Flame Acceleration and Deflagration-to-Detonation Transition DDT

Pipeline deflagrations and detonations can be initiated by varions ignition sonrces. The flame proceeds from a slow flame throngh a faster accelerating tnrbnlent flame to a point where a shock wave forms and a detonation transition occnrs, resnlting in an overdriven detonation (see Fignre 4-3). A stable (steady state) detonation follows after the peak overdriven detonation pressnre snbsides. 

Chatrathi et al. (2001) recently reported some experiments on flame propagation in indnstrial scale piping. They presented data on deflagration propagation in three sizes of pipes (6-inches, 10-inches, and 16-inches) and three fnels (propane, ethylene, and hydrogen). The effects of bends were evalnated, bnt other piping system components were not evaln-ated. The conclnsions from this work are as follows  

Pipe diameter has an effect on flame propagadon. It is minimal in the range of L/D from 1 to —50. In this secdon of the pipe, the flame velocity is not affected by the diameter. Beyond an L/D of 50, flame speed increases with pipe diameter. 

Flame speed is proportional to the fnndamental bnrning velocity that is, as the fnndamental bnrning velocity increases, the flame speed increases. 

The length-to-diameter rados at DDT were fonnd to be as expected. They ranged from 60 to 70, decreasing with increasing velocity and slightly decreasing with pipe diameter. 

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