A pistonless rotary engine is an internal combustion engine that does not use reciprocating pistons in the way a reciprocating engine does, but it still relies on the same distinct induction, compression, ignition, exhaust phases and the same enclosed volumes and gas pressure increase due to combustion to generate power. Designs vary widely but typically involve one or more rotors, sometimes called rotary pistons, as described in QT-Wankel: Two Concepts 100 Years Apart. Although many different designs have been constructed, only the Wankel engine has achieved widespread adoption.