Flame acceleration and onset of detonation in inhomogeneous mixture of hydrogen-air in an obstructed channel

Abstract

Flame acceleration (FA) and deflagration-to-detonation transition (DDT) in combustible premixed gases is a complex process involving the flow and combustion phenomena. Practically, the combustible premixed gases are often inhomogeneous. The numerical study aims to explore the effects of different solid obstacle distribution patterns on the FA and DDT process in the inhomogeneous concentration field. Results show that the shape of detonation wave is arc-shaped due to the inhomogeneous hydrogen concentration, and the detonation initiation process can be classified into three types: i) detonation induced by the coupling of the flame surface and the high-pressure zone; ii) detonation induced by the interaction between flame surface and reflected shock wave; iii) detonation induced by the interaction between the oblique shock wave or Mach stem and obstacles in the flow field. Also, this study finds that the flame evolutions have experienced four velocity augmentation regions before the detonation initiation. Further, the rich hydrogen content in the aperture and the higher unilateral blockage ratio can both promote flame acceleration, and further shorten the run-up time of the DDT.