Inside a rocket or jet engine, a space where fuel and oxidizer are burned in order to produce thrust. Turbojet engines, turbofans, ramjets, scramjets and rockets all have combustion chambers.

In an internal combustion engine, the combustion chamber is the space where combustion occurs. Usually it is defined by the space left clear in the cylinder head with both valves closed and the piston at top dead center.

The relationship between a cylinder's swept volume and the size of the combustion chamber is called the compression ratio. A smaller combustion chamber produces a higher compression ratio. This produces more power, but also higher tempratures, and greater danger of pre-ignition or pinging. This means that high octane fuel may be required.

Combustion chamber size may be changed in two ways. First of all, the head may be milled, reducing its height and shrinking the combustion chamber accordingly. Milling is expressed in thousandths of an inch, and .020 inches is a large mill. This is a common hot rodding trick. Second, the piston shape may be changed. A domed piston, shrinks the compression ratio, producing more power. A dished piston increases the combustion chamber, reducing compression. Auto manufacturers install all types of pistons, according to their desired application. Larger combustion chambers are favored for many applictions, because they allow more flexible fuel choices.

Com*bus"tion cham`ber. (Mech.)


A space over, or in front of , a boiler furnace where the gases from the fire become more thoroughly mixed and burnt.


The clearance space in the cylinder of an internal combustion engine where the charge is compressed and ignited.


© Webster 1913

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