• A four stroke engine is an internal combustion engine in which the piston completes four separate strokes while turning the crank shaft.
• A four stroke engine delivers one power stroke for every two cycles of the piston.
• Following strokes are continuously taking place.
ü Suction stroke – Suction of air fuel mixture takes place.
ü Compression stroke – Adiabatic compression of air fuel mixture.
ü Power stroke – Combustion and adiabatic expansion taking place.
ü Exhaust stroke – Burnt gases are exhausted from the cylinder.
SUCTION STROKE :-
• During suction stroke, inlet valve is opened and exhaust valve is closed.
• Piston moves TDC to BDC
• When the piston moved TDC to BDC vacuum is created inside the cylinder.
• Due to the vacuum air fuel mixtures is drawn into the cylinder.
• Inlet valve is closed at the end of suction stroke.
COMPRESSION STROKE :-
• In compression stroke piston moves from BDC to TDC.
• Air fuel mixture is compressed by the movement of piston (Upward direction).
• Both valves are closed in this stroke.
• Now the volume of air fuel mixture is reduced and pressure of the gas is increased.
• At the end of compression stroke air fuel mixture is ignited by the spark plug.
• Now burning of the air fuel mixture takes place.
POWER OR EXPANSION STROKE:-
• Due to the combustion, high pressure and temperature are developed inside the engine.
• At this time two valves are closed.
• Now piston moves TDC to BDC by this pressure. Due to this movement crank shaft is rotated.
• Here, reciprocating motion of the piston is converted into the rotary motion.
• So that Power will be created in this stroke.
EXHAUST STROKE:-
• In this stoke piston moves BDC to TDC.
• At this time inlet remains is closed and exhaust valve opens.
• Now burnt gases are goes to the atmosphere through exhaust valve.
• At the end of exhaust stroke exhaust stroke will be closed and inlet valve will be opened.
• Now suction stroke will start.
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