Rotary Engine

A rotary engine, more precisely called a Wankel rotary engine after its inventor Felix Wankel, replaces the pistons and cylinders of a conventional engine with a triangular rotor spinning inside an epitrochoid-shaped (oval-like) housing. As the rotor turns, the three points of the triangle trace the housing's inner wall, and the space between each point and the wall continuously expands and contracts, creating the same intake, compression, combustion, and exhaust phases as a piston engine, but through pure rotation. This eliminates the reciprocating mass of pistons and connecting rods, letting rotary engines rev higher and run smoother than similarly sized piston engines.

Mazda is the manufacturer most associated with the rotary engine, having refined the design across decades of production in cars including the RX-7, RX-8, and earlier RX-3 and Cosmo models, as well as the Le Mans-winning 787B race car. Rotary engines are compact and lightweight relative to their power output and are known for a distinctive high-pitched exhaust note and eagerness to rev well past the redline of a comparable piston engine. Because the design produces less torque per unit of displacement than a piston engine, rotary-powered cars are typically built light and geared to exploit the engine's high-RPM power delivery.

The rotary engine's chief mechanical vulnerability is its apex seals, the components at each tip of the rotor that maintain the seal against the housing wall. These seals wear faster than piston rings under sustained high RPM or poor maintenance, leading to compression loss, and rotary engines also consume oil by design since a small amount is metered into the combustion chamber to lubricate the seals. Mazda ended series production of the rotary in the RX-8 in 2012, though it has since reintroduced a rotary engine as a range extender in later hybrid concept and production vehicles.