Deflagration to detonation transition

Deflagration to detonation transition (DDT) refers to a phenomenon in ignitable mixtures of a flammable gas and air (or oxygen) when a sudden transition takes place from a deflagration type of combustion to a detonation type of combustion. A deflagration is characterized by a subsonic flame propagation velocity, typically far eblow 100 m/s, and relative modest overpressures, say below 0.5 bar. The main mechanism of combustion propagation is of a flame front that moves forward through the gas mixture - in technical terms the reaction zone progresses through the medium by processes of combined molecular and/or turbulent diffusion of heat and mass. In contrast, a detonation is charactezed by supersonic flame propagation velocites, perhaps up to 2000 m/s, and substantial overpressures, up to 20 bars. The main mechanism of combustion propagation is of a powerful pressure wave that compresses the unburnt ahead of the wave to a temperature above the autoignition temperature. The effects of a detonation is usually devastation.