
2 2
Spring constant s 100N/cm 2 /cm
2
Area of indicator diagram=a=3 cm
length of indicator diagram l 5cm
P R Venkatesh, Mech Dept, RVCE, B'lore
Solution :
Mean effective pressure
s a 100 3
Pm = = = 60 N / cm 2
l 5
60 N
Pm 60 10 4
N / m 2
600KPa = 6bar
(10 )-2 2

100Pm L A n
IP = KW
60
(0.15) 2
100 6 0.2 250
4
IP = KW
60
IP = 8.83 KW P R Venkatesh, Mech Dept, RVCE, B'lore
 PROBLEM 5
The following observations were made during a trial on a
4-stroke diesel engine:
Cylinder diameter =25cm
Stroke of piston =1.6 times the bore
Crankshaft speed =250 rpm
Brake load =70 kg
Brake drum diameter =2m
Mean effective Pressure =6 bar
Diesel consumption =0.1 litre/min
Specific gravity of diesel =0.78
Calorific value of diesel =43900 KJ/Kg
Determine (i) BP (ii) IP (iii) FP (iv) mech (v) I-thermal
(vi) B-thermal
P R Venkatesh, Mech Dept, RVCE, B'lore
Data :
Dia of cylinder bore d = 25 cm = 0.25 m
Stroke length L=1.6 d=1.6 0.25=0.4 m
Speed N= 250 rpm , Calorific value CV 43900 KJ / Kg
N 250
4 stroke Number of cycles n= 125
2 2
Pm 6bar , W=70 kg, 2R=2 meters R= 1meter
Given volume of fuel=0.1 litre / min =0.1 10 3 m3 / min
(As 1 m 3 = 1000litres)
Mass of fuel used per second
Volume(m 3 / min) density of fuel
mf =
60
0.1 10 3 (0.78 1000)
mf = 1.3 10 3 kg / sec
60
( Density of diesel
= specific gravity of diesel density
P R Venkatesh, Mech Dept,of
RVCE,water
B'lore (= 1000 kg / m 3 )
Solution :
(i) Indicated power :
100Pm L A n
IP = KW
60
(0.25) 2
100 6 0.4 125
4
IP = KW
60
IP = 24.54 KW
(ii) Brake power :
2 NT
BP = KW
60
9.81 70 1
2 250
1000
BP = KW
60
BP = 17.98 KWMech Dept, RVCE, B'lore
P R Venkatesh,
(iii) Frictional power :
FP =(IP - BP)=(24.54 -17.98)
FP = 6.56 KW
(iv) Mechanical efficiency :
BP 17.98
mech = 100 = 100 = 73.3%
IP 24.54
(v) Brake Thermal efficiency :
BP
B thermal = 100
m f CV
17.98
thermal = 100 = 31.5%
B
(1.3 10 ) 43900
3

(vi) Indicated Thermal efficiency :

IP
I thermal = 100
m f CV
24.54
thermal = 100 = 43%
P R(1.3 10Dept,)RVCE,
4390B'lore 0
I 3
Venkatesh, Mech
 PROBLEM 6
Find the indicated power of a four stroke
petrol engine if the average piston speed
is 70 m/min. The mean effective pressure
is 5.5 bar. The diameter of the piston is
150 mm.

P R Venkatesh, Mech Dept, RVCE, B'lore

Note:
As the piston travels a distance of 2L in one
revolution of the crank shaft,
Piston speed=2LN m/min where
L=stroke length of piston in meters
N=Rpm of crank shaft
Here, given 2LN=70 m/min.
Hence LN=35 m/min
As it is a 4 stroke engine, n=N/2
Hence Ln=17.5 m/min

P R Venkatesh, Mech Dept, RVCE, B'lore

Solution :
Indicated power :
100Pm A(Ln)
IP = KW
60
(0.15)
2
100 5.5 17.5
4
IP = KW
60
IP = 2.835 K W
P R Venkatesh, Mech Dept, RVCE, B'lore
 PROBLEM 7
A 4-stroke single cylinder I C engine of
250 mm cylinder diameter and 400 mm
stroke runs at a piston speed of 8m/sec.
If the engine develops 50 KW indicated
power, find its mean effective pressure
and the crank shaft speed.

P R Venkatesh, Mech Dept, RVCE, B'lore

Note:
As the piston travels a distance of 2L in
one revolution of the crank shaft,
Piston speed=2LN m/min where
L=stroke length of piston in meters
N=Rpm of crank shaft
Here, given 2LN=8m/sec.
i.e. 2x0.4xN=8 m/sec
Hence N=10 rps=600 rpm.
P R Venkatesh, Mech Dept, RVCE, B'lore
Solution :
Indicated power :
100Pm LA n
IP = KW
60
(0.25)
2
600
100 Pm 0.4
4 2
50 = KW
60
Pm = 5.09 bar

P R Venkatesh, Mech Dept, RVCE, B'lore