IC engine

1. Module - 2
Prime Movers
Module: 2: Prime Movers – Introduction to different types of prime movers like IC engines (4-stroke) working
principle, solving basic problems. Alternate transportation systems. E-mobility, need, advantages and
disadvantages. Configurations and its effects on existing transportation system. Turbines: Classification,
discussion on the working principles of Water Turbines [13L Hours] (Comprehension level)

2. Prime Movers
An initial source of motive power (such as a windmill, waterwheel, turbine and combustion engine or
heat engine) designed to receive and modify force and motion as supplied by some natural source
and apply them to drive machinery.

3. Heat Engine
Heat engine (Thermal engine) is a machine for converting heat, developed by burning fuel into useful work. It
can be said that heat engine is equipment which generates thermal energy and transforms it into mechanical
energy.

4. Types of Heat Engine
External Combustion
Engine
Internal Combustion
Engine
An engine in which combustion of fuel takes place outside the
engine cylinder is called external combustion engine. These
engines are generally called EC engines. Ex: Steam engines,
steam turbines
An engine in which combustion of fuel takes place inside the
engine cylinder is called internal combustion engine. These
engines are generally called IC engines. Ex: Petrol engine,
diesel engine, gas engine etc.

5. Classification of IC Engine
(i) According to the type of fuel used:
Petrol engines
Diesel engines
Gas engines
(ii) According to the number of strokes per cycle:
4-stroke engine
In this type of engines, the working cycle is
completed in four different strokes.
2-stroke engine
In this type of engines, the working cycle is
completed in two different strokes.
(iii)According to the method of ignition:
Spark ignition engine (S.I. Engine):
In this type of engines, fuel is ignited by an
electric spark generated by a spark plug.
Compression ignition engine (C.I. Engine):
In this type of engines, the fuel gets ignited as it
comes in contact with the hot compressed air.

6. (iv) According to the cycle of combustion:
Otto cycle engine
In this type of engines, combustion of fuel takes place at
constant volume.
Diesel cycle engine
In this type of engines, combustion of fuel takes place
at constant pressure.
Dual combustion engine
In this type of engines, combustion of fuel first takes
place at constant volume and then at constant pressure.
(v) According to the number of cylinders:
Single cylinder engine
Multi cylinder engine
This type of engines consists of only one cylinder.
This type of engines consists of 2, 3, 4, 6 or 8 cylinders.

7. Seven Cylinder Engine Single Cylinder Engine
(vi) According to the arrangement of cylinders
Vertical engine
Horizontal engine
Inline engine
Radial engine
V-engine

8. Vertical engine
Horizontal engine Inline engine
Radial engine V-engine

9. Parts of IC Engine
(i) Cylinder: A cylindrical vessel in which the fuel is
burnt and the power is developed. It is considered
as heart of the engine.
The primary functions of cylinder is To contain the
working fluid under pressure. To guide the piston while
reciprocating inside the cylinder.
ii) Cylinder head: The top end of the cylinder is closed by a removable component called cylinder head.
The cylinder head consists of two valves inlet valve and exhaust valve, or the other components like sparkplug, or fuel injector.
https://www.youtube.com/watch?v=Pu7g3uIG6Zo

10. (iii) Piston: A cylindrical shaped component that fits perfectly inside the engine cylinder.
The primary functions of piston include,
 To compress the charge (fuel) during the compression stroke.
 To receive the force impulse produced by the combustion of fuel, and to
transmit this force to the crankshaft through the connecting rod.
 Act as a guide (supporting member) for the upper end of the connecting rod.
 Serves as carrier of the piston rings that are used to seal the combustion
chamber from the crankcase.
(iv) Piston Rings: The rings placed in the grooves cut towards top
of the piston are called Piston Rings.
The piston rings are of two types; compression rings and oil rings.
Compression rings: The compression rings press hard with the
cylinder walls forming a tight seal between the piston and the
cylinder. This prevents escaping of the high pressure gases into the
crankcase.
Oil rings: The function of oil rings is to extract the lubricating oil
from the cylinder walls and send it back to oil sump through the
holes provided on the piston.

