Four stroke engine, Difference Between Four Stroke and two Stroke Engine.

4-STROKE ENGINE
A four stroke engine delivers one power stroke for every two cycle of the piston, it utilize four distinct piston stroke to complete one operating cycle .The piston make two complete passes in the cylinder to complete one operating cycle.
STROKE
The movement of the piston from TDC to  BDC is called stroke 
4 cycles of the engine -

1. Intake
2. Compression
3. Power 
4. Exhaust

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1.Intake(Suction)

Air-fuel mixture is introduced to fill the combustion chamber. Intake take place when the piston moves from TDC(top dead center) to BDC(bottom dead center).

•  Intake valve is open
•  Exhaust valve is closed.

 2.Compression

 When the filled air-fuel mixture is compressed inside the cylinder . the compression chamber is sealed from the charge, and its ready for ignition.Piston move from BDC to TDC

• Intake valve is closed
• Exhaust valve is closed

3.Power
This stroke begin with the expansion of air-fuel mixture ignition with the help of spark plug. It is an engine operating stroke in which hot expending gases force the piston head away from the cylinder, this force is transferred to connecting rod to apply torque on the shaft.

• Intake valve is closed
• Exhaust valve is closed

4.Exhaust

In this stroke , the exhaust stroke is the final stroke and take place when the exhaust valve is open and the intake valve is closed. piston movement evacuated gases to the atmosphere .

• Intake valve is closed
• Exhaust valve is open

Difference between 4-Stroke and 2-Stroke Engine

Sl.no.	4-Stroke engine	2-Stroke engine
1.	One power stroke in every two revolution of crank shaft.	One power stroke in each revolution of crank shaft.
2.	Volumetric efficiency is more due to greater time if induction.	Volumetric efficiency less due to lesser time of friction.
3.	Heavier flywheel due to non-uniform turning movement.	Lighter flywheel due to more uniform turning movement.
4.	Thermal efficiency is high.	Thermal efficiency is less.
5.	Complicated valve mechanism, heavy weight	Valve mechanism and light weight.
6.	Used where high efficiency is important. e.g. automobile, power generation, aeroplane etc.	Used for light weight, low cost and efficiency is not big issue. e.g. scooter, bike..etc.
8.	Lesser cooling and lubricating requirement.	Greater cooling and lubricating requirement.
9	High initial cost.	Low initial cost.
10	More moving part.	Less moving part.

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