Simulation of Post-Detonation Reaction and Afterburning Process of High-Explosive Charges with Detailed Chemical Kinetics

The posted detonation reaction processes of high-explosive charges involves reaction inside of the high-pressure detonation products, dissociation of air by intense shock waves, and afterburning when fuel-rich detonation products mix with the surrounding air. The details of these reaction processes are not well understood. We present two-dimensional axisymmetric simulations of the reaction and afterburning that occurs in the expanding flow produced by the detonation of a PETN charge. The simulations used the Becker-Kistiakowky-Wilson real-gas equation of state with detailed chemical kinetics with 59 species and 368 reactions. A novel programmed burn model was used to approximate the detonation while allowing the gas-phase detonation products to react. The computed results show significant air dissociation by the shock wave as well as turbulent mixing and afterburning. Initially when the shock breaks out of the charge, the degress of air dissocision is large producing a N, O, and NO. Most of the N and O recombine as the shock expands and cools down. However, a large amount of NO remains for a significant period of time. Significant quantities of OH are produced in regions where the shock-heated air and fuel-rich detonation products mix and burn. The computed results also show that the chemical composition in the detonation products are essentially frozen once the temperature falls below 2000 K, which provides some evidence for the freeze-out assumption used in chemical equilibrium codes.