1.intake stroke:in this stroke,vapours of petrol mixed with air are admitted into a cylinder through the intake valve.this happens when the air pressure inside the cylinder decrease due to downward motion of the piston.the mixing of air and petrol takes place in carburetor.
2.compression stroke:at the end of intake stroke the intake valve closes and the piston starts moving up.The petrol-air mixture is compressed by the upward moving piston which heats the mixture.In high compression engines,the mixture is compressed to 1/8th of its initial volume.the efficiency of engine increases with increase in compression.
3.power stroke:After the compression stroke as the piston starts moving down due to momentum,fuel in the mixture is ignited by a spark produced by a spark plug.The temperature becomes high.The pressure increases to about 25 atmospheres.Due to high temperature and pressure,themixture expands pushing the piston down and in the process it does work.The temperature of the mixture falls during expansion
4.Exhaust stroke:The exhaust valves opens up when the piston starts moving upward.Simultaneously,the spent gases are thrown out.The above four operations make one cycle of the heat engine.The cycle is repeated at rapid rate.The to and fro motion of piston is converted into rotational motion of wheels by the use of piston rod and crank
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