Numerical Investigation of Methane and Air Mixing in a Shcramjet Inlet

The performance of gaseous methane-air mixing in the inlet of a shock-induced combustion ramjet is investigated in this paper. The two oblique shocks mixed-compression inlet configuration is selected to ensure the flow travels in a parallel direction to the internal mixin g duct. Cantilevered ramp injectors, designed to deliver rapid mixing in a high enthalpy flow, are incorporate d and strategically positioned at the external ramp. The inlet is designed to enable vehicles to travel at the Mach 8 flight speed and follow the 67032Pa flight dynamic pressure path at 28.6km altitude. The objective of this study is to evaluate the impact of inlet geometrical parameters, fuel injection properties, and injector dimensions on the mixing efficiency. The study also measures the inlet performance of other fuels commonly used for hypersonic vehicles such as kerosene and hydrogen. The analysis of three-dimensional steady state flowfields is undertaken numerically via the Window Allocatable Resolver for Propulsion (WARP) code. WARP solves the multispecies Favre-averaged Navier-Stokes equations, which are closed by the Wilcox k − ω turbulence model. The numerical results indicate that an air-based mixing efficiency of up to 0.85 can be achieved with a low risk of premature ignition. Both inlet wedge angle and fuel tank stagnation temperature are identified as having a significant influence on inlet performance. The applicability of the cantilevered ramp injector to the Mach 8 hydrocarbon inlet is validated and justified. Lastly, it is concluded that methan e delivers the best mixing performance among the 3 fuels, and the mixing efficiencies of the kerosene and hydrog en inlets are found to be comparable despite the difference in their molecular weights.