Pistonless rotary engine
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A pistonless rotary engine is an internal combustion engine that does not use pistons in the way a reciprocating engine does, but instead uses one or more rotors, sometimes called rotary pistons. An example of a pistonless rotary engine is the Wankel engine.
The term rotary combustion engine has been suggested[by whom?] as an alternative name for these engines to distinguish them from early (generally up to the early 1920s) aircraft engines and motorcycle engines also known as rotary engines. However, both continue to be called rotary engines and only the context determines which type is meant.
Pistonless rotary engines
The basic concept of a pistonless rotary engine avoids the reciprocating motion of the piston with its inherent vibration and rotational-speed-related mechanical stress. As of 2006[update] 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
- Beauchamp Tower's nineteenth century spherical steam engine (theoretically adaptable to use internal combustion)
- The Wankel engine
- Development stage
- The Baylin engine 
- The Engineair engine
- The Liquidpiston engine
- The Crankless engine 
- The Hamilton Walker engine
- The Libralato rotary Atkinson cycle engine
- The Quasiturbine
- The Ramgen Integrated Supersonic Component Engine
- The Rand cam engine
- The RKM engine, German: RotationsKolbenMaschine
- The Sarich orbital engine
- The Tri-Dyne Engine
- The Trochilic engine
- The Wave disk engine
- The Moto Turbine Radiale by Jean Claude Lefeuvre 
- The Jonova engine
- The Renault-Rambler lobular rotor engine (Spanish pat nº 0313466)
- Conceptual stage
- "How the Baylin Engine Works." Popular Mechanics, July 1946, pp. 131-132.
- "Tri-Dyne: Slick New Rotary Engine Could Lick the Wankel." Popular Science, July 1969, pp. 45-47 & 160-162.
- Jan P. Norbye: 'Rivals to the Wankel: A Roundup of Rotary Engines', Popular Science, Jan 1967, pp 80-85.