A pistonless rotary engine is an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...

that does not use pistons in the way a

reciprocating engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common fea ...

does. Designs vary widely but typically involve one or more

rotor Rotor may refer to: Science and technology Engineering * Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element so called the stator *Helicopter rotor, the rotary wing(s) of a rotorcraft ...

s, sometimes called rotary pistons. Although many different designs have been constructed, only the

Wankel engine The Wankel engine (, ) is a type of internal combustion engine using an eccentric rotary design to convert pressure into rotating motion. It was invented by German engineer Felix Wankel, and designed by German engineer Hanns-Dieter Paschke. ...

has achieved widespread adoption. The term rotary combustion engine has been used as a name for these engines to distinguish them from early (generally up to the early 1920s) aircraft engines and

motorcycle engine A motorcycle engine is an engine that powers a motorcycle. Motorcycle engines are typically two-stroke or four-stroke internal combustion engines, but other engine types, such as Wankels and electric motors, have been used. Although some moped ...

s also known as ''

rotary engine The rotary engine is an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. The engine's crankshaft remained stationary in operation, while the entire crankcase and its ...

s''. However, both continue to be called ''rotary engines'' and only the context determines which type is meant, whereas the "pistonless" prefix is less ambiguous.

Pistonless rotary engines

A pistonless rotary engine replaces the linear reciprocating motion of a piston with more complex compression/expansion motions with the objective of improving some aspect of the engine's operation, such as: higher efficiency

thermodynamic cycles A thermodynamic cycle consists of a linked sequence of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and other state variables within the system, and that eventual ...

, lower

mechanical stress In continuum mechanics, stress is a physical quantity. It is a quantity that describes the magnitude of forces that cause deformation. Stress is defined as ''force per unit area''. When an object is pulled apart by a force it will cause elonga ...

, lower vibration, higher

compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression * Gas compression *Compression ratio, of a ...

, or less mechanical complexity. the Wankel engine is the only successful pistonless rotary engine, but many similar concepts have been proposed and are under various stages of development. Examples of rotary engines include: ;Production stage *

* LiquidPiston engine * Beauchamp Tower's nineteenth centur
spherical steam engine
(in actual use as a steam engine, but theoretically adaptable to use internal combustion) ;Development stage * Engineair engine * Hamilton Walker engine * Libralato rotary

Atkinson cycle The Atkinson-cycle engine is a type of internal combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power density. A variation of this approach is used in some modern auto ...

engine *

Quasiturbine The Quasiturbine or Qurbine engine is a proposed pistonless rotary engine using a rhomboidal rotor whose sides are hinged at the vertices. The volume enclosed between the sides of the rotor and the rotor casing provide compression and expansion i ...

* RKM engine, german: RotationsKolbenMaschine * Sarich orbital engine *

Trochilic engine A swing-piston engine is a type of internal combustion engine in which the pistons move in a circular motion inside a ring-shaped "cylinder", moving closer and further from each other to provide compression and expansion. Generally two sets of pis ...

* Wave disk engine * Nutating disc engine ;Conceptual stage *

Gerotor A gerotor is a positive displacement pump. The name ''gerotor'' is derived from "generated rotor". A gerotor unit consists of an inner and outer rotor. The inner rotor has ''n'' teeth, while the outer rotor has ''n''+1 teeth; with ''n'' defined a ...

engine * Integrated Supersonic Component Engine

Pistonless rotary engines

See also

Further reading