The document provides information on types of heat engines, including internal and external combustion engines. It then discusses key components of internal combustion (IC) engines like the cylinder block, cylinder head, piston, combustion chamber, camshaft, valves, piston rings, connecting rod, crankshaft, and flywheel. It also defines 4-stroke engines and compares spark ignition (SI) and compression ignition (CI) engines. Finally, it explains the construction and working of 4-stroke petrol/diesel engines and 2-stroke petrol/diesel engines through their intake, compression, power/expansion, and exhaust strokes.

1. SHARAD INSTITUTE OF TECHNOLOGY COLLEGE OF
ENGINEERING, YADRAV
Prof. Avesahemad S. N. Husainy Assistant Professor, Department of Mechanical Engineering
Member of ISHRAE and ASHRAE
(Applied Thermodynamics-II)
I.C.Engine (Unit No: 01)
https://www.youtube.com/channel/UCPVNu2txpcsFU2eZf0DPRsg
linkedin.com/in/avesahemad-husainy-54507aa3
https://classroom.google.com/w/NTYyMjQxO
Class Code: on4uvhh
Prof. Avesahemad S. N. Husainy, Assistant Professor, Department of Mechanical Engineering
Member of ISHRAE and ASHRAE

2. Definition of Heat Engine:
In thermodynamics, a heat engine is a system that converts heat or thermal energy and chemical energy to
mechanical energy which can then be used to do mechanical work.
Types of Heat Engine:
1. Internal Combustion Engine- Car Engine
2. External Combustion Engine-GasTurbine
In an "internal combustion engine" the fuel mixes with an oxidizer and burns inside the engine. In an
"external combustion engine" the fuel mixes with an oxidizer and burns outside the engine.
Applications:
Introduction

3. Terminology of I. C. Engine

4. • Cylinder Block
It is the heart of the engine.
It consists of three parts.
(i)The cylinders in which the piston slides up and down.
(ii)The ports or openings for valves.
(iii)The passages (water jackets) for the flow of cooling water.
Material: Aluminum alloy and grey cast iron.
• Cylinder Head:
It is fitted on the top of the cylinder.
It has inlet valve, exhaust valve and the spark plug or fuel
injector.
Material: Grey cast iron, Aluminum alloy and cast steel.
• Piston:
It is the main active part of the engine. It is cylindrical in
construction and slides up and down inside the cylinder.
Function:
To compress the fresh charge during the compression stroke.
Material: Aluminum alloy cast steel, cast iron and chrome
nickel
• Combustion Chamber:
The space enclosed in the upper part of the cylinder, by the
cylinder head and the piston top during the combustion
process, is called the combustion chamber.
Combustion chamber is the closed space in which combustion
of fuel takes place.
• Camshaft:
A camshaft is a shaft on which cams are mounted.
The camshaft is driven by crankshaft through timing gears.
Function: It is used to operate the intake and exhaust valves
through cam follower, push rod and rocker arm.
Material: Forged steel.
• Inlet and ExhaustValves:
Function
(i) Inlet valve allows the fresh charge into the cylinder.
(ii) Exhaust valve provides passages for the burnt gases to escape from
the cylinder.
Piston Rings:
Piston rings are fitted into the grooves of the piston to maintain good
seal between the piston and the cylinder walls.
Function:
Compression rings are used to provide gas tight sealing to prevent
leakage of the lubricating oil into the engine cylinder.
Material: Alloy cast iron containing silicon, manganese, alloy steels,
Connecting Rod:
The connecting rod interconnects the piston to the crankshaft. The upper
end of the connecting rod is fitted to the piston and lower end to the
crankshaft.
Function:
It transmits the power produced in the cylinder to the crankshaft.
Material: Medium carbon steel and alloy steel.
• Crank and Crankshaft
The crank is a lever that is connected to the end of the connecting rod by
a pin joint with its other end connected rigidly to a shaft, called
crankshaft.
Function: It converts the reciprocating motion of the piston into useful
rotary motion of the Output Shaft.
Material: Forged steel.
• Flywheel:
Function: The flywheel stores the excess energy during the power stroke
of the engine and supplies the energy for the movement of the piston
during the remaining stroke.
Material: Cast iron

