Flame Acceleration and Deflagration-to-Detonation Transition in Hydrogen-Oxygen Mixture in a Channel with Triangular Obstacles

Study of flame acceleration and deflagration-to-detonation transition (DDT) in obstructed channels is an important subject of research for hydrogen safety. Experiments and numerical simulations of DDT in channels equipped with triangular obstacles were conducted in this work. High-speed schlieren photography and pressure records were used to study the flame shape changes, flame propagation, and pressure build up in the experiments. In the simulations, the fully compressible reactive Navier–Stokes equations coupled with a calibrated chemical-diffusion model for stoichiometric hydrogen-oxygen mixture were solved using a high-order numerical method. The simulations were in good agreement with the experiments. The results show that the triangular obstacles significantly promote the flame acceleration and provide conditions for the occurrence of DDT. In the early stages of flame acceleration, vortices are generated in the gaps between adjacent obstacles, which is the main cause for the flame roll-up and distortion. A positive feedback mechanism between the combustiongenerated flow and flame propagation results in the variations of the size and velocity of vortices. The flame-vortex interactions cause flame fragmentation and consequently rapid growth in flame surface area, which further lead to flame acceleration. The initially laminar flame then develops into a turbulent flame with the creation of shocks, shock-flame interactions and various flame instabilities. The continuously arranged obstacles interact with shocks and flames and help to create environments in which a detonation can develop. Both flame collision and flame-shock interaction can give rise to detonation in the channels with triangular obstacles.