Fuel–Air Mixing Experiments in a Directly Fueled Supersonic Cavity Flameholder

Abstract

In the present study, planar laser-induced acetone fluorescence was used to quantify the streamwise concentration distribution of an ethylene fuel surrogate (acetone-seeded nitrogen) injected directly into the recirculation region of a cavity flameholder embedded in a nonreacting supersonic airflow. The effect of injection configuration and fueling rate were studied. Parallel injection from the cavity front wall resulted in an ultra-fuel-rich recirculation region (beyond the upper flammability limit of an ethylene–air mixture) with a mixing efficiency that degraded with increased fueling rate. Downstream angled injection from the cavity floor yielded a substantial improvement in terms of the spatial uniformity and flammability of the local mixture. Its mixing efficiency was observed to be independent of fueling rate. The superior mixing ability of the latter injection configuration has the potential to provide increased cavity flameholder operability through a broader range of ignition and blowout limits and more flexibility in terms of ignitor placement than conventional direct-fueling schemes. Further investigation of its performance over a wider range of reacting conditions is warranted.