Supersonic Combustion with Supersonic Injection Through Diamond-Shaped Orifices

Supersonic injection through a diamond-shaped injector was applied to a direct-connect supersonic combustor with a diverging section, and mixing/combustion characteristics were experimentally investigated in a Mach 2.4 vitiated airflow at a total temperature of 2000 K, and were compared with those with sonic injection through a circular injector. Without any flame-holding devices installed, scramjet-mode combustion was attained in a wide range of fuel flow rate, in which supersonic injection through the diamond-shaped orifice resulted in slightly larger pressure rise in far field than sonic injection through the circular orifice. Regardless of the injection schemes (i.e., the orifice shape and the injection conditions), occurrence of pressure rise around the injector and resulting injectant plume/oblique shock train interaction drastically changed mixing characteristics and enhanced thrust production, and mixing characteristics became less sensitive to the injection schemes. They became almost insensitive to the injection schemes in dual-mode combustion. The supersonic injection through the diamond-shaped orifice had lesser ability to attain the pressure rise in near field than sonic injection through the circular orifice, however, the ability was enhanced by installation of a cavity and introduction of cavity fueling.