Chemical energy release in one-dimensional detonation waves in gaseous explosives

Abstract

The Zel'dovich-von Neumann-Doring (ZND) model of a one-dimensional, steady state detonation wave in a gaseous explosive is extended to include the thermal relaxation processes which precede and follow the exothermic chemical reconstitution reactions. In this nonequilibrium model the detonation wave consists of four main zones: a very thin leading shock front in which the unreacted explosive mixture is compressed and accelerated in the direction of shock propagation; a much thicker relaxation zone in which the rotational and vibrational modes of the unreacted explosive gases approach thermal equilibrium; a relatively thin zone in which the chemical energy is released by rapid chain propagation and branching reactions into highly vibrationally excited reaction product gases; and another very thick relaxation zone in which the product gases expand and vibrationally relax toward thermodynamic equilibrium at the Chapman-Jouguet (CJ) state. Quantitative calculations for the H 2Cl 2, O 3, and H 2O 2 systems based on experimental chemiluminescent and crossed molecular beam product energy distribution data show that the amount of chemical energy initially released as product vibrational energy is greater than the sum of CJ equilibrium vibrational energy plus the amount of chemical energy required to sustain the constant velocity shock front. The physical mechanism by which this vibrational energy sustains the shock front is postulated to be the chemical amplification of transverse pressure waves, which propagate through the vibrationally excited products and eventually overtake the leading shock front.