The inlet port is uncovered and fuel-air mixture enters the working chamber. The lobe of the rotor covers the inlet port, and the rotor moves the mixture around the chamber.
The rotor turns. The working chamber becomes smaller, compressing the mixture.
It is smallest at the top of the compression phase. And that is when the air-fuel mixture is ignited. Hot, expanding gases apply force to the rotor and produce a power pulse which turns the rotor. This power impulse is also called Expansion.
The apex of the rotor uncovers the exhaust port, and exhaust gases are pushed out of the chamber.
This completes one cycle. In rotary engines, the stages are called phases. So one engine cycle has four phases.
