Propagation Mode of Detonation Waves in a Narrow Gap

Abstract

Propagation mode of detonation waves in a narrow gap has been studied experimentally. The gap was formed by a pair of metal plates of 1500 mm in length which were inserted in a detonation tube. Two metal spacers were interposed at both side edges of the plates to arrange a gap size of 2.0 mm. The plates are supported by 15 combination probes which were composed of pressure and ion probes. Using the combination probe it is possible to detect a shock and a reaction front individually at one measurement point. A test gas was hydrogen-oxygen mixture diluted with argon or nitrogen and an initial pressure was 39 kPa. Velocity profiles and smoked foil records reveal five propagation modes in the gap: stable, quasi-stable, galloping, single head, and failure mode. In the quasi-stable mode, the propagation velocity is almost constant, while cell size on smoked foil records has larger variation as compared to the stable mode. The galloping mode shows large velocity fluctuation more than ±500 m/s and wide variety of the cell size along the propagation direction. In the single head mode one triple point travels downstream reflecting at the sidewall. The velocity deficit normalized by the propagation velocity at the gap entrance is dependent on the gap size normalized by the cell size, although the velocity deficit has little dependency for lean hydrogen-oxygen mixtures.