Internal Combustion Engine.
(I C Engine)
Dept. of Mech & Mfg. Engg.
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Classification of I C Engines
• According to:
• (i) Nature of Thermodynamic Cycle :
– 1. Otto cycle engine.
– 2. Diesel cycle engine.
– 3. Dual combustion cycle engine.
• (ii) Type of the Fuel- used :
–
–
–
–
–
1. Petrol engine.
2. Diesel engine.
3. Gas engine.
4. Bi-fuel Engine.
5. Dual Fuel Engine
Dept. of Mech & Mfg. Engg.
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Classification of I C Engines
(iii) Number of Strokes :–
–
1. 2 - stroke engine
2. 4 - stroke engine
(iv) Method of Ignition:
–
–
1. Spark ignition engine, [S.I. Engine].
2. Compression ignition engine, [C.I. engine].
(v) Number of Cylinders
–
–
1. Single cylinder engine.
2. Multi-cylinder engine.
Dept. of Mech & Mfg. Engg.
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Classification of I C Engines
•
(vi) Position of the Cylinder:
–
–
–
–
•
1. Horizontal engine
2. Vertical engine
3. V- engine.
4. Radial engine.
(vii) Method of Cooling :
–
–
•
1. Air cooled engine.
2. Water cooled engine
(viii) Speed of the Engine :
–
1. Low speed engine.
–
2. Medium speed engine.
–
3. High speed engine.
Dept. of Mech & Mfg. Engg.
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I C Engine Parts
Dept. of Mech & Mfg. Engg.
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I C Engine terms & Definition
Spark plug
TDC (top dead center):
It is the top most position
of the piston towards
head side of the cylinder
Valve
Clearance
volume
TDC
Bore
Stroke
BDC (bottom dead center):
The lowermost position of
the piston towards the
crank end side of the
cylinder.
BDC
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Piston
6
Stroke:
It is the linear distance
traveled by the piston
when it moves from one
end of the cylinder to the
other end
Bore:
It is the
inside diameter
of the
cylinder.
Dept. of Mech & Mfg. Engg.
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Swept volume or
(Displacement volume)
It is the volume swept
through by the piston in
moving between TDC and
BDC
Clearance volume:
It is the volume contained
in the cylinder above the
top of the piston, when the
piston is at TDC.
Dept. of Mech & Mfg. Engg.
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Total volume = swept volume + clearance volume.
Compression ratio: “r”
It is the ratio of total cylinder volume to clearance
volume.
r = Total volume
clearance volume
Value of “r” for,
petrol engine lies between 7 to 9
Diesel engine lies between 15 to 22
Dept. of Mech & Mfg. Engg.
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Working of 4-S Petrol engine
• The petrol engines work on the principle of
“OTTO CYCLE”, also known as constant
Volume cycle.
• The engines operating on this cycle use
either petrol or other spirit fuels or the
gases such as LPG / CNG as their fuels.
Dept. of Mech & Mfg. Engg.
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•
•
In a 4-Stroke petrol engine, the charge is
admitted to the engine cylinder is a
homogeneous mixture of petrol and air.
Depending on the load on the engine,
the fuel and air is mixed in proper
proportions and sent in to the cylinder by
a popular device known as “carburetor”.
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In a 4-stroke petrol engine there are four
main events taking place, they are
1. Suction
2. Compression
3. Working or power or expansion, and
4. Exhaust
So in a cycle there are four events to take
place, and each of this is performed
during a single stroke of the piston
Since ignition in these engines is due to a spark,
they are also called spark ignition engines .
Dept. of Mech & Mfg. Engg.
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Dept. of Mech & Mfg. Engg.
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1. INTAKE [Suction]: During the intake stroke, the
piston moves down ward, drawing a fresh charge of
vaporized fuel-air mixture, This operation is
represented by the line AB on the P-V diagram.
Pressure [P]
TDC
BDC
A
B
Volume [V]
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2. Compression Stroke: During compression stroke, the piston
moves from BDC to TDC, thus compressing air petrol mixture. Due to
compression, the pressure and temperature are increased and is shown by
the line BC on the P- V diagram. Just before the end of this stroke the spark
- plug initiates a spark which ignites the mixture and combustion takes place
at constant volume as shown by the line CD
Pressure [P]
D
TDC
C
BDC
A
B
Volume [V]
Dept. of Mech & Mfg. Engg.
