Numerical investigation of self-ignition characteristics of solid-fuel scramjet combustor

The self-ignition characteristics of a solid fuel under supersonic flow have been investigated theoretically and numerically. Time-dependent two-dimensional axisymmetric compressible Navier-Stokes equations and species transport equations are solved numerically. Turbulence closure is achieved using the shear stress transport k-ω model. Polymethylmethacrylate 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 by an eddy-dissipation model. The numerical results generally agree with the experimental data in the published literature. The flame spread and pressurization during the self-ignition of polymethylmethacrylate in the combustor have been studied. The effect of inlet flow conditions and the geometry of the combustor on self-ignition behavior have been analyzed. Three stages of flame spread (namely, heat accumulation, secondary recirculation zone self-ignition, and orderly flame spreading) are identified during the self-ignition transient. Pressurization in the combustor during the third stage is evident. Self-ignition of the solid fuel can be affected by three kinds of limits: namely, lean oxygen, rich oxygen, and total temperature inlet conditions. A relatively long and deep cavity is beneficial to establish self-ignition. It is suggested that a step-type cavity can enhance self-ignition performance.