Detonation Diffraction Through a Mixture Gradient

Abstract

A simple one-dimensional model of a self-propagating gaseous detonation consists of a shock wave tightly coupled to a reaction zone, propagating through a combustible gas mixture as shown in Fig. 1 (Strehlow 1984). A feedback mechanism exists in that the shock wave generates the thermodynamic conditions under which the gas combusts, and the energy release from the reaction zone maintains the strength of the shock This is in contrast to a flame, or deflagrative combustion, in which thermal and species transport processes dominate. Given a particular set of initial conditions, a self-propagating detonation wave travels at a constant Chapman-Jouguet velocity (VCJ) on the order of a few thousand meters per second, with associated pressures and temperatures of tens of bar and several thousand degrees, respectively. A detonation is actually a three-dimensional shock-reaction zone complex with a dynamic wavefront composed of curved incident, mach stem, and transverse shock waves as depicted in Fig. 2 (Strehlow 1970). The transverse shocks sweep across the wavefront and the triple-point paths form a diamond-shaped cellular pattern. The cell width [Greek lambda] is a characteristic length scale of detonations, indicative of the coupling between gasdynamic and chemical processes.