A combustion chamber is part of an engine in which fuel is burned. The leftover hot gases produced by this combustion tend to occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber. This pressure can be used to do work, for example, to drive a piston in an internal combustion engine or to produce thrust when directed out of a nozzle as in a rocket or jet engine.
The combustionchamber consists of a cylinder, usually fixed, that is closed at one end and in which a close-fitting piston slides.
At the moment when the piston reaches the end of this stroke and the volume of the combustionchamber is at a minimum, the fuel mixture is ignited by the spark plug and burns, expanding and exerting a pressure on the piston, which is then driven away from the cylinder head in the third stroke.
At the end of the compression stroke, vaporized fuel is injected into the combustionchamber and burns instantly because of the high temperature of the air in the chamber.
Various shapes of combustionchamber have been used, such as L-head (or flathead) for side-valve engines, "bathtub","hemispherical" and "wedge" for overhead valve engines and "pent-roof" for engines having 3, 4 or 5 valves per cylinder.
The shape of the chamber has a marked effect on power output, efficiency and harmful emissions; the designer's objectives are to burn all of the mixture as completely as possible while avoiding excessive temperatures (which create NOx).
The term combustionchamber is also used to refer to an additional space between the firebox and boiler in a steam locomotive.
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