A combustion engine is a type of engine that converts fuel into mechanical energy through a process called combustion. In this process, fuel, such as gasoline or diesel, is mixed with air and ignited, creating a series of small explosions. These explosions push pistons, which then turn the crankshaft to produce motion, powering vehicles like cars and trucks. There are two main types of combustion engines: internal combustion engines and external combustion engines. Internal combustion engines burn fuel inside the engine itself, while external combustion engines burn fuel outside the engine to produce steam or hot gases that drive the engine.