EFFECTS OF MIXING SCHEMES ON KEROSENE COMBUSTION IN A SUPERSONIC AIRSTREAM

A study of kerosene combustion in a supersonic vitiated airflow at Mac h 4.75 night enthalpy was conducted in direct-connect tests at Mach 1. 8 at a stagnation temperature of 1000 K. The effects of shock-and vort ex-enhanced mixing mechanisms on the combustion efficiency were evalua ted. Also included in this study were the effects of fuel heating and jet penetration. The experimental conditions corresponded to the low e nd of the hypersonic night regime, The following geometric configurati ons were employed: 1) a generic, rearward-facing step, 2) a modified r earward-facing step with beveled edges to facilitate vortex-enhanced m ixing, and 3) a rearward-facing wedge (15 or 30 deg) placed downstream of the rearward-facing step to induce shock-enhanced mixing, In all c onfigurations, a gaseous hydrogen-pilot jet was injected parallel to t he main flow from the base of the rearward-facing step and the liquid kerosene was injected normal to the main flow at three or five step he ights downstream of the step (the step height was 10 mm). Stable keros ene combustion was obtained for a maximum injected kerosene equivalenc e ratio of 0.86. For efficiency evaluation, the pilot-hydrogen equival ence ratio was selected between 0.02-0.04, while the kerosene equivale nce ratio was maintained at 0.325. In all experiments, locally rich st ratified kerosene combustion took place in a layer close to the inject ion wall. The wedge flameholder contributed to an increased kerosene c ombustion efficiency by the generation of shock-jet interactions. The beveled-edge step improved far-field mixing, thereby reducing the loca l kerosene equivalence ratio, resulting in the highest kerosene combus tion efficiency among all configurations tested. Fuel heating below le vels required for flash vaporization (one-third of the flash vaporizat ion energy, in this case) did not contribute to increased combustion e fficiency. On the contrary, this level of heating reduced the fuel den sity with adverse effects on penetration and mixing.