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3. Working Stroke: The expansion of gases due to
the heat of combustion exerts a pressure on the
piston. Under this impulse, the piston moves from
TDC to BDC and thus the work is obtained in this
stroke as shown by the line DE
Pressure [P]
D
TDC
C
E
BDC
A
B
Volume [V]
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4. Exhaust Stroke: At the end of the power stroke, the exhaust valve is
opened & greater part of the burnt gases escapes because of their
own expansion. The drop in pressure at constant volume is
represented by the line EB. During this stroke the piston moves from
BDC to TDC and pushes the remaining gases to the atmosphere. This
stroke is represented the line BA on the P-V diagram.
Pressure [P]
D
TDC
C
E
BDC
A
B
Volume [V]
Dept. of Mech & Mfg. Engg.
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P V diagram for
SI Engine / Otto cycle engine
D
D
TDC
C
Pressure
E
A
BDC
B
Volume
Theoretical Otto cycle
Dept. of Mech & Mfg. Engg.
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Working of 4-S Diesel engine
The basic construction of a four stroke
diesel engine is same as that of four stroke
petrol engine.
Except that instead of a spark plug, a fuel
INJECTOR is mounted in its space.
Fuel injector injects the fuel in to the
cylinder as a fine spray at very high
pressure
Dept. of Mech & Mfg. Engg.
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In case of diesel engine, the air enters the inside
the cylinder during suction, and it will get
compressed during the compression stroke. (i.e..
charge is only air)
At the end of the compression stroke the diesel is
injected in to the cylinder in the form of fine spray
When this fine spray diesel comes in contact with
hot air in the cylinder, it auto ignites and results in
a combustion of injected diesel fuel.
Since ignition in these engines is due to the
temperature of the compressed air, they are also
called compression ignition engines.
Dept. of Mech & Mfg. Engg.
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1. INTAKE [Suction]: During the intake
stroke, the piston moves down ward,
drawing a fresh charge [AIR]. This
operation is represented by the line AB on
the P-V diagram.
Pressure [P]
TDC
BDC
A
B
Volume [V]
Dept. of Mech & Mfg. Engg.
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2. Compression Stroke: During compression
stroke, the piston moves from BDC to TDC, thus
compressing air. Due to compression, the
pressure and temperature are increased and is
shown by the line BC on the P- V diagram. Just
before the end of this stroke, aDmetered quantity
of Diesel is injected intoC the hot compressed air
[P]
in the form ofPressure
fine sprays
by means of fuel
injector. TDC
The fuel starts burning at constant
pressure shown by the line CD.
BDC
A
B
Volume [V]
Dept. of Mech & Mfg. Engg.
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3. Working Stroke: The expansion of gases
due to the heat of combustion exerts a
pressure on the piston. Under this impulse,
the piston moves from TDC to BDC and
thus the work is obtained
inD this stroke as
C
shown by the
line DE
Pressure [P]
TDC
E
BDC
A
B
Volume [V]
Dept. of Mech & Mfg. Engg.
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4. Exhaust Stroke: At the end of the power stroke,
the exhaust valve is opened & greater part of the
burnt gases escapes because of their own
expansion. The drop in pressure at constant
volume is represented by the line EB. During this
D
C
stroke the piston moves from BDC to TDC and
pushes the remaining
Pressure [P] gases to the atmosphere.
TDC is represented the line BA on the P-V
This stroke
diagram.
E
BDC
A
B
Volume [V]
Dept. of Mech & Mfg. Engg.
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P V diagram for
CI Engine / Diesel cycle engine
D
C
D
TDC
Pressure
E
A
BDC
B
Volume
Theoretical Diesel cycle
Dept. of Mech & Mfg. Engg.
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Comparison between Petrol & Diesel
Engine
1
Petrol engine
Diesel engine
It works on Otto cycle. It works on diesel cycle.
2
Air and petrol are
mixed in the
carburetor before they
enter into the cylinder.
Diesel is fed into the
cylinder by fuel injection
and is mixed with air
inside the cylinder.
3
It compresses a
mixture of air and
petrol and is ignited by
an electric spark.
(Spark Ignition)
It compresses only air
and ignition is
accomplished by the
heat of compression.
(Compression Ignition)
Dept. of Mech & Mfg. Engg.
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4
Cylinder is fitted with a
spark plug.
