Deflagration

Deflagration (Lat: de + flagrare, "to burn down") is a term describing subsonic combustion propagating through heat transfer; hot burning material heats the next layer of cold material and ignites it. Most "fires" found in daily life, from flames to explosions, are deflagrations. Deflagration is different from detonation, which propagates supersonically through shock waves. This means that when a substance deflagrates, it burns extremely quickly instead of detonating. Black powder is an example of a substance that deflagrates; when it is ignited, black powder burns extremely quickly (so fast in fact that the burn is sometimes mistaken for a detonation).

In engineering applications, deflagrations are easier to control than detonations. Consequently, they are better suited when the goal is to move an object (a bullet in a gun, or a piston in an internal combustion engine) with the force of the expanding gas. Typical examples of deflagrations are the combustion of a gas-air mixture in a gas stove or a fuel-air mixture in an internal combustion engine, and the rapid burning of gunpowder in a firearm or of pyrotechnic mixtures in fireworks. Deflagration systems and products can also be used in mining, demolition and stone quarrying via gas pressure blasting as a beneficial alternative to high explosives.

Adding water to a burning hydrocarbon such as oil or wax produces a deflagration. The water boils rapidly and ejects the burning material as a fine spray of droplets. A deflagration then occurs as the fine mist of oil ignites and burns extremely rapidly. These are particularly common in chip pan fires, which are responsible for one in five household fires in Britain.

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