Geometric influence on the propagation of the quasi-detonations in a stoichiometric H2-O2 mixture

Abstract

Combustion wave propagation was studied experimentally in an obstructed narrow channel filled with stoichiometric H2-O2 mixtures using a simultaneous schlieren and soot foil technique. The propagation modes uncovered were classified as fast-flames, discontinuous detonation, and continuous detonation. In this study blockage ratio (BR) was found to have a strong effect on the detonation limit. For BRs of 33% and 66%, the ratio of the obstacle opening and detonation cell size (d/λ) at the detonation limit was found to be 0.6 and 6.0, respectively. This order of magnitude change in the detonation limit was found to be governed by a change in propagation mechanism associated with the discontinuous detonation mode. For all BRs the discontinuous mode is characterized by detonation failure, as it diffracts through the obstacle opening, and then re-initiation. For the low BR obstacles detonation re-initiation is driven by the generation of a detonation Mach stem that propagates along the top and bottom walls following oblique reflection of the decoupled detonation leading shock wave. For the high BR obstacles shock reflection off the top and bottom walls does not produce a detonation wave, instead a detonation is initiated at the proceeding obstacle face following a roughly normal reflection of the leading shock. These propagation mechanisms are not governed by obstacle BR, but rather the obstacle height and spacing is the key parameter as they control the strength of the shock at the point of reflection.