For a description of an external-combustion engine, see Steam Engine.
Engine in which combustion of fuel takes place in a confined space, producing
expanding Gases (see States Of Matter) that are used to provide mechanical Power. The most common internal-combustion engine is the four-stroke reciprocating
engine used in automobiles. Here, mechanical power is supplied by a piston
fitting inside a cylinder. On a downstroke of the piston, the first stroke, fuel
that has been mixed with Air (by Fuel Injection or using a Carburetor) enters the cylinder through an
intake valve; the piston moves up to compress the mixture at the second stroke; at
ignition, the third stroke, a spark from a spark plug ignites the mixture,
forcing the piston down; in the exhaust stroke, an exhaust valve opens to vent the
burned gas as the piston moves up. A rod connects the piston to a crankshaft.
The reciprocating (up and down) movements of the piston rotate the crankshaft,
which is connected by gearing to the drive wheels of the automobile. The
ignition spark is provided by an electrical system whose power comes from a battery,
which also supplies power to the starting system, a small electric Motor that turns the crankshaft until the engine takes over. The engine is cooled
by Water circulating around the cylinders and is lubricated by motor Oil driven around the moving engine parts by an oil Pump. The two-stroke engine, which combines intake and compression in the first
stroke and power and exhaust in the second, is used in lawn mowers and for small
vehicles such as motorcycles. Other variations of the internal-combustion
engine include the Wankel engine, which replaces the piston and cylinder with a
triangular rotor moving inside an oval chamber, and the Diesel Engine.