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reciprocating engine[ri′sip·rə‚kād·iŋ ′en·jən]
a device in which a piston performs the basic function of transforming the energy of a working fluid. As the piston moves within a cylinder, there is a change in the volume of the chamber formed; as this occurs, various parameters of the working fluid, such as pressure and temperature, also change. During operation of a reciprocating engine, the energy of the working fluid may be decreased, as in a gasoline engine, or increased, as in a pump or compressor. The intake and exhaust of the working fluid in the cylinder are regulated by a distribution or timing mechanism using simple valves or slide valves or by the piston itself, as in a two-cycle engine.
The reciprocating engine is characterized by cyclic reoccurrence and intermittence of operation. In most reciprocating engines the piston is connected with the crankshaft by a crank gear, by means of which the reciprocating motion of the piston is converted into the rotary motion of the shaft, or vice versa. Because of the cyclic reoccurrence of operation and the presence of a crank gear, reciprocating engines do not operate at speeds as high as those achieved by rotodynamic machines; the former have a greater specific mass and greater factional losses. Reciprocating engines without connecting rods are now being used, in which reciprocating motion is converted to rotary motion by a powered mechanism without connecting rods. Rotary-piston engines, such as the Wankel engine, are also being used. In a steam pump, the reciprocating motion of the piston of a reciprocating engine is used directly to drive the pump’s piston; in a motor-driven compressor, the engine and compressor are combined in a single multicylinder unit. The use of a plunger as a piston in reciprocating engines makes it possible to operate pumps at higher pressures. Reciprocating engines are simple to operate, economical, reliable, and have a long operating life.
N. F. KAIDASH