The primary difference between internal and external combustion engines lies in where the power is developed. In an internal combustion engine fuel is ignited and burned inside the same container where the power is developed while in an external combustion engine the fuel is ignited outside the engine and the resulting power sent to it.

Combustion is the burning of an air-fuel mixture to provide energy. It requires the presence of air, fuel, and a heat source to ignite the air-fuel mixture. In the internal combustion engine that powers automobiles and trucks the combustion happens inside the engine utilzing a fuel like gasoline, diesel fuel, or natural gas.

The catalytic converter converts pollutants in exhaust gas into less pollutant substances like carbon dioxide and water.

Spark plugs receive current from the distributor and use it to spark combustion in the combustion chamber of a cylinder.

The crankshaft converts the reciprocating motion of the piston into the rotational motion that's used to power the vehicle and its components.