11. (v) Connecting rod: The connecting rod is a link that connects the piston and the crankshaft. Its
function is to convert the reciprocating motion of the piston into rotary
motion of the crankshaft.
(vi) Crank: The crank is a lever with one of its end connected to the connecting rod
by a pin joint with other end connected rigidly to the crankshaft. The
power required for any useful purpose is taken from the crankshaft.
(vii) Crank case:It encloses the crankshaft and serves as a sump for the lubricating oil.
(viii) Valves: The valves are control devices that allow the air/fuel to enter into
the cylinder and also to discharge the burnt gases to atmosphere. There are two
valves.
(a) Inlet valve (b) Exhaust valve
(a) Inlet valve is the one through which fresh charge (air and fuel or air) enters
into the cylinder.
(b) Exhaust valve through which the burnt gases are discharged out of the
cylinder. These valves are actuated by means of cams driven by the crankshaft.

12. (ix) Cams: It is an element designed to control the movement of both the inlet and exhaust valves.
(x) Flywheel: It is a heavy mass of rotating wheel or large disc mounted on the crankshaft and is
used as an energy storing device. The flywheel stores energy received during the
power stroke and supplies the same during other strokes.

13. IC Engine Terminology

14. (i) Bore: The inside diameter of the cylinder is called Bore.
(ii) Top dead center (TDC): The extreme position of the
piston near to the cylinder head is called top dead center
or TDC.
(iii) Bottom dead center (BDC): The extreme position
of the piston nearer to the crankshaft is called bottom
dead center or BDC.
(iv) Stroke: It is the linear distance travelled by the piston
from the TDC to BDC or BDC to TDC.
(v) Clearance volume (𝑽𝑪): It is the volume of cylinder
above the top of the piston, when the piston is at the
TDC.

15. (vi) Swept volume or Stroke volume (𝑽𝑺): It is the volume swept by the piston as it
moves from BDC to TDC or TDC to BDC.
(vii) Compression ratio(𝑹𝑪): The ratio of the total cylinder volume to the clearance
volume is called Compression ratio.
Total cylinder volume = Stroke volume (𝑉𝑆) + Clearance volume (𝑉𝐶)
𝐑𝐂 =
𝐕𝐒 + 𝐕𝐂
𝐕𝐂
(viii) Piston Speed: The average speed of the piston is called piston speed.
Piston speed = 2*L*N
Where; L = Stroke length in m.
N = Speed of engine in RPM.

16. Four Stroke Engine
In Four-stroke engines, piston performs four different strokes to complete all the
operations of the working cycle. The four different strokes performed are;
Suction stroke
Compression stroke
Power stroke / Expansion stroke / Working stroke
Exhaust stroke
Each stroke is completed when the crankshaft rotates by 180°. Hence in a 4-stroke engine,
four different strokes are completed through 720° of the crankshaft rotation or 2 revolutions
of the crankshaft based on the type of fuel used.

17. Four-stroke engines are classified as;
 Four-Stroke Petrol Engine.
(S.I. Engine/Constant Volume Cycle)
 Four-Stroke Diesel Engine.
(C.I. Engine/Constant Pressure Cycle)
Four-Stoke Petrol Engine
The working principle of a Four-stroke
Petrol engine is based on theoretical
Otto cycle (Constant Volume Cycle).
Hence it is also known as Otto cycle
engine (Nikolaus august Otto).

18. (a) Suction stroke:
• This stroke starts when the piston is at
TDC and about to move downwards.
• During this stroke inlet valve remains
open and exhaust valve remains
closed.
• Due to low pressure created by the
downward moving piston, the charge
(air-fuel mixture) is drawn into the
cylinder.
• At the end of this stroke the inlet
valve closes.

19. (b) Compression stroke:
• During this stroke the compression of fresh drawn charge
takes place by the return stroke (BDC to TDC) of piston.
• During this stroke both inlet and exhaust valves are closed.
• As the piston moves upwards, the air -petrol mixture in the
cylinder is compressed adiabatically. When the piston
reaches the TDC (or) just before the completion of
compression stroke, the spark plug ignites the charge.
• The compression ratio in petrol engines ranges from 7:1 to
11:1.

