What are the variants of the internal combustion engine?

Any engine in which combustion happens in internally is a variant of the internal combustion engine

The Wankel rotary engine, jet engines, rocket engines are a few of the well used variants

Mainly they are:
1. Continuous combustion Engine. Thrust type. Example: Turbo Engine
2. Intermittent combustion Engine. Cylinder Piston and Stroke Type. Example: Piston Engine 4stroke/ 2stroke.
3. Wankel Engine. (Roatary with Internal Combustion per cycle)
4. Rotary Engine. Torque Type. (Rotor With Vanes or Piston type Tight cross section).
5. Soild Rocket Engine with uncontrolled combustion.
6. Controlled combustion Engine. Example: Liquid fuel.
7. With Ignition. Petrol Engines.
8. With compression Ignition.
9. Depending on components used.
10. Depending on strokes/ processes used.
11. Depending on Fuel used.
12. Depending on Environment used.Air Water Road Space.