1. INTERNAL COMBUSTION
ENGINE

2. What is an I.C. Engine?
An internal combustion engine (ICE) is a heat engine in which
the combustion of a fuel occurs with an oxidizer (usually air) in
a combustion chamber that is an integral part of the working
fluid flow circuit.

3. WORKING PRINCIPLES OF IC ENGINES
FOUR STROKE ENGINES :
Four Stroke Spark Ignition (SI) Engine
Four Stroke Compression Ignition (CI) Engine
TWO STROKE ENGINES:
Two Stroke SI Engines
Two Stroke CI Engines
SPARK IGNITION (SI) ENGINES
Spark Is Generated Through An External Source
COMPRESSION IGNITION (CI) ENGINES
Air is heated to a sufficiently high temperature because of high
compression ratio and the fuel gets self-ignited on injection as finely
atomized spray.

4. 4 STROKE SI ENGINE
• In four stroke engine the cycle of operation is completed in 4 strokes of piston or 2 revolutions
of crankshaft.
• During four strokes five events to be completed
1. Suction
2. Compression
3. Combustion
4. Expansion
5. Exhaust
• Each stroke consists of 180° of crank shaft rotation. Hence four stroke cycle is completed
through 720° of crank shaft rotation.
• Ideal four stroke engine consists of following 4 strokes-
1. Suction or Intake stroke
2. Compression stroke
3. Expansion or power stroke
4. Exhaust stroke

5. WORKING PRINCIPLE OF 4 STROKE SI ENGINE

6. 4 STROKE CI ENGINE
• The four stroke CI engine is similar to four stroke SI engine, but operates at high compression
ratio.
• The compression ratio of SI engine varies from 6 to 10, while the compression ratio of CI
engine varies from 16 to 22.
• In the CI engine during suction stroke air instead of fuel air mixture is inducted.
• The spark plug of SI engine is replaced with fuel injector.
• The sequence in a 4-stroke CI engine (Diesel engine) are:
1. Suction or Intake stroke
2. Compression stroke
3. Expansion or power stroke
4. Exhaust stroke

7. WORKING PRINCIPLE OF 4 STROKE CI ENGINE

8. 2 STROKE SI ENGINE
• In this 2 stroke SI engine the cycle Is completed In one revolution of the Crank
Shaft or in two stroke of the piston.
• The main difference between 2-stroke and 4-stroke engine is in themethod of
filling the fresh charge and removing burnt gases from the cylinder.
• In the 4 stroke engine these operations are performed by the pistonduring the
suction and exhaust strokes respectively.
• In a 2 stroke, the filling process is accomplished by the charge compressed in
the crank case. The induction of the compressed charge moves out the product
of combustion through exhaust ports. Therefore, no piston strokes are required
for these two operations.
• Two strokes are sufficient to complete the cycle, one for compressing the fresh
charge and the other for expansion or power stroke.

9. WORKING PRINCIPLE OF 2 STROKE SI ENGINE

10. 2 STROKE CI ENGINE
• More advantageous than 2 Stroke SI Engine.
• No loss of fuel with exhaust gases as he intake charge is only air.
• Hence many of the high output diesel engines work on this cycle.
• A general disadvantage common to both two stroke SI and CI
(diesel engines) is greater cooling and lubricating oil requirements
due to one power stroke per crank shaft rotation and higher
temperatures.
• Results in higher consumption of lubricating oil.

11. WORKING PRINCIPLE OF 2 STROKE CI ENGINE

12. ADVANTAGES OF SI ENGINES OVER CI
ENGINES
• Initial cost is less
• For a given output it is lighter in weight and occupies less
• space
• Due to low compression it is easy to start
• Flotation of speed is minimum and thus requires light flywheel

13. LIMITATIONS OF SI ENGINES
• Requires costly fuels and maintenance cost is high
• Chances of pre ignition of charge are more
• Less dependable
• Suitable only for light duty vehicles

14. SOME POINTS OF COMPARISON BETWEEN 2
STOKE AND 4 STROKE ENGINES

15. THANK YOU