Editing Four-stroke engine (section)

===Diesel cycle===
{{Main|Diesel cycle}}
[[File:1 Audi R15.jpg|thumb|right|Audi Diesel R15 at Le Mans]]

The [[diesel engine]] is a technical refinement of the 1876 Otto-cycle engine. Where Otto had realized in 1861 that the efficiency of the engine could be increased by first compressing the fuel mixture prior to its ignition, [[Rudolf Diesel]] wanted to develop a more efficient type of engine that could run on much heavier fuel. The [[Etienne Lenoir|Lenoir]], Otto Atmospheric, and Otto Compression engines (both 1861 and 1876) were designed to run on [[Coal gas|Illuminating Gas (coal gas)]]. With the same motivation as Otto, Diesel wanted to create an engine that would give small industrial companies their own power source to enable them to compete against larger companies, and like Otto, to get away from the requirement to be tied to a municipal fuel supply.{{citation needed|date=June 2023}} Like Otto, it took more than a decade to produce the high-compression engine that could self-ignite fuel sprayed into the cylinder. Diesel used an air spray combined with fuel in his first engine.

During initial development, one of the engines burst, nearly killing Diesel. He persisted, and finally created a successful engine in 1893. The high-compression engine, which ignites its fuel by the heat of compression, is now called the diesel engine, whether a four-stroke or two-stroke design.

The four-stroke diesel engine has been used in the majority of heavy-duty applications for many decades. It uses a heavy fuel containing more energy and requiring less refinement to produce. The most efficient Otto-cycle engines run near 30% thermal efficiency.{{clarify|reason=Did some text about diesel thermal efficiency fall off?|date=October 2021}}