Simulation of Deflagration-To-Detonation Transition in Premixed CH 4-Air in Large-Scale Channels with Obstacles

The deflagration-to-detonation (DDT) transition of a stoichiometric methane-air gas mixture in a channel with obstacles is simulated using a reduced single-step reaction mechanism. The parameters of this chemical model are calibrated to produce properties of laminar flames and planar detonation waves that correspond to existing experimental and theoretical data. The model is further calibrated using experimental data of DDT in obstructed tubes. Two distinct regimes of flame propagation are identified: the quasi- detonation regime characterized by repeated initiations and failures of detonations and the choking regime for which DDT does not occur. The development of a flame into a particular propagation regime depends on the channel geometry. The physical mechanisms controlling the DDT are found to be the same as those identified for hydrogen-air mixtures, namely the formation of strong shock waves and Mach stems that locally raise the temperature in a region of unburned fuel above the ignition point, although the initiation of detonations depends strongly on the model parameters