Most cars you see on the road have a traditional piston engine under the hood. However, a few models may offer a distinct difference with a pistonless rotary engine or rotor engine. Instead of pistons, they have rotors.
Fewer parts that move
A rotor engine doesn’t have as many moving components as you see with the piston engine. Just think of all of the components on a piston engine. You have the connecting rods, camshaft, valves, rockers, timing belt, timing gears, crankshaft and of course, the pistons. Even the simplest engine will have at least 40 parts.
A rotary engine has just three moving parts with the two-rotor engine. Two of them are the rotors with the third being the output shaft. Because of the fewer moving parts, there is greater reliability from the engine.
Parts in a traditional piston engine change directions as they rotate, while those in a rotary engine move in the same direction. They also feature counterweights that eliminate vibrations which occur in piston engines.
The rotor engine is also smoother than a piston one. It has three revolutions on the output shaft for one revolution of the rotor. For the piston engine, the combustion happens on every two revolutions and a quarter of each crankshaft revolution. The rotors on the rotary engine move slower than on a piston engine, which improves reliability.
Rotary engines are not seen in many vehicles, especially those in the U.S. because of emissions. However, Mazda has had a great deal of success with the Wankel engine, which is a type of rotary engine, used with racing cars.