Cylinder is fitted with a
fuel injector.
5
Less thermal efficiency More thermal efficiency
and more fuel
and less fuel
consumption.
consumption.
6
Compression ratio
ranges from 4:1to10:1
Compression ratio
ranges from 12:1 to 22:1
7
Less initial cost and
more running cost.
More initial cost and less
running cost.
8
Light weight and
occupies less space.
Heavy and occupies
more space.
Dept. of Mech & Mfg. Engg.
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9
10
11
12
Difficult to start in cold
Easy to start even in
weather and requires
cold weather.
heater plugs.
They run for longer
Requires frequent
periods between
overhauling.
overhauls.
Fuel (petrol) is
Fuel (diesel) is cheaper
costlier and more
and less volatile.
volatile.
Used in light
Used in heavy duty
vehicles like cars,
vehicles like tractors,
motor cycle,
trucks, buses,
scooters, etc.
locomotives, etc.
Dept. of Mech & Mfg. Engg.
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Working of the Two Stroke
engine.
In a two stroke engine, a cycle is
completed by the two strokes of the piston.
Out of the four strokes, the two strokes
that are eliminated are, suction and
exhaust strokes.
However, the exhaust process is achieved
by the admission of charge which is
extremely compressed, which drives out
the burnt gases out and this process is
popularly called as SCAVENGING.
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In case of the two stroke engines instead of
valves, ports are used.
Ports in the cylinder liner, opened and closed by
the piston motion itself
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Working of Two Stroke Petrol
Engine
First stroke
First stroke
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Working of Two Stroke Petrol
Engine
• First stroke (Downward) As
soon as the charge is ignited,
the hot gases force the piston
to move downwards, rotating
the crankshaft, thus doing the
useful work. During this stroke
the inlet port is covered by the
piston and the new charge is
compressed in the crank case
as shown in the fig.
Dept. of Mech & Mfg. Engg.
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• Further downward movement of the piston uncovers
first the exhaust port and then the transfer port.
• The burnt gases escape through the exhaust port.
• As soon as the transfer port opens,
the compressed charge from the
crankcase flows into the cylinder.
• As the compressed charge enters
into the cylinder, it pushes out the
exhaust gases from the cylinder.
• The process of removal of exhaust
gases by the fresh incoming
charge is known as scavenging.
Dept. of Mech & Mfg. Engg.
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• Second stroke: (upward)
Here the piston moves from
BDC to TDC, during the
process the exhaust port and
transfer port are covered and
the charge in the cylinder is
compressed. Simultaneously,
vacuum is created in the
crankcase, and a new charge
is drawn into the crankcase
through the uncovered inlet
port.
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• The compressed
charge is ignited in the
combustion chamber
by a spark provided by
the spark plug and the
cycle of events is then
repeated.
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Working of Two Stroke Diesel
Engine
First stroke
Second stroke
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• First stroke (Downward)
Combustion starts once the
diesel is injected in to the hot
compressed air, the hot gases
force the piston to move
downwards, rotating the
crankshaft, thus doing the
useful work. During this stroke
the inlet port is covered by the
piston and the new charge [air]
is compressed in the crank
case as shown in the fig.
Dept. of Mech & Mfg. Engg.
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• Further downward movement of the piston
uncovers first the exhaust port and then the
transfer port.
• The burnt gases escape through the exhaust port.
• As soon as the transfer port opens,
the compressed charge from the
crankcase flows into the cylinder.
• As the compressed charge enters
into the cylinder, it pushes out the
exhaust gases from the cylinder.
• The process of removal of exhaust
gases by the fresh incoming air is
known as scavenging.
Dept. of Mech & Mfg. Engg.
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• Second stroke: (upward)
Here the piston moves from
BDC to TDC, during the
process the exhaust port
and transfer port are
covered and the fresh air in
the cylinder is compressed.
Simultaneously, vacuum is
created in the crankcase,
and a new charge [air] is
drawn into the crankcase
through the uncovered inlet
port.
Dept. of Mech & Mfg. Engg.
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• At the end of the compression diesel is injected
to the compressed air which is at a temperature
higher than the self ignition temperature of
diesel. Hence, the injected diesel auto ignites
when it comes in contact with hot air. And the
cycle of events is then repeated.
Dept. of Mech & Mfg. Engg.
