The document discusses internal combustion engines. It defines them as engines where combustion occurs inside the engine cylinder. It then describes the basic parts of an I.C. engine like the cylinder, piston, crankshaft. It explains the differences between a 2-stroke and 4-stroke engine and how their cycles work. A 2-stroke engine completes one cycle per revolution while a 4-stroke takes two revolutions. It provides details on the workings and compares the advantages and disadvantages of 2-stroke and 4-stroke diesel engines.

1. GOVERMENT ENGINEERING COLLEGE
GANDHINAGAR

2. -: TOPIC :-
 What is I.C. Engine?
 Basic parts of I.C. Engine.
 What is stroke ?
 What is 2-stroke & 4-stroke ?
 Working of 2-stroke Diesel Engine.
 Advantages & Disadvantages.
 Working of 4-stroke Diesel Engine.
 Advantages & Disadvantages.
 Comparison of 2-stroke & 4-stroke cycle engine.

3. What is I.C. Engine ?
I.C. Engines means internally combustion engines.
All those engines in which combustion of the fuel
release heat energy inside the engine cylinder are
known as “Internal Combustion Engines”.
These engines are widely used as prime movers and
also in road vehicles, locomotives, industrial
applications.
Examples : Petrol engines, Diesel engines and Gas
engines.

4. Basic parts of I.C. Engine ?
1. Cylinder
2. Cylinder head
3. Piston
4. Connecting rod
5. Crank shaft
6. Cam shaft
7. Fly wheel

5. 1. Cylinder :-
 It is the important part of this engine in which the
piston moves up and down in order to develop power.
2. Cylinder head :-
 It is fitted one end of the cylinder and act as a cover to
close the cylinder.
 It contains : Inlet valve & Outlet valve.
Spark plug or injector.
3. Piston :-
 It is considered as the heart of I.C engine. Whose main
function is to transmit the force exerted by the burning
of charge to the connecting rod.

6. 4. Connecting rod :-
 It is the link between the piston and crank shaft.
Whose main function is to transmit force from the
piston to the crank shaft.
5. Crank shaft :-
 It is considered as the backbone of an I.C Engine.
Whose function is to convert reciprocating motion of
piston in to the rotary motion with the help of
connecting rod.
6. Cam shaft :-
 The shaft which has cams for the opening and closing
of inlet & outlet valves.

7. 7. Fly wheel :-
 It is the big wheel mounted on the crankshaft whose
function is to maintain speed at constant.
 The constant speed is done by storing excess energy
during power stroke up to returning of other power
stroke.

8. What is Stroke ?
Reciprocating motion, used in reciprocating engines
and other mechanisms, is back and forth motion.
Each cycle of reciprocation consists of two opposite
motions : there is a motion in one direction, and then
a motion back in the opposite direction. Each of these
is called a “Stroke”.

9. What is 2-stroke & 4-stroke?
A two stroke diesel engine is an internal combustion
engine that completes the process cycle in one
revolution of the crank shaft. Thus, one power stroke is
obtained in each revolution of the crank shaft.
A four stroke diesel engine is an internal combustion
engine that completes the process cycle in two
revolution of the crank shaft. Thus, one power stroke is
obtained in each two revolutions of the crank shaft.

10. 2-Stroke Diesel Engine :-
Working :-
In this engine the piston moves down on the power
stroke. It first uncovers the exhaust port. The cylinder
pressure drops to atmospheric pressure as the
combustion products leave the cylinder.
Further movement of piston uncovers the transfer port.
As soon as the transfer port opens, the slightly
compressed air in the crank case enters into cylinder.
The piston is so shaped that the fresh air will sweep up
to the top of the cylinder and push out the remaining
gases through exhaust port.

11. During compression stroke, first the transfer port closes
and compression of the air begins. This movement
lowers the pressure into the crank case. Thus, the
atmospheric air enters through inlet valve in the crank
case.
Before the end of the compression stroke the fuel is
injected from the injector into hot air. The ignition of the
fuel starts and combustion goes as long as the nozzle is
open. When the piston is near the BDC , the piston
uncovers exhaust port which permits the gases to floe
out of cylinder.

13. Advantages :-
 One cycle completed in every revolution of crankshaft.
 Compact, required less space & lighter weight.
 Design & construction is simpler than 4-stroke engine.
 Easy to manufacture & low cost.
Disadvantages :-
 High fuel consumption.
 Compression ratio & thermal efficiency is less than four
stroke engine.
 Consumes more lubricating oil.
 More wear & tear of moving parts hence it gives loud noise.

14. 4-Stroke Diesel Engine :-
Working :-
The working of diesel engine based on diesel cycle or
constant pressure combustion cycle as the combustion of
fuels place at constant pressure.
The cycle is completed in 4 strokes.
During suction stroke, the inlet valve remains open &
exhaust valve remains closed. The piston moves from TDC
to BDC. Air from the atmosphere is drawn into the cylinder.
During compression stroke, inlet and outlet valve remains
closed. Piston moves from BDC to TDC. The air
compressed to high pressure & temperature.

15. During expansion stroke, both valve remains closed and
the piston moves from TDC to BDC. Fuel injected in the
cylinder causes the combustion of the fuel.
During exhaust stroke, the exhaust valve remains opened
and inlet valve remains closed. Piston moves from BDC to
TDC. The products of combustion are swept out through
the exhaust valve.

16. Advantages :-
 High torque output
 Smooth running
 Lower emissions output
 Higher horse power availability
 Heavier construction
Disadvantages :-
 Heavy in weight
 More moving parts
 Exhaust smell
 Creates more pollution than petrol engine.

17. Comparison :-
Two Stroke Engines Four Stroke Engines
• The cycle of operation is completed
in two strokes.
• The cycle of operation is completed
in four strokes.
• Engines are lighter, compact and
require less space.
• Engine are heavier, larger and
require more space.
• Simple construction. • Complicated construction.
• High mechanical efficiency. • Low mechanical efficiency.
• Produce more noise. • Produce less noise.
• Moving parts are more. • Moving parts are less.
• Better balancing. • Balancing is a problem.
• Gives low vibrations. • Gives more vibrations.
• Compression ratio is low. • Compression ratio is more.