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Internal-Combustion Engine is any type of machine that obtains mechanical energy directly from the expenditure of the chemical energy of fuel burned in a combustion chamber that is an integral part of the engine. Four principal types of internal-combustion engines are in general use: the petrol engine, the diesel engine, the rotary engine, and the gas turbine. The Diesel engine operates on a different principle and usually uses oil as a fuel. It is employed …

…or sleeve valves. The valves are normally held closed by the pressure of springs and are opened at the proper time during the operating cycle by cams on a rotating camshaft that is geared to the crankshaft (see CAM). By the 1980s more sophisticated fuel-injection systems, also used in diesel engines, had largely replaced this traditional method of supplying the proper mix of air and fuel; computer-controlled monitoring systems improved fuel economy and reduced pollution.