Detonation propagation, decay, and reinitiation in nonuniform gaseous mixtures

Abstract

Experiments on the behavior of detonation waves in nonuniform mixtures are presented. The situation studied was the propagation of a detonation wave from a driver mixture of variable length through a concentration gradient of variable width into a less reactive acceptor mixture. The effect of the gradient on the transmission process were studied. A detonation tube of 174 mm id. was used. The tube was initially divided by a fast-opening, stretched rubber diaphragm. Stoichiometric hydrogen/air mixture was used in the driver section. Hydrogen/air mixtures (14.0-19.0% H2) were used as acceptor mixtures. Natural diffusion was used to create a concentration gradient between two mixtures. It was shown that the behavior of detonations at concentration gradients depends significantly on the sharpness of the gradient. For relatively sharp gradients a detonation always decays in the nonuniform region. It can be reinitiated downstream in the acceptor mixture, if the driver length is large enough for a particular acceptor mixture. For relatively smooth gradients, detonation is able to propagate through without decay. The boundary between these cases is defined only by the value of sensitivity gradient for a particular pair of driver and acceptor mixtures. The critical value of the gradient depends strongly on the difference in energy content of driver and acceptor mixtures. The more overdriven is the detonation in the driver mixture compared to that in the acceptor, the sharper gradient is necessary for detonation decay. The order of magnitude of critical values of the gradient shows that evolution of the cellular structure may play a role effecting conditions for detonation decay at concentration gradients.