Numerical Simulation of Ignition in Supersonic Reactive Shear Layers

Abstract

This study is a direct numerical simulation of a spatially evolving reactive mixing layer of a hydrogen/air system. A second-order TVD scheme with full chemical mechanism was employed to observe the mixing and ignition process. Mixing efficiency and ignition location were investigated under different convection Mach numbers. Techniques for enhancing ignition are discussed, attention being given to the coupling of the shear layer growth rate and viscous dissipation. Results show that an increase of convective Mach number significantly decreases fuel-air mixing efficiency, but enhances the viscous dissipation. As a result, a decrease of shear layer thickness enhances the auto-ignition at high Mach numbers. It was also found that an increase of hydrogen velocity causes the shear layer to shift toward the air side, leading to a shorter ignition delay time. Furthermore, the effect of instability of the shear layer on ignition was also investigated. It was found that an improvement of ignition was-achieved by imposing a very small perturbation upstream.