Numerical investigation on self-ignition and flammability characteristics in solid fuel scramjet combustor

The characteristics of self-ignition and self-sustained combustion of a solid fuel under supersonic cross flow have been investigated theoretically and numerically. A time dependent two-dimensional, axisymmetric compressible Navier-Stokes equations and species transport equations are solved numerically. Turbulence model is using the Shear Stress Transport k-ω model. The PMMA fuel and a global one step reaction mechanism are used in this study. The reaction rate is determined by finite-rate chemical kinetics with the turbulence-chemistry interaction modeled using eddy-dissipation model. The numerical model is validated by comparing the numerical results with experimental data. The flame spread and pressurization during self-ignition of PMMA in combustor have been studied. The behaviors of both sustained and un-sustained combustion in SFSCRJ combustor have been analyzed. The simulation results reveal that three stages of flame spread are identified during the self-ignition transient, which consists of heat accumulation, self-ignition in the secondary recirculation zone, and whole combustor self-ignition orderly. The pressure suddenly rises in combustor during the third stage. The difference of combustor shape affects the self-ignition. There have always been high temperature zone and high mass fraction of reaction products in combustor during sustained combustion. Once the recirculation zone area and residual time provided by cavity are unable to meet the time needed for chemical reaction of reactants and the ignition of fresh mixture, flame is blew out by supersonic cross flow.