5. Classification of Engine

6. Difference between SI and CI engine

7. Construction and Working of 4 Stroke Petrol Engine

8. (a) Suction Stroke:
During the suction stroke, the inlet valve is kept opened and the exhaust valve remains closed. The piston travels from TDC
to BDC in case of vertical cylinder engine. The suction pressure is found little less than the atmospheric pressure. During
this stroke, a mixture of petrol vapor and air (prepared by carburetor) in correct proportion is drawn into the cylinder.
(b) Compression Stroke:
During the compression stroke, both the inlet and exhaust valves are closed. The mixture of petrol vapor and air already
drawn in suction stroke is compressed when the piston returns from BDC towards TDC. The compression ratio in the case
of SI engines is 6-9. At the end of compression stroke, since the temperature achieved is less than the ignition temperature
of petrol, sparking is done instantaneously by spark plug, and thus, the compressed mixture is ignited with the help of
electric spark. In this case, there is an ignition system which does this work at proper timing. The combustion starts leading
to high temperature and pressure. The fuel starts burning. During this combustion phenomenon, the chemical energy of
fuel is converted into heat energy producing nearly 2000°C
(c) Expansion Stroke or Power Stroke:
During the power stroke, inlet and exhaust valves stay closed. The piston moves from TDC to BDC and the crankshaft
completes half revolution. High-pressure burnt gases push the piston towards BDC.
The reciprocating motion of the piston causes to produce mechanical work which is transferred to the crankshaft through
connecting rod. As the piston moves towards the BDC, the pressure of burnt gases decreases gradually. When the piston
reaches BDC, the exhaust valve is almost open
(d) Exhaust Stroke:
During this stroke, the inlet valve is closed and the exhaust valve is opened. The piston moves from BDC to TDC and the
crankshaft revolves half revolution. As the piston moves up, the burnt gases are expelled out from the cylinder.
This movement of the piston is done by the inertia effect of the flywheel, Fly wheel is a heavy weight wheel mounted on
shaft which has high moment of inertia. During operation, the fly wheel absorbs energy which is supplied during this
period.

9. Construction and Working of 4 Stroke Diesel Engine

10. (a) Suction Stroke:
During this stroke, the inlet valve is kept opened and the exhaust valve remains closed. The piston moves
from TDC to BDC in vertical cylinder engine. The suction pressure is found little less than the atmospheric
pressure. During this stroke, a fixed amount of air is sucked in the cylinder through the opening of an inlet
valve. At the end of this stroke, the entire cylinder is filled with air.
(b) Compression Stroke:
During this stroke both the valves are kept closed. The piston moves from BDC to TDC. The amount of air
which was sucked during the suction stroke is compressed during the compression stroke. The piston
returns back from BDC to TDC. The compression ratio in this case varies from 11 to 22. The compression
ratio in CI engine is high as compared to that in SI engine.
At the end of compression process, pressure and temperature are very high. The temperature achieved is
more than the ignition temperature of diesel which is more than the ignition temperature of petrol in SI
engine. When the compression ends, the diesel fuel is injected in the form of spray by the injector. As soon
as the diesel particles come in contact with the high-temperature compressed air, they catch fire
instantaneously.
(c) Expansion Stroke:
The downward movement of piston towards BDC causes to develop mechanical work which is transferred
to the crankshaft through connecting rod. As the piston moves down, the gas pressure gradually
decreases. This is an expansion stroke. Now the entire cylinder is filled with hot gases, only to be expelled
out for fresh cycle to continue.
(d) Exhaust Stroke:
During this stroke, both inlet and exhaust valves are closed. Piston starts moving from BDC to TDC which
pushes out the product of combustion. Due to high pressure achieved in the cycle, the CI engine is
considered stronger than SI engine.

11. Construction and Working of 2 Stroke Petrol Engine

12. The principle of two stroke spark ignition engine is shown in the figure. Its two strokes are as follows:
• Upward Stroke
• Downward Stroke
Upward Stroke
During upward stroke, the piston moves upward from the bottom dead center to top dead center. By compressing
the charge air petrol mixture in the combustion chamber of the cylinder. Due to upward movement of the piston, a
partial vacuum is created in the crankcase. And a new charge is drawn into the crankcase through the uncovered inlet
port. The exhaust port and transfer port are covered when the piston is at the top dead center position. The
compressed charge is ignited in the combustion chamber by a spark given by the spark plug.
Downward Stroke
As soon as the charge is ignited the hot gases compress the piston which moves downward, 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 crankcase. Further downward movement of the piston uncovers first the exhaust port and then
the transfer port. and hence the exhaust starts through the exhaust port. As soon as transfer port is open, the charge
through it is forced into the cylinder. The charge strikes the deflector on the piston crown, rises to the top of the
cylinder and pushes out most of the exhaust gases. The piston is now at the bottom dead center position. The
cylinder is completely filled with a fresh charge, although it is somewhat with the exhaust gases. The cycle of events
is then repeated, the piston making two strokes for each revolution of the crankshaft.

13. Construction and Working of 2 Stroke Diesel Engine
I st Stroke
During this stroke piston move upward direction(piston
moves from bottom dead centered to top dead centered ).
This time inlet port is open and exhaust and transfer port
are closed. This time air entered into the crank case also air
which is already inside the cylinder. This air is compressed to
very temperature and pressure at this state fuel injected by
fuel injector fuel start burning.
II nd Stroke
The high pressure is developed due to the burning of the
fuel and the pushed the piston down wards(piston moves
from top dead centered to bottom dead centered). During
this down ward stroke exhaust and transfer port are open
and inlet port is closed. This time air from crank case will
enter in to the cylinder throw transfer port. Also burning gas
will escape through exhaust port or escape port.