Power stroke (engine)

Reciprocating motion, used in reciprocating engines and other mechanisms, is back-and-forth motion. Each cycle of reciprocation consists of two opposite motions: there is a motion in one direction, and then a motion back in the opposite direction. Each of these is called a stroke. The term is also used to mean the length of the stroke.

In a steam locomotive, or in a steam, Otto, Diesel or piston engine, a stroke is the action of a piston travelling the full length of its locomotive cylinder or engine cylinder in one direction.

The stroke length is determined by the cranks on the crankshaft. Stroke can also refer to the distance the piston travels. Engine displacement is dependent on both the diameter of the cylinder, known as its bore, and the stroke of the Piston.

In a pistonless rotary engine, the term is applied to the corresponding rotor movement; see Dead centre.

Most modern internal combustion engines work on a four-stroke cycle; that is, a complete cylinder cycle consists of four discrete strokes, as described below. Other types of engines can have very different stroke cycles.

The induction stroke is the first stroke in a four-stroke internal combustion engine cycle. It involves the downward movement of the piston, creating a partial vacuum that draws (allows atmospheric pressure to push) a fuel/air mixture into the combustion chamber.

In a reciprocating engine, it is that portion of the cycle when the pistons move from TDC (top dead center) to BDC (bottom dead center) and the fuel-air mixture is drawn into the cylinders....

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