Diesel engines

Diagram of a 2-stroke diesel engine. Note the lack of spark plugs.

Large diesel engines in the engineroom of the Stena Hollandica.

Diesel engines are piston-powered internal combustion engines.

They differ from engines fueled by gasoline in that combustion in diesel engines occurs at a higher compression. Gasoline powered engines require a spark plug. The fuel used in diesel engines combusts spontaneously, due to the higher compression. This higher heat makes the engines more efficient, and allows them to use a wider range of fuel. Gasoline is inherently more expensive than the fuels used in diesel engines, because gasoline contains a higher fraction of lighter more volatile elements, like methane, butane, propane, which have their own specialized uses.

Some large diesel engines, like those used in marine vessels, are fueled by lower priced bunker fuel oil, which is preheated prior to being injected into the incoming air.

Some automobiles use diesel engines that have been modified to filter and re-use oil used to fry food.