The Otto Cycle

Diesel engines, like gasoline engines, have cylinders and pistons and burn a liquid fuel. They may use either a two- or four-stroke cycle. Diesel engines' main difference from gasoline engines is that there is no electrical spark to ignite the fuel. Ignition occurs spontaneously when the air-fuel mixture reaches the right temperature and pressure.

Two-stroke engines only require two strokes to complete the combustion cycle. They are commonly found in lower-power applications such as lawn and garden equipment and smaller motorcycles.