Combustion chamber definition
The volume of the space in the cylinder above the piston with the piston at top dead center (TDC) in the compression stroke . The head of the piston , the cylinder walls , and the head form the chamber . Combustion of the fuel-air mixture begins here when ignited by a spark plug . The design and shape of the combustion chamber can affect power, fuel efficiency , and emissions of an engine. Also see hemispherical combustion chamber and wedge combustion chamber .