The wankel engine uses a curved triangle within an almost "8-shaped" chamber to create chambers of compression. The internal shaft (A, see animation on the right) rotates three times to every one cycle of the rotor (B, refer to animation).
These engines do not require valves, because the intake and exhaust chambers are always open. Although they are mechanically simple, these engines are rarely mass-produced due to reliability issues that can result from poor geometrical engineering. Currently, the only auto manufacturer to mass-produce this engine is Mazda, in models such as the RX-7 and RX-8. The engine has found its way into other applications, often due to its impressive power-to-weight ratio.
Apex seals are similar to piston rings in that they seal off the edge of the rotor to retain combustion pressure. There are three of them per rotor; one at each tip.
What are Apex Seals Made of?
Apex seals are typically made out of high carbon steel, but the Mazda 787B race car used ceramic apex seals.
How a Rotary Engine Works Video
Rotary Rotation Demonstration
Images courtesy of Wikimedia Commons.