Effects of Fuel Preinjection on Mixing in Mach 1.6 Airflow

The effects of injection behind a pylon upstream of a supersonic combustion chamber were evaluated for liquid JP-10 and gaseous ethylene. A generic, rearward-facing, rectangular step was used as the primary flame-holding mechanism. A pilot-hydrogen flame injected from the base of the step provided ignition. The fuel was injected from a 1.5-mm-diameter wall orifice behind a thin triangular cross section pylon placed in the isolator at 10 step heights upstream of the step. The role of the pylon is to facilitate the penetration and the spreading of the liquid jet. Tests were performed under connected-pipe conditions in a Mach 1.6 airflow channel and air stagnation temperatures to 900 K, corresponding to the beginning of the hypersonic flight regime. The hydrogen, ethylene, and JP-10 flow rates were modulated during the tests, and wall pressures and temperatures were measured along the duct and in the recirculation region. Shadowgraph imaging indicated the effect of injection on the isolator shock train and the combustion chamber mixing. Combustion without upstream flashback was observed with isolator JP-10 equivalence ratios to 0.5. (Author)