What type of engine uses a triangular rotor instead of pistons?

A Wankel engine uses a triangular rotary rotor instead of conventional reciprocating pistons.

The rotor has a curved triangular form related to a Reuleaux triangle and spins inside a figure-eight-shaped housing. Its three sides create three moving working chambers, where intake, compression, combustion, and exhaust occur as the rotor moves. An eccentric shaft converts the rotor’s motion into useful rotary output.

The design was developed from work by German engineer Felix Wankel, while Hanns-Dieter Paschke created the practical configuration used in production engines. Mazda became the best-known manufacturer of road-going Wankel cars, including the RX-7 and RX-8.

The Wankel layout is compact, smooth, and mechanically simple because it has fewer major moving parts than a piston engine. However, sealing, emissions, fuel economy, and heat management have limited its widespread use. The rotor is sometimes called a rotary piston, so saying it works with “no pistons” is a useful shortcut, not a claim that the engine has no piston-like working element.