DETONATION AND

DEFLAGARATION- Jigar Dodia

Deflagration (Lat: de + flagrare, "to burn down")

Subsonic combustion propagating through heat transfer; hot burning material heats the next layer of cold material and ignites it.

A deflagration is characterized by a subsonic flame propagation velocity, typically far below 100 m/s, and relatively modest overpressures, say below 0.5 bar.

Most "fire" found in daily life, from flames to explosions, is deflagration.

Eg. Combustion in Gas stove, Fuel air mixture in IC Engine, Rapid burning of gunpowder in firearm, pyrotechnic mixture in fireworks.

Applications in mining, demolition and stone quarrying via gas pressure blasting.

Detonation (detonare, meaning “to expend thunder”)

Combustion propagation is of a powerful pressure wave that compresses the unburnt gas ahead of the wave to a temperature above the autoignition temperature.

The velocity of detonation in solid and liquid explosives is much higher than that in gaseous ones.

A detonation is characterized by supersonic flame propagation velocities, perhaps up to 2000 m/s, and substantial overpressures, up to 20 bars.

Detonation is most often used for explosives and the acceleration of projectiles.

Pulse detonation engines use the detonation wave for aerospace propulsion.

The Hugoniot-diagram

Deflagration to Detonation The natural acceleration of a flame in a long

pipe The forced acceleration of a less confined

mixture within a region containing obstacles

In both cases, gas phase turbulence enhances combustion rates to a point where a shock wave is formed ahead of the flame front. If further flame acceleration occurs, the leading shock wave is strengthened until a transition to detonation occurs.

Deflagration-to-Detonation Transition (DDT) Deflagration-to-detonation transition (DDT) is the transient

phenomenon resulting from the acceleration of a deflagration flame to detonation via combustion-generated turbulent flow and compressive heat effects.

During the DDT, the initial peak pressure reached is higher than the final pressure reached when the stable detonation phase occurs, and the detonation wave is described as “overdriven.”

Deflagration to Detonation Transition Caused Industrial Accidents

1970 Propane vapor cloud explosion in Port Hudson

Deflagration to Detonation Transition Caused Industrial Accidents

The Flixborough disaster

Deflagration to Detonation Transition Caused Industrial Accidents

The1989 Phillips Disaster in Pasadena, Texas

Deflagration to Detonation Transition Caused Industrial Accidents

The damage observed in the Buncefield fire, see the 2005 Hertfordshire Oil Storage Terminal fire

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