Self-Ignition and Transition to Flame-Holding in a Model Scramjet Combustor.

Numerical simulations are conducted to investigate the self-ignition and its transition to stable flame-holding in a scramjet combustor with a backward step. A full three dimensional Navier-Stokes equation with a detailed chemical reaction model is solved with varying the location of the fuel injector and the geometry of the combustor. The results show that self-ignition occurs in the boundary layer developed on the injector-side wall. The initial reacting zone expands downstream and toward the recirculation zone behind the step. In the presence of precombustion shock wave (PSW), the reaction in the rear part of the combustor develops into the intensive flame because the PSW much increases the local Damkohler number. On the other hand, the reaction in the recirculation zone has very little effect on the generation of the intensive flame. The self-ignition can be governed by either near-field or far-field phenomena while the transition to the bulk flame is governed by far-field phenomena.