The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into rotating motion.
All parts rotate consistently in one direction, as opposed to the common reciprocating piston engine, which has pistons instantly and rapidly changing direction 180 degrees. In contrast to the more common reciprocating piston designs, the Wankel engine delivers advantages of simplicity, smoothness, compactness, high revolutions per minute, and a high power-to-weight ratio. This is primarily because there are three power pulses per rotor revolution. In a two-stroke piston engine there is one power pulse per crankshaft revolution, with one in two revolutions in a four-stroke piston engine. Although at the actual output shaft of a rotary engine, there is only one power pulse per revolution, since the output shaft spins three times as fast as the actual rotor, as can be seen in the animation below, it makes it roughly equivalent to a two-stroke piston engine of the same displacement. This is also why the displacement only measures one face of the rotor, since only one face is working for each output shaft revolution.