The quasi-steady regime in critically initiated detonation waves

Abstract

Experimental work is described on the initiation of spherical detonation waves, in oxyacetylene with various diluents, using an exploding wire and a lead azide pellet as sources. The transition of the spherical blast wave to a detonation, when the source energy is either above or at the critical value, is studied by three methods. Changes in wave structure are inferred from the cellular patterns obtained on smoked foils orientated radially to the flow: the wavefront velocity is derived from the Doppler frequencies and the pilot pressure variation is measured. For supercritical source energies the results obtained provide a detailed pressure history of the transition process. At critical source energy it is shown that the transverse wave structure, which is present in the initially overdriven wave, disappears when the low-velocity regime is established. The duration of the quasi-steady regime is approximately 10 mu s (or distance approximately 1 cm) before the establishment of a normal CJ wave.