Experimental investigation on the ignition limits of a kerosene-fueled cavity in model scramjet combustor

Abstract

The ignition limits of liquid kerosene injected upstream of a cavity flameholder using a spark plug are investigated in a model scramjet combustor with the isolator entrance Mach number of 2.52, the total pressure of 1.6 MPa, and stagnation temperature of 1486 K. The effects of injection pressure and mixing distance on ignition are studied. Flame dynamics and the evolution of the flow field during the ignition process are acquired through high-speed photography and Schlieren photography. For near-field injection, successful ignition of kerosene can only be achieved when the injection pressure is extremely low or in a higher injection pressure range. The ignition is failed due to the fuel-rich local equivalence ratio in the cavity recirculation zone when the injection pressure is in the middle of injection pressure range. For far-field injection, the ignition trend is totally opposite compared with near-field injection. The ratio of the fuel that the cavity can react completely to that consumed by the mainstream is extremely low due to the minimal mass exchange rate between the cavity and the mainstream. The local equivalence ratio in cavity is the controlling factor determining whether successful ignition could be achieved. Only local ignition with low combustion efficiency is achieved in the present single-cavity combustor. The flame could not spread to the mainstream due to the lower turbulence level weakening the interaction of combustion products in the recirculation zone with unburned reactants in the supersonic flow.