Role of concentration gradient in the re-initiation of H2/O2 detonation in a 90° bifurcated channel

This paper numerically investigates the effect of concentration gradient on the re-initiation process of H2/O2 detonation propagating from a vertical channel to a horizontal channel. Two different types of concentration gradient distribution are considered in this study: from fuel-rich near the upper wall to fuel-lean near the lower wall (gradient > 0), from fuel-rich near the lower wall to fuel-lean near the upper wall (gradient < 0). The results show that the detonation can be re-initiated successfully for the two different types of concentration gradient, but the formation modes of the transverse waves in the re-initiation process are different. When the gradient > 0, the transverse waves are mainly formed after the 2nd reflection. When the gradient < 0, the transverse waves are mainly formed after the 1st reflection. However, whether the concentration gradient > 0 or < 0, the transverse waves are mainly formed on the fuel-lean side. The earlier transverse waves are mainly originated from the transverse waves of the transverse detonation. The detonation speed under fuel-rich condition is much higher as predicted by 1D simulation in the current study, and a local reactant distribution from fuel-lean to fuel-rich is formed by the leading shock in the horizontal direction. Thus, the transverse waves of the transverse detonation on the fuel-lean side can overtake the Mach detonation. Furthermore, the number of the transverse waves decreases with steeper concentration gradient, leading to the cell structure more irregular and the detonation transition from multi-head mode to single-head mode.