An experimental study on the onset processes of detonation waves downstream of a perforated plate

Detonation waves propagating steadily in a rectangular tube were destroyed upon transmission through a perforated plate placed perpendicular to the direction of propagation. Subsequent re-initiation of the detonation waves downstream are investigated. Two explosive mixtures of C2H2+2.5O2+70%Ar (stable detonation with regular cellular pattern) and H2+N2O (unstable detonation with irregular cellular structure) are studied to illustrate the difference in the re-initiation processes. Simultaneous schlieren photography and smoked foil record permit the different features of the onset of detonation in the stable and unstable mixtures to be observed and analyzed in detail. It is found that two types of re-initiation processes are present. In the stable mixture, the onset of detonation is via multiple localized explosions distributed in the reaction zone, which gradually couple the reaction zones with the precursor shock to develop the original cellular structures. Whereas in the unstable mixtures, local perturbations usually at the boundary layer region near the wall lead to one or two strong local explosions forming overdriven detonation wave that decay to C–J detonation subsequently.