20. (c) Power stroke/Expansion stroke/Working stroke:
• At the beginning of the stroke, piston is in TDC and during the
stroke piston moves from TDC to BDC. During this stroke both
inlet and exhaust valves remain closed.
• The combustion of fuel liberates gases and these gases start
expanding. Due to expansion, the hot gases exert a large force on
the piston and as a result the piston is pushed from TDC to BDC.
• The power impulse is transmitted down through the piston to the
crank shaft through the connecting rod. This causes crankshaft to
rotate at high speeds. Thus work is obtained in this stroke. Hence,
this stroke is also called working stroke. Also gas expands and does
work on the piston so this stroke is also called an expansion stroke.
• As the piston reaches the BDC, the exhaust valve opens. A part of
the burnt gases escape through the exhaust valve out of the cylinder
due to their own expansion.

21. (d) Exhaust stroke:
• At the beginning of the stroke piston is in BDC and during the
stroke the piston moves from BDC to TDC.
• During this stroke inlet valve is closed and exhaust valve is opened.
• As the piston moves upward, it forces the remaining burnt gases out
of the cylinder to the atmosphere through the exhaust valve.
• When the piston reaches the TDC, the exhaust valve closes and this
completes the cycle.
• In the next cycle the piston which is at TDC moves to BDC thereby
allowing fresh charge to enter the cylinder and the process
continues.

22. Four-Stroke Diesel Engine
The working principle of a Four-stroke diesel engine is
based on theoretical diesel cycle. Hence it is also
called diesel cycle engine.
A Four-stroke diesel engine performs four different
strokes to complete one cycle.
(a) Suction Stroke
• At the beginning of the stroke piston is in TDC and during
the stroke, piston moves from TDC to BDC.
• During this stroke the inlet valve opens and the exhaust
valve will be closed.
• The downward movement of the piston creates suction in
the cylinder and as a result, fresh air is drawn into the
cylinder through the inlet valve.
• When the piston reaches the BDC, the suction stroke
completes.
(a) Suction Stroke

23. • At the beginning of the stroke piston is in BDC and during the
stroke piston moves from BDC to TDC.
• During this stroke both inlet and the exhaust valves are closed.
• As the piston moves upwards, air in the cylinder is compressed to a
high pressure and temperature.
• At the end of the stroke, the fuel (diesel) is sprayed into the
cylinder by fuel injector. As the fuel comes in contact with the hot
compressed air, it gets ignited and undergoes combustion at
constant pressure. The compression ratio ranges from 16:1 to 20:1.
(b) Compression Stroke
(b) Compression Stroke

24. • At the beginning of this stroke, piston is in TDC and during the
stroke, piston moves from TDC to BDC.
• During this stroke both inlet and the exhaust valve remain closed.
• As combustion of fuel takes place, the burnt gases expand and
exert a large force on the piston. Due to this, piston is pushed from
TDC the BDC. The power impulse is transmitted down through
the piston to the crank shaft through the connecting rod. This
causes the crankshaft to rotate at high speeds. Thus work is
obtained in this stroke.
• When the piston reaches the BDC, the exhaust valve opens. A part
of burnt gases escapes through the exhaust valve out of the
cylinder due to self expansion.
(c) Power stroke / Expansion stroke/ Working stroke :
(c) Power stroke

25. • At the beginning of the stroke piston is in BDC and during
this stroke, piston moves from BDC to TDC.
• During this stroke the inlet valve is closed and the exhaust
valve is opened.
• As the piston moves upward, it forces the remaining burnt
gases out of the cylinder through the exhaust valve. When
the piston reaches the TDC the exhaust valve closes. This
completes the cycle.
In the next cycle the piston which is at the TDC
moves to BDC thereby allowing fresh air to enter into the
cylinder and the process continues.
(d) Exhaust stroke:
(d) Exhaust stroke

26. Difference between Petrol and Diesel Engine
Petrol Engine Diesel Engine
Draws a mixture of Petrol and Air during Suction Stroke Draws only Air during Suction Stroke
Carburetor is used to mix fuel and Air in the required
proportion which and then it is supplied to the Engine
during Suction Stroke.
The injector is used to inject the fuel at the end of the
Compression stroke.
Compression ratio ranges from 7:1 to 12:1 Compression ratio ranges from 18:1 to 22:1
The Charge (Petrol air mixture) is ignited with the help of
spark plug. This type of engine is called Spark ignition
engine.
The ignition of diesel is accomplished by the compressed
air which have been heated due to high compression
ratio, to the temperature higher than the ignition
temperature of the diesel. This type of engine is called
compression ignition engine.
The combustion of fuel takes place at constant volume The combustion of fuel takes place at constant pressure.
Works on theoretical Otto cycle Works on theoretical diesel cycle

27. Power developed is less Power developed is more
Thermal efficiency is low Thermal Efficiency is High
These are High speed Engines These are low speed Engines
Maintenance Cost is less Maintenance Cost is High
Running cost is high because of higher cost of Petrol Running Cost is low because of lower cost of diesel
Lighter and cheaper because of low compression ratio Heavier and Costlier because of High Compression ratio.

