Computational investigation of an ethylene-fueled supersonic combustor assisted by a porous cylindrical burner

Abstract

To facilitate burning of ethylene fuel in a scramjet combustor, as a relevant route to hydrocarbon combustion, we propose an alternative design of configuration. Three-dimensional flow field in a strut-based scramjet combustor has been investigated computationally. The Large Eddy Simulation (LES) turbulence model and Partially Stirred Reactor (PaSR) combustion model are used. Validations have been performed against published literature to ensure the numerical settings and accuracy. It is shown that, while hydrogen can be successfully ignited and lead to stabilized flame, ethylene combustion cannot be sustained in the same way. By adding a porous cylindrical burner at downstream of the strut injector, consequently, continuous ignition and flame sustainment of ethylene in the primitive combustor can be achieved. To understand the essential difference, the key factors such as net thrust, momentum and pressure variations, flame extinction, and flame stabilization mechanisms have been studied. Specifically, while the porous cylinder may provide a re-ignition source for the hot flow quenched upstream, it expectably introduces a bow shock and extra drag when being placed at the downstream supersonic region. When the porous burner is inserted right behind the strut where the flow is locally subsonic, however, no shock is formed additionally and the total drag is not significantly increased while flames can be stabilized downstream of the porous burner. As a consequence, a positive net thrust and specific impulse at the same flow rate of fuel mass can be obtained, in contrast to the decelerating state in the primitive configuration that yields a negative thrust. Furthermore, the auxiliary device renders a larger penetrating depth of the injected fuel and flame spreading area as well as higher consumption ratio of oxygen, leading to a more favorable condition of design for a supersonic nozzle to produce effective propulsion.