Re-initiation of detonation wave behind slit-plate

Abstract

The study to investigate a quenching mechanism of detonation wave utilizing a slit is of particular importance by considering safety devices to suppress the detonation wave in industries where flammable gases are handled [1, 2]. The detonation wave propagated through the slit is disintegrated into a shock wave and a reaction front, since expansion waves generated at a corner of the slit have effects to decrease a temperature and reaction rate behind the shock wave. However, it is understood that the shock wave diffracted from the slit causes re-initiation and transited to detonation wave at downstream region, even though a diameter of open-area is smaller than critical tube diameter [1,2]. It is also well known that reaction front can accelerate rapidly to supersonic velocity when propagating over obstacles. Mitrovanov and Soloukhin [3] reported and was also confirmed by Edward et al. [4] that the critical value to distinguish the propagation of detonation wave is about 13λ for circular tube and about 10λ for rectangular channel, where λ is a cell size of stable detonation wave. A fundamental observation carried out by Moen et al. [5] clarified if the turbulence intensity is maintained by placing obstacles, the reaction rate and degree of turbulence become highly coupled. Furthermore, experiment and numerical simulation of decoupling and re-coupling processes behind sudden expansion of a tube were conducted by Pantow et al. [6] and Ohyagi et al. [7] to show re-initiation processes of detonation wave after decoupled by diffraction process. These results showed that reflected shock wave and Mach reflection could be a source to re-initiate a detonation wave. However, fundamental mechanisms of re-initiation processes of detonation wave by the interaction of shock wave with another shock wave or tube wall are still open questions. In this study, experiments are carried out in order to elucidate the re-initiation mechanisms of detonation wave by installing the slit-plate into a detonation tube filled with premixed gas of hydrogen and oxygen. A width of slit w, a distance between two slits x and initial pressure of test gas p0 are varied and re-initiation processes are visualized using high-speed image converter camera with schlieren optical system.