The engine design was created by another German Engineer by the name of Felix Wankel. The first working prototype of the engine was completed in 1957. While the Wankel (some may know it by the incorrect slang term “rotary”) design is based upon the same 4 cycles it achieves this by a completely different means.
Instead of having reciprocating pistons that move up and down inside a cylinder the Wankel design uses an eccentric rotary design to achieve the same 4 strokes. Below is a visual that demonstrates the design.
The most popular use of this type of engine in automotive use has been in the form of a well known Japanese sports car. The Mazda RX7 is responsible largely for the notoriety of this type of engine.The engines have been used in motorcycles built by Yamaha, Suzuki, and BSA and has been used aircraft as well, but in the minds of many a gear head, when you hear the word Wankel (or “Rotary Engine”) the term summons the picture of an RX7. Driving a vehicle equipped with a Wankel engine has been described by many as being more similar to riding a motorcycle than driving a car. This can be largely attributed to the much higher speeds that the engine is capable of. While most automotive engines have a speed limited to around 5,000-6,000 RPMs and make their best power around the mid range of that speed, Wankel engines are routinely capable of 7,000-8,000 RPMs and their power curve is very linear making the higher engine speeds much more usable.
The major difference in the designs of this and the Otto Cycle engine is that while the Otto needs two complete rotations of the crankshaft to have on power stroke (1/2 power stroke per revolution) the Wankel engine has one power stroke per revolution.
For more information on the Wankel design follow the links by clicking on the highlighted and underlined phrases in the article above.