Numerical simulation of flame acceleration and deflagration-to-detonation transition in ammonia-hydrogen–oxygen mixtures

Flame propagation and Deflagration-to-Detonation Transition (DDT) in a two-dimensional obstructed channel filled with stoichiometric ammonia-hydrogen-oxygen mixtures are simulated with detailed chemistry. For mixtures of high ammonia molar ratio (α = 4:1 and 2:1), a hot spot with high temperature appears in the unreacted material, and then DDT is triggered by the reactivity gradient inside a pocket of unreacted material for α = 2:1. However, for α = 4:1, detonative initiation and failure alternatively occur. For mixtures with low ammonia ratios, the DDT is triggered when the flame interacts with the reflected shock waves from either the bottom wall or the obstacle. Furthermore, as the concentration of ammonia decreases, the flame acceleration, the appearance of noticeable shocks and the deflagration-to-detonation transition occur at an earlier instant, and the ultimate propagation velocities of detonation wave increase. The flame cannot propagate stably in premixed ammonia-oxygen mixture without hydrogen with the ignition mode adopted in this study.