Effect of Fin-Guided Fuel Injection on Dual-Mode Scramjet Operation

Abstract

Supersonic combustion experiments were conducted to determine the effect of a mixing enhancement fin on the combustion operation and reaction zone characteristics of a dual-mode scramjet. This fin-guided fuel injection approach was compared against a baseline that used no fin. A direct-connect vitiated-air facility was used to simulate the total enthalpy of a Mach 4.4 flight condition and generate a Mach 1.9 flow at the isolator inlet. Laboratory-scale tests were performed in a model combustor designed with a cavity flame holder and a 2 deg expansion. The experiments used hydrogen fuel at an overall equivalence ratio ranging between 0.05 and 0.25. The combustor flowfield was qualitatively analyzed using schlieren and chemiluminescence imaging, whereas quantitative assessments were made by comparing wall pressure distributions and exit temperature measurements. Low jet penetration with the baseline supplied the cavity with ample fuel, which concentrated the heat release and thermally choked the flow for an equivalence ratio higher than 0.10. Increased jet penetration with fin-guided injection displaced the reaction downstream of the cavity, enabling supersonic combustion up to an equivalence ratio of 0.15 but generating a flame 81–182% longer compared to the baseline. Practical considerations of using fin-guided fuel injection in a real system are discussed.