The document discusses alternatives to internal combustion engines, including the Wankel engine, gas turbine engine, and free piston engine. The Wankel engine uses a rotor inside an oval-shaped housing to generate power through rotary motion rather than pistons. A gas turbine engine compresses air, ignites fuel for combustion, and uses the expanding gases to power a turbine. A free piston engine uses the force of combustion to directly power a load without a crankshaft.