Impact of concentration gradient on detonation propagation in lean and rich hydrogen–oxygen mixtures

This study numerically investigates detonation propagation in H 2 /O 2 mixtures with fuel-lean or fuel-rich concentration gradients, a regime remains underexplored in prior research. By analyzing the flow field, distinct propagation mechanisms are identified for each mixture. The results show that the concentration gradients remarkably intensify cellular instability and induce pronounced oscillations in detonation velocity within the gradient region. In fuel-lean gradients, the detonation transitions from a multi-headed to a single-headed mode, driven by oblique shock interactions with the inhomogeneous mixture. In fuel-rich gradients, transverse detonation waves degenerate into shock waves at high equivalence ratios, inhibiting re-initiation near the upper wall. Under highly fuel-rich conditions, a unique coupled structure comprising a short detonation and a curved shock forms within the channel, accompanied by a Tulip-like flame. Moreover, complementary 1D simulations confirm that fuel-rich mixtures are more susceptible to decoupling, attributable to prolonged ignition delay times and attenuated leading-shock pressures. • 1D And 2D detonations in lean or rich concentration gradient mixtures are studied. • Detonation behavior in purely lean or rich H 2 /O 2 mixtures are compared. • Different detonation propagation modes are discussed. • 1D cases explained why detonation are prone to decoupling under rich combustion.