AN EXPERIMENTAL STUDY OF SPHERICAL GASEOUS DETONATION WAVES

Results are reported of an experimental study of spherical reacting shock waves and detonation waves using laser spark initiation. The motivation for this work is to further the understanding of the fundamental mechanisms of gaseous detonative combustion. The approach has been to isolate such mechanisms to their most elemental form by studying spherical reacting fronts, a geometry devoid of all confinement and other interference effects. Based on the magnitude of the initiation energy, distinct regimes of global propagation of such waves are established experimentally. These are constituted by the sub-critical energy regime where decoupling of shock and reaction zone occurs, the super-critical energy regime where the initially overdriven spherical detonation decays asymptotically to its C-J state and the critical energy regime where decoupling first occurs followed by re-establishment of a highly asymmetrical multiheaded detonation. Re-establishment occurs through the formation of 'detonation bubbles' in what is essentially a quasi-steady spherical shock-reacting front complex. The conditions within the quasi-steady complex were found to fall near the limits of auto-ignition. There is strong evidence in the work to suggest that the process of ignition by 'micro-explosions' that is explicitly observed near the limits of auto-ignition is universal to all cases where autoignition is possible. As such these 'micro-explosions' loom as the essential mechanism responsible for the formation of the transverse wave structure in gaseous detonation waves. (Author)