28. Engine Performance Parameter
1. Indicated Power (IP):
The power available at the piston of the engine is called
indicated power. It is denoted by IP and is expressed in kW
(Kilowatts)
Mathematically,
Indicated Power (IP) = 𝒏𝑷𝒎𝑳𝑨𝑵𝑲
𝟏𝟎
𝟔
𝐤𝐖
2. Brake Power (BP):
The power available at the Crankshaft of the
engine is called Brake power. It is denoted by
BP and is expressed in kW (Kilowatts)
Mathematically ,
𝑩𝑷 =
𝟐𝝅𝑵𝑻
𝟔𝟎 ∗ 𝟏𝟎𝟎𝟎
𝐤𝐖
Where, N is the speed of the Engine
in RPM
T is the Torque in Nm

29. 3. Friction Power (FP):
The amount of power lost due to friction of the
moving parts inside the engine cylinder is called
friction power. Friction power is the difference
between indicated power and brake power. It is
denoted by FP and expressed in kW.
FP = IP –BP (kW)
Where, IP = Indicated Power
BP = Brake Power
4. Indicated Mean Effective Pressure (Pm):
It is the mean or average pressure acting on the
piston during the power stroke.
5. Mechanical Efficiency (𝜼𝒎𝒆𝒄𝒉):
It is defined as the ratio of Brake power to the
Indicated power.
𝜼𝒎𝒆𝒄𝒉 =
𝑩𝑷
𝑰𝑷
*100
6. Thermal efficiency (𝜼𝒕𝒉):
It is defined as the ratio of power output to the heat supplied by combustion of fuel.
𝜼𝒕𝒉 =
𝑷𝒐𝒘𝒆𝒓 𝒐𝒖𝒕𝒑𝒖𝒕
𝑯𝒆𝒂𝒕 𝒔𝒖𝒑𝒑𝒍𝒊𝒆𝒅
*100
Heat supplied = mf * CV in kJ/sec
Where, mf = Mass of fuel in kg/sec
CV = calorific value of fuel in kJ/kg
The power output may be indicated power (IP) or Brake power (BP).

30. 6. (a) Indicated Thermal efficiency(𝜼𝑰𝒕𝒉
):
It is defined as the ratio of indicated power to the
heat supplied by combustion of fuel.
𝜼𝑰𝒕𝒉
=
𝑰𝑷
𝒎𝒇 ∗ 𝑪𝑽
∗ 𝟏𝟎𝟎
6. (b) Brake Thermal efficiency(𝜼𝑩𝒕𝒉
):
It is defined as the ratio of brake power to the heat
supplied by combustion of fuel.
𝜼𝑩𝒕𝒉
=
𝑩𝑷
𝒎𝒇 ∗ 𝑪𝑽
∗ 𝟏𝟎𝟎
(7) Brake Specific Fuel Consumption (BSFC):
It is defined as the mass of the fuel consumed in
one hour by an engine in developing 1 kW of brake power.
This can be expressed as
𝑩𝑺𝑭𝑪 =
𝑴𝒂𝒔𝒔 𝒐𝒇 𝒕𝒉𝒆 𝒇𝒖𝒆𝒍 𝒄𝒐𝒏𝒔𝒖𝒎𝒆𝒅 𝒊𝒏 𝒌𝒈/𝒉𝒓
𝑩𝒓𝒂𝒌𝒆 𝒑𝒐𝒘𝒆𝒓 𝒅𝒆𝒗𝒆𝒍𝒐𝒑𝒆𝒅 𝒊𝒏 𝒌𝑾
𝐤𝐠 / 𝐤𝐖 − 𝐡𝐫