Working concept of a four stroke engine

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A four-stroke engine comprises four distinct piston strokes - intake, compression, power, and exhaust - to complete an operating cycle. The engine requires two revolutions (720°) of the crankshaft. During the intake stroke, the air-fuel mixture is introduced into the combustion chamber as the piston moves from TDC to BDC with the intake valve open. Compression follows, where the charge is compressed and heated within the combustion chamber. The ignition event occurs when the charge is ignited, releasing heat energy through rapid oxidation. The power stroke involves hot expanding gases pushing the piston away from the cylinder head, transferring force to the connecting rod and crankshaft. Finally, the exhaust stroke expels spent gases through the open exhaust valve as the piston moves back to TDC, completing an operating cycle. Four-stroke engines are widely used in small engines due to their efficiency.