rotary engine

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rotary engine,

internal-combustion engine whose cycle is similar to that of a piston engine, but which produces rotary motion directly without any conversion from reciprocating motion. A major problem associated with engines of this type is preventing the leakage of combustion gases. The only type of rotary engine currently considered to be of practical value is the Wankel engine (see internal-combustion engineinternal-combustion engine,
one in which combustion of the fuel takes place in a confined space, producing expanding gases that are used directly to provide mechanical power.
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). Although the gas turbine produces rotary motion directly, it is not generally considered a rotary engine because it functions differently.

Rotary Engine


an internal-combustion engine in which the energy of the combustion gases is converted into mechanical energy by means of a rotor that undergoes rotary or rotary-reciprocating motion relative to the body of the engine. The concept of the rotary engine, also called the rotary-piston engine, was first proposed in the 16th century, and several thousand patents for rotary engines have been registered. The first attempt to construct a working model of a rotary engine was in 1799, but the first practical rotary engine—the Wankel engine—only appeared in 1957.

In operation, the combustion chamber is formed by the surfaces of a rotor and the chamber walls; the volume of the chamber varies in a periodic manner as the cycles of compression and expansion of the working fluid are continuously repeated. Thus, rotary engines can have the same two-stroke and four-stroke operations characteristic of internal-combustion piston engines.

Modern rotary engines are produced with one, two, or three working sections—that is, one, two or three rotors, respectively, are located on a common eccentric shaft.


Khanin, N. S., and S. B. Chistozvonov. Avtomobil’nye rotorno-porshnevye dvigateli. Moscow, 1964.
Mototsikl: Teoriia, konstruktsiia, raschet. Moscow, 1971.


rotary engine

[′rōd·ə·rē ′en·jən]
(mechanical engineering)
A positive displacement engine (such as a steam or internal combustion type) in which the thermodynamic cycle is carried out in a mechanism that is entirely rotary and without the more customary structural elements of a reciprocating piston, connecting rods, and crankshaft.

Rotary engine

Internal combustion engine that duplicates in some fashion the intermittent cycle of the piston engine, consisting of the intake-compression-power-exhaust cycle, wherein the form of the power output is directly rotational.

Four general categories of rotary engines can be considered: (1) cat-and-mouse (or scissor) engines, which are analogs of the reciprocating piston engine, except that the pistons travel in a circular path; (2) eccentric-rotor engines, wherein motion is imparted to a shaft by a principal rotating part, or rotor, that is eccentric to the shaft; (3) multiple-rotor engines, which are based on simple rotary motion of two or more rotors; and (4) revolving-block engines, which combine reciprocating piston and rotary motion. See Automobile, Combustion chamber, Diesel engine, Gas turbine, Internal combustion engine, Otto cycle

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