Fuel-Air Mixing in Solid Fuel Scramjet Combustors

The mixing of non-reacting, turbulent, supersonic airflow with gaseous fuel added along the wall, has been studied. This arrangement is believed to simulate the fluid dynamic conditions encountered within a supersonic axisymmetric sudden expansion combustion chamber, employing solid fuel, whose decomposition gases are added or injected from the wall into the supersonic crossflow. A simplified order-of-magnitude analysis of characteristic times and rates is followed by detailed numerical solutions of the flowfield. A parametric investigation demonstrates the effect of wall injection velocity (from 0.5 to 4 m/s). The results reveal high fuel mass fractions within the recirculation zone attached to the inlet step. Downstream of the reattachment zone, fuel penetration towards the chamber centerline increases with axial distance. Mixing efficiency of the gaseous fuel with air varies from 100% for the lower injection velocity to about 46% at the higher injection velocity, indicating the potential for high burning efficiency in the case of reacting flows. Nomenclature A Cp D D G h k L i r Ρ Pk Pr S t Umix V V w Yi y Zr area specific heat grain port diameter diflusion coefficient mass flux total specific enthalpy turbulence kinetic energy combustor length Prandtl mixing length regression rate pressure turbulence kinetic energy generation rate Prandtl number source term time mixing velocity radial velocity velocity vector axial velocity mass fraction of species i distance from the wall normalized reattachment length Greek ε η κ μ ρ σ dissipation efficiency coefficient viscosity density effective Prandtl or Schmidt number Subscripts diff diffusive eff effective f fuel fR reactable fuel g gas phase lam laminar mix mixing res residence s solid phase turb turbulent