Effects of the non-reactive layer on dynamic behaviors of H₂-Air detonations in a microchannel

Detonation waves propagating in a confined microchannel with the inhomogeneous medium are investigated numerically by solving the Euler equations coupled with a detailed chemical reaction model. The non-reactive layer with finite thickness is introduced into the reactive medium. Three variables, i.e., non-reactive layer thickness H_I, reactive layer thickness H_R and their ratio H_I/H_R, are varied to discuss their effects on propagation modes, detonation velocities and cellular structures in detail. The results indicate that increasing H_I or decreasing H_R is adverse to the self-sustaining propagation of the detonation waves, associated with the decrease of average velocity and the increase of detonation cell size. Additionally, the study introduces a dimensionless parameter, H_I/H_R, to evaluate the dynamic behaviors of detonation waves. This approach contrasts with prior research, which solely relied on H_R as a criterion and assumed the critical H_R to be unaffected by the non-reactive gas layer. With the increase of H_I/H_R, the propagation mode of detonation wave will change from the stable state to the unstable state. And there is a critical value H_I/H_R. Exceeding this value, the detonation waves cannot propagate continuously in the millimeter-scaled channel. Notably, the critical H_I/H_R is constant (H_I/H_R ≈ 0.165) for the microchannel when the channel width H_T is less than 10 mm, implying the H_R is linearly correlated with the H_I. This key finding has been omitted by previous studies because their non-reactive layers are usually assumed to be infinite. As H_T increases beyond 10 mm, the critical value of H_I/H_R also rises. When H_T approaches infinity, H_I/H_R similarly trends toward infinity, suggesting that the critical H_R becomes independent of H_I. These phenomena show that the thickness of the non-reactive layer in the microchannel needs to be carefully addressed, and the coupling relationship of flow and heat release is different from the detonation wave in the macro-size channel.