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Comparison between 4 - stroke &
2 - stroke Engine
1
2
3
4 – stroke engine
One Working stroke for
every two revolution of
the Crank shaft
Turning moment on the
crank shaft is not even,
hence heavier flywheel
is required
2 – stroke engine
One working stroke for
each revolution of the
crank shaft
Turning moment on the
crank shaft is more
even, hence lighter
flywheel is required
Less fuel consumption More fuel consumption.
Dept. of Mech & Mfg. Engg.
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6
Engine design is
complicated
Less output due to
mixing of fresh charge
with the burnt gases.
Lower thermal
efficiency
Engine design is
simple.
7
Lesser rate of wear and
tear.
Greater rate of wear
and tear.
8
It has inlet and exhaust
valves
It has inlet and exhaust
ports
4
5
More output due to full
fresh charge intake and
full burnt gases exhaust.
Higher thermal efficiency
Dept. of Mech & Mfg. Engg.
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9
10
11
12
13
Engine is heavy &
bulky.
It requires lesser
cooling and
lubrication
More initial cost
For the same power, the
engine is light and
compact.
It requires greater cooling
and lubrication. (consumes
more lubricating oil)
Less initial cost.
More running noise due to
Less running noise the sudden release of the
burnt gases.
Used in cars,
Used in mopeds, motor
trucks, buses,
cycles, scooters, etc.
tractors, etc.
Dept. of Mech & Mfg. Engg.
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Important definitions
• Brake Power [B.P]: It is the power developed by
the engine at the output shaft.
2NT
Brakepower , 
kw
60000
Where, N = Speed of the crank shaft in rpm.
T =Torque applied on the brake drum due to load “W”, (N-m)
R = Radius of the brake drum (m)
T = W x R kg-m
= 9.81 x W x R N-m
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• Indicated Power [I.P]: It is the power
developed inside the IC engine cylinder
i  Pm  L  A  n
Indicatedpower, 
kW
60000
Where, n = No. of working cycles/ min.
,
n = N/2, for 4 stroke engine
= N, for 2 stroke engine
L = Stroke length (m), D = Bore diameter (m)
Pm = Indicated mean effective pressure (N/m2)
 2 2
A = Area of the cylinder, A  D , m
4
Dept. of Mech & Mfg. Engg.
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• Frictional Power [F.P]: It is the difference between
the indicated power and the brake power.
F.P = [I.P – B.P] kW
,
• Mechanical Efficiency [ηmech ]: It is the ratio of the
brake power and the indicated power.
Mechanical efficiency , mech
B.P

 100 %
I .P
Dept. of Mech & Mfg. Engg.
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• Brake thermal Efficiency [ηbth ]: It is the ratio of
the brake power to the heat supplied by the fuel.
B. P  3600
 bth 
*100%
mf  Cv
• Indicated thermal Efficiency [ηith ]:
It is the ratio of the indicated power to the heat
supplied by the fuel.
I.P  3600
 ith 
*100%
mf  Cv
Where, mf = mass of the fuel supplied (kg/hr)
CV = Calorific Value of the fuel (kJ/kg)
Dept. of Mech & Mfg. Engg.
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Working of a Simple Carburetor
• The petrol enters the float chamber through the needle valve,
Purpose of needle valve is to maintain the constant level of
petrol in the float chamber.
• When engine runs, the air is
sucked through the venturi tube.
As a result pressure at throat
reduces (-) and the petrol issues
out of the main jet located at the
throat.
• Thus amount of petrol issuing
from jet proportional to the
velocity of air through the venturi
tube.
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Working of a Diesel pump
• Plunger of the fuel pump is operated by the cam roller
mechanism, which derives the power from the engine. El.
• As plunger moves up, the fuel filled above the plunger is
pressurized and pressurized fuel flow through the barrel.
• The outlet of from the fuel pump
barrel is closed by a spring loaded
delivery valve which opens only at
prescribed pressure of the fuel.
• As the fuel pressure rises, the
delivery valve and is forced out
towards the injector.
Dept. of Mech & Mfg. Engg.
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Working of a Diesel injector
• Fuel under pressure from the
pump, passes down through
passages in the injector body
to an annular space in the
nozzle and lifts the needle
valve against pressure of the
spring
• As a result fuel is forced
through the holes of injector
under high pressure resulting
in finely atomized spray.
Dept. of Mech & Mfg. Engg.
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