Fuel-Air Injection Effects on Combustion in Cavity-Based Flameholders in a Supersonic Flow

摘要

The Air Force Research Lab, Propulsion Directorate, Wright-Patterson Air Force Base, Ohio has studied several designs regarding cavity flameholding for supersonic RAMJET (SCRAMJET) applications. The most recent of these studies have concluded that direct injection of ethylene fuel into the aft cavity ramp produced an efficient, robust flameholder given specific freestream condition and fuel flow rate. The main goals of this experiment are: 1) study the effect on combustion of direct fuel and air injection in the main flameholding cavity and 2) characterization of the operational limits (i.e., sustained combustion limits) over a variety of fuel and air flow rates. Direct injection of both fuel and air provided additional capability to tune the cavity such that a more stable decentralized flame results. The addition of air injection provided the most improvement over the baseline case (fuel only) near the upstream portion of the cavity close to the cavity step. Direct air injection provided a second source of oxygen to be consumed during the combustion process thereby expanding the operational limits drastically for each selected fuel flow. This experimental investigation was limited by the size of the flow controllers available and by the maximum allowable material temperature given cavity flow parameters. Lean blowout was not observed to be a function of injected air flow.