The internal combustion engine is an engine in which the combustion of fuel and an oxidizer (typically air) occurs in a confined space called a combustion chamber. This exothermic reaction creates gases at high temperature and pressure, which are permitted to expand. Internal combustion engines are defined by the useful work that is performed by the expanding hot gases acting directly to cause the movement of solid parts of the engine.Encyclopedia Britannica: Internal Combustion enginesAnswers.com Internal combustion engineColumbia encyclopedia: Internal combustion enginehttp://www.infoplease.com/ce6/sci/A0825332.html

The term Internal Combustion Engine (ICE) is often used to refer to an engine in which combustion is intermittent, such as a Wankel engine or a reciprocating piston engine in which there is controlled movement of pistons, cranks, cams, or rods.Donald Routledge Hill (1998). Studies in Medieval Islamic Technology II, (1st paragraph) p. 232 However, continuous combustion engines such as jet engines, most rockets, and many gas turbines are also classified as types of internal combustion engines. This contrasts with external combustion engines such as steam engines and Stirling engines that use a separate combustion chamber to heat a separate working fluid—which then in turn does work, for example, by moving a piston or a turbine.

A huge number of different designs for internal combustion engines exist, each with different strengths and weaknesses. Although they're used for many different purposes, internal combustion engines particularly see use in mobile applications such as cars, aircraft, and even handheld applications: all where their ability to use an energy-dense fuel (especially fossil fuels) to deliver a high power-to-weight ratio.

Applications

The motion of internal combustion engines is usually performed by the controlled movement of pistons, cranks, rods, rotors, or even the entire engine itself.

Internal combustion engines are most commonly used for mobile propulsion in vehicles and portable machinery. In mobile equipment, internal combustion is advantageous since it can provide high power-to-weight ratios together with excellent fuel energy density. Generally using fossil fuel (mainly petroleum), these engines have appeared in transport in almost all vehicles (automobiles, trucks, motorcycles, boats, and in a wide variety of aircraft and locomotives). This vehicles, when are not hybrid, are called All-Petroleum Internal Combustion Engine Vehicles (APICEVs) or All Fossil Fuel Internal Combustion Vehicles (AFFICEVs).