It is the most common type of the internal combustion engine and used in various automobiles like cars , trucks ,some motorcycles etc . It deliver one power stroke for every two cycles of the piston or four piston stroke. Four stroke engine has valves (inlet or exhaust) which is operated by the push rod ,cam , roker arms etc.
Four stroke engine complete two cycles in four strokes -:
1. Suction or intake stroke
2. Compression stroke
3. Power or expansion stroke
4. Exhaust stroke
1.Suction/ Intake stroke -: In this stroke piston move downward to the bottom, this increase the volume , inlet valve open and allow a air -fue mixture to enter into the chamber. In this process inlet valve open and exhaust valve close. Now half cycle is complete.
2.Compression stroke -: In compression stroke inlet valve close and the piston move upward or top dead centre. Due to movement of piston upward intake fuel mixture compress . And at the the end of this strokea spark plug is present to ignition. At this stage one cycle is complete .
3.Power stroke -: In the power stroke the compressed air-fuel mixture is ignited by the spark plug and combustion is start. Due to burning of fuel very high pressure gases produced which oppose the piston at the top face and now piston move downward and create the power output. Now one and half cycle is completed. In this stroke both valves are closed .
4. Exhaust stroke -: At the end of compression stroke the brunt gases is remain into the chember and which pushes the piston top side . At this time of syroke exhaust valve open and due to upward motion of piston waste gases is expelled outsude from the chamber through the exhaust valve. At the end of this stroke two complete cycles of four stroke engine is complete.
Again piston move downward and allow to enter fuel into the chember process will again start and cycle begins again.
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