Parametric Study of 3-D Hydrocarbon Scramjet Engine with Cavity *

Numerical calculations were completed to simulate the physical processes occurring within scramjet combustor flow fields and to determine the effects of different fuel injection schemes on the overall scramjet combustion efficiency. The different arrangements are compared in terms of species-mixing efficiency and overall combustion optimization. The numerical approach solves the full 3-D Navier-Stokes equations supplemented with a chemical combustion model including a rate-controlled kinetic mechanism for the combustion of ethylene fuel and air. The kinetic model is comprised of 20 chemical reactions and 13 chemical species, specifically, C2H4 (ethylene), C2H2, O2, CO2, H2O, CO, H2, OH, H,NO,N,N2 and O. The chemical model is directly coupled with a two-equation k-w turbulence model. For all cases, gaseous ethylene fuel is injected into the scramjet combustor region. The location of the fuel injectors and the angle of the injector orifices are varied to determine the optimum injection scheme. The fuel injector locations include the combustor inlet region upstream of the cavity, the cavity floor, and locations on the cavity upstream step and the downstream ramp. The angles of the fuel port injection slots include combinations of parallel, 27 deg, and 90 deg to the airflow inside the cavity. All combustor configurations include a common single-cavity combustor system to provide flameholding and stabilization in a supersonic combustor environment. The mixing efficiencies predicted for 10 different injection configurations are compared. The comparative results indicate that the fuel injection configuration with opposing injector pairs located within the cavity on the step and the ramp are the most efficient, resulting in 73-percent combustion efficiency. The work documented in this paper is part of an ongoing research program initiated with the goal of providing information to aid in the understanding of physical processes that dominate the flow within cavities utilized as scramjet combustor flameholders.