The Internal Combustion Engine

Heat engines come in two basic types: external-combustion and internal-combustion. Fuel for an external-combustion engine is burned outside the engine. Fuel for an internal-combustion engine is burned inside it.

Steam engines are external-combustion engines powered by steam produced outside the engine by using a fuel, such as coal, to boil water.

The internal-combustion engine is the most common type of engine used today. Typical automobile engines are internal-combustion engines, as are the engines in boats, lawn mowers, and home generators.

Internal-combustion engines may be either reciprocating or rotary. The reciprocating engine, with pistons that move back and forth, is the type used in most automobiles. In a rotary engine, such as a jet turbine, power is supplied directly to vanes or other rotating parts.