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heat engine[′hēt ‚en·jən]
an engine in which thermal energy is converted into mechanical work. Heat engines, which make up the largest group among prime movers, use natural energy sources in the form of chemical or nuclear fuel.
The basis of operation of a heat engine is a closed or arbitrarily closed thermodynamic cycle. The operating efficiency of an ideal heat engine is determined by its thermal efficiency. The operation of a real heat engine, which has additional losses—for example, heat losses and losses caused by friction and vortex formation—is evaluated by the actual efficiency, which is the ratio of the mechanical work at the output shaft of the engine to the heat energy supplied. The actual efficiency of heat engines ranges from 0.1 to 0.6.
Heat engines are divided into piston, rotary, and jet heat engines according to the type of machine carrying out the working thermodynamic process. Combinations of these types, such as turbojet and Wankel engines, are possible. According to the means of heating the working body, heat engines are subdivided into internal-combustion engines, in which both the combustion of fuel and conversion of heat into mechanical work occur in the same working chambers of the engine (the cylinders), and external-combustion engines, in which the working body is obtained or heated outside the engine proper in special devices (for example, the Stirling engine and the steam engine).
O. N. EMIN