Effect of hydrogen concentration distribution on flame acceleration and deflagration-to-detonation transition in staggered obstacle-laden channel

Abstract

A staggered arrangement of solid obstacles promotes flame acceleration (FA) and the deflagration-to-detonation transition (DDT) in a homogeneous concentration field. Many combustible premixed gases, however, are inhomogeneous. The present numerical study explores the effects of different hydrogen–air distributions on the FA and DDT processes in a staggered obstacle-laden channel. The results show that, in the early stage of flame evolution, the flame accelerates faster when there are no obstructions on the side of the channel with the high hydrogen concentration. Under the suction effect of the aperture formed between an obstacle and the wall, the flame experiences multiple periods of velocity augmentation during its evolution. In terms of detonation initiation, the process can be classified as either detonation induced by the interaction between the flame surface and the reflected shock wave from the wall/obstacle, or detonation induced by the collision between the leading shock wave and the reflected shock wave from the obstacle. As the detonation wave propagates, regions with a hydrogen content of less than 12.7 vol. % cause a decoupling of the detonation wave. The morphology of the detonation wave (length, angle, and height) is related to the specific distribution of the hydrogen concentration. From the overall FA and DDT processes, a more homogeneous hydrogen concentration distribution leads to faster flame state variations and a faster triggering of the detonation.