Four-stroke engine

An internal-combustion engine that completes a cycle in four piston strokes: intake, compression, power, and exhaust. Its crankshaft turns twice per cycle.

Intake stroke: The piston’s downward movement that draws an air–fuel mixture, or air alone, into a cylinder. This first stroke fills the cylinder before compression begins.
Piston: A moving component that forms one wall of an engine’s combustion chamber and transmits gas pressure to a connecting rod. Its reciprocation defines the four strokes.
Two-stroke engine: An internal-combustion engine that completes its cycle in two piston strokes, usually combining intake and exhaust with other phases. It completes a cycle in half as many piston strokes.
Automobile engine: An engine designed to propel a passenger or commercial road vehicle. Most modern car engines use four-stroke cycles.
Nikolaus Otto: A German engineer associated with the successful development of the four-stroke internal-combustion engine. His 1876 engine made the four-stroke cycle practical.
Compression stroke: The piston’s upward movement that compresses the cylinder’s charge before combustion. Compression prepares the charge for ignition at the cycle’s turning point.
Cylinder: A chamber in which an engine piston moves and combustion pressure is generated. The cycle’s charge is drawn into, compressed within, and expelled from it.
Diesel engine: An internal-combustion engine that ignites fuel by injecting it into hot, compressed air. Many diesel engines use four strokes but ignite fuel without a spark plug.
Motorcycle engine: An engine that supplies propulsion for a motorcycle. Four-stroke designs are common in motorcycles, especially larger models.
Beau de Rochas cycle: A four-phase engine cycle described by Alphonse Beau de Rochas in 1862. It set out the principles later embodied in Otto’s working engine.

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