Instabilities in detonation waves near the limits of propagation

Abstract

Experimental work is described on the propagation of marginal detonation waves in propane-oxygen and hydrogen-oxygen systems diluted with oxygen, nitrogen and argon. The detonation tube was of rectangular section, with internal dimensions 2.3*1.0 cm, and overall length of 30 m. A continuous monitor of the wavefront velocity was achieved using a 3 cm wavelength microwave Doppler system. A cyclic wave phenomenon which is characterized by a normal and a slow velocity regime, is observed to be present near the limits of detonability in all except the hydrogen-oxygen-argon system. The relative durations of these regimes varies from one system to another and appears to be governed by the structural regularity of the detonation front. Schlieren records show that in the low-velocity regime the shock front and reaction zone are dissociated, with a separation varying between 1 and 10 cm, and that a weak transverse wave effect appears to be present at the lead shock which is non-planar.