What is the name of the cycle used in most gasoline engines?

The cycle used in most gasoline engines is the Otto cycle. It is the idealized thermodynamic cycle for spark-ignition piston engines, the type commonly associated with gasoline or petrol-powered cars and motorcycles.

The ideal cycle models four main stages: isentropic compression, heat addition at approximately constant volume, isentropic expansion, and heat rejection at approximately constant volume. In a real four-stroke engine, these ideas correspond broadly to intake, compression, power, and exhaust strokes. A spark ignites the compressed air–fuel mixture near the end of compression, producing the expansion that drives the piston.

The cycle is named after German engineer Nicolaus Otto, whose practical four-stroke gas engine helped establish the design in the nineteenth century. Alphonse Beau de Rochas patented the four-stroke principle in 1861, before Otto built his successful engine. The main mix-up is with the Diesel cycle: diesel engines use compression ignition rather than a spark plug. The Carnot cycle is an ideal efficiency benchmark, while the Rankine cycle is commonly associated with steam power plants.