Any engine in which a fuel-air mixture is burned in the engine proper so that the hot gaseous products of combustion act directly on the surfaces of its moving parts, such as those of pistons (see piston and cylinder ) or turbine rotor blades.
Internal-combustion engines include diesel engines , gas turbine engines, pure jet engines , and {{link=rocket">rocket engines and motors, and are one class of heat engines. They are commonly divided into continuous-combustion engines and intermittent-combustion engines. In the first type (e.g., jet engines) fuel and air flow steadily into the engine, where a stable flame is maintained for continuous combustion. In the second (e.g., gasoline–reciprocating-piston engines), discrete quantities of fuel and air are periodically ignited. See also automobile industry, machine , steam engine .