An internal combustion engine (ICE) is a thermal engine where the combustion of a fuel occurs with an oxidant (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of high temperature and high pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, rotor or a nozzle. This force moves the component at a distance, transforming chemical energy into useful mechanical energy.
The first commercially successful internal combustion engine was created by Étienne Lenoir around 1859 and the first modern internal combustion engine was created in 1876 by Nikolaus Otto (see Otto engine).
The term internal combustion engine generally refers to an engine in which combustion is intermittent, such as the most familiar four-stroke and two-stroke piston engines, along with variants, such as the six-stroke piston engine and the rotary engine Wankel. A second class of internal combustion engines uses continuous combustion: gas turbines, jet engines and most rocket engines, each of which are internal combustion engines following the same principle as described above. Firearms are also a form of internal combustion engine.
In contrast, in external combustion engines, such as steam engines or Stirling, energy is supplied to a fluid that is not composed, mixed or contaminated by combustion products. The working fluids can be air, hot water, pressurized water or even liquid sodium, heated in a boiler. ICEs usually work with high-energy fuels such as gasoline or diesel, fluids derived from fossil fuels. While there are many stationary applications, most ICEs are used in mobile applications and are the dominant power source for vehicles such as automobiles, airplanes and boats.
In general, an ICE is fueled by fossil fuels such as natural gas or petroleum products, such as gasoline, diesel fuel or fuel oil. There is an increasing use of renewable fuels such as biodiesel for compression ignition engines and bioethanol or methanol for spark ignition engines. Sometimes hydrogen is used, and it can be obtained from fossil fuels or renewable energy.
