How does the Four Stroke Engine Work

How four stroke engine work

Lets start with basic:-

what is an internal combustion engine

“It is a heat engine which produce motive power by burning of fuel like petrol, diesel, oxidizer etc. inside the chamber and generate torque which is used to move vehicle”.

Types of  internal combustion engine:-

1)Two stroke internal combustion engine

2)four stroke internal combustion engine

What is Two stroke internal combustion engine:-

It is a type of an internal combustion engine which complete its power cycle with two stroke (up and down movement) of the piston during only one crankshaft revolution.

how two stroke engine work



What is four stroke internal combustion engine:-

It is most commonly used I.C. engine in which piston complete four separate stroke(intake, compression, power and exhaust)

four stroke engine

Lets see How does four stroke engine work:-

In four stroke internal combustion engines the four events namely suction, compression, power and exhaust take place inside the engine cylinder. This four events are completed in two revolution of the crank shaft.Engine having two valve for controlling inlet and outlet of exhaust gases.This valves are controlled by cams, fitted on camshaft.This camshaft is driven by using crankshaft with the help of gears.This camshaft runs at half the speed of the crankshaft.


Following events are take place in I.C.engine :-

  • Suction stroke
  • Compression stroke
  • Power stroke
  • Exhaust stroke


Suction stroke

During suction stroke inlet valve opens and the piston moves in downward direction. Only  mixture of air and fuel are drawn inside the cylinder. During suction stroke exhaust valve remain closed and Pressure inside engine is less than atmospheric pressure.

four stroke engine intake stroke



Compression stroke

During this stroke the piston moves in upward direction. Both inlet valves and exhaust valve remain closed in this stroke. The charge air and fuel mixture taken in the cylinder is compressed by the upward movement of piston.

In diesel engine only air is compressed and diesel is injected at the end of compression stroke and ignition of fuel take place due to high pressure and temperature of the compressed air.

In case of petrol engine, air and fuel mixture is ignited by a spark plug.

four stroke engine compression stroke


Power stroke

After ignition of fuel, huge amount of heat and pressure is generated, This high  generated pressure in the engine cylinder pushes the piston downward . This instant downward movement of piston is called power stroke.The connecting rod  attached with piston transmits the power from piston to the crank shaft and crank shaft start rotating. Mechanical work can be taped at the rotating crank shaft. Both valves inlet and outlet remain closed during power stroke.

four stroke engine power stroke



Exhaust stroke

During Exhaust stroke piston moves in upward direction and Exhaust valve remain open during this stroke and all burnt exhaust gases go out through this valve.

After throwing all burnt gases out from engine,  again it ready to receive fresh charge.

We found that out of four stroke , there is only one power stroke and three idle strokes in four stroke cycle engine. The power stroke supplies necessary momentum for useful work.

four stroke engine exhaust stroke


Author :-

Gopinath Murthi


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