Detonation

A detonation is a wave of extremely violent Combustion, which is propagated at a speed Supersonique. The detonation occurs in a homogeneous mixture of gas Combustible and Comburant, or premixes, but also in condensed explosives. It is consisted a Shock wave being propagated in the mixture, immediately followed by a zone of reaction where combustion occurs. The shock wave is characterized by a brutal increase in the pressure and density, as well as a reduction the speed of gases. In the reference frame of the detonation, the speed of gases, which was supersonic in fresh gases, immediately becomes subsonic after the shock, and réaugmente in the zone of reaction. In the case of the detonation ideal, known as also of Chapman-Jouguet, speed becomes exactly equal to the speed of sound at exit of zone of reaction.

The speed of the Front of flame is thus much more important than in the case of a Déflagration: the face of flame is the face of the wave, it progresses more quickly than the sound in the medium, whereas in the case of the deflagration, speed is limited by the thermal Conduction and the Diffusion (see Flamme of premixing ). A detonation is propagated typically at a speed of several kilometers a second, to compare at a speed for the deflagrations about the meter a second and at a speed of sound in the air with room temperature of about 300 meters a second. The peak of pressure in a detonation is about 30 to 60 times the initial pressure. The numerical values of speed and pressure are even more important in the case of a detonation in a condensed explosive.

Beyond its use in the explosive , the detonation represents an security issue because it can occur in industrial accidents. In France, one can quote for example the catastrophe of factory AZF of Toulouse.

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