A two-stroke diesel engine is a diesel engine that uses compression ignition in a two-stroke combustion cycle. It was invented by Hugo Güldner in 1899.
In compression ignition, air is first compressed and heated; fuel is then injected into the cylinder, causing it to self-ignite. This delivers a power stroke each time the piston rises and falls, without any need for the additional exhaust and induction strokes of the four-stroke cycle.