structural:summarization
A pistonless rotary engine is an internal combustion engine that does not use pistons in the way a reciprocating engine does. Designs vary widely but typically involve one or more rotors, sometimes called rotary pistons. Although many different designs have been constructed, only the Wankel engine has achieved widespread adoption. The term rotary combustion engine has been used as a name for these engines to distinguish them from early 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, whereas the "pistonless" prefix is less ambiguous.