The rotary engine (originally conceived and developed by Dr. Felix Wankel) is sometimes called a Wankel engine, or Wankel rotary engine. In this design, instead of pistons bouncing up and down a rotor follows a path that looks like something you’d create with a Spirograph. This path keeps each of the three peaks of the rotor (corners of the triangle looking thing) in contact with the housing (the case surrounding the rotor), creating three separate pockets. As the rotor moves around the chamber, each of the three pockets changes shape, and therefore size, alternatively getting bigger or smaller. It’s this change in size that draws air and fuel into the engine, squeezes it, makes useful power as the gases expand (by exploding them!) and then pushes out the exhaust.
Like any combustion engine, a rotary needs air, fuel, and compression (to squeeze the air & fuel, heating it up) Gasoline engines need a spark to ignite the air and fuel, but diesel engines just squeeze the fuel harder until it ignites.
As the intake port is exposed by the motion of the rotor, the volume of space between the rotor and the housing expands. This draws in the air/fuel mix without the use of valves (neat, huh?). In a carbureted system the air is drawn first through the carburetor, mixing with atomized gasoline, then into the engine. In a fuel injection system the injectors squirt a stream of atomized fuel into the intake manifold where it mixes with the air rushing past on its way into the engine.
The motion of the rotor seals in the air/fuel mix between one rotor face and the rotor housing in a rapidly shrinking pocket. This squeezes the mix, increasing pressure and temperature.
With the air/fuel mix compressed into a small, hot space the spark plug fires and ignites an explosion. The force of the resulting boom pushes against the rotor face, creating the spinning motion that actually turns the engine and makes your car go!
The rotor continues on its path and the space filled with the smoke from the explosion reaches an exhaust port. The space gets smaller again, pushing the exhaust gasses out before continuing on its way to once more pass the intake port and start the cycle all over again.
More Bang For Your Buck
One of the many interesting things about a rotary engine is the 3-sided design of the rotor means there are 3 explosions to turn the rotor just once. A piston engine, in contrast, has only one explosion for every two times the piston goes up and down. This three-bang -per-turn results in the rotary design generating a lot of power for an otherwise very small engine.
The rotor itself has three convex faces, each of which acts like a piston. Each face of the rotor has a pocket in it, which increases the displacement of the engine (the amount of air and fuel the engine can burn in one explosion, creating more power).
At each apex (the three corners of the triangle) is a metal blade that forms a seal to the outside of the combustion chamber. There are also metal rings on each side of the rotor that seal to the sides of the combustion chamber.
The rotor has a set of internal gear teeth cut into the center of one side. These teeth mate with a gear that is fixed to the housing. This gear mating determines the path and direction the rotor takes through the housing.