FUEL STAGNATION TEMPERATURE EFFECTS ON MIXING WITH SUPERSONIC COMBUSTION FLOWS

An experimental study of the effect of fuel stagnation temperature on mixing in a supersonic hydrogen-air flame is described, The combustor consisted of a constant-area rectangular duct with a centrally located fuel-injection strut that spanned the width. A high-enthalpy stream o f air was supplied by a free-piston shock tunnel, and heated hydrogen fuel, supplied by a gun-tunnel, was injected into the freestream as a coflowing planar jet. The freestream total enthalpies were 5.6, 6.5, a nd 9 MJ/kg, and fuel stagnation temperatures were 300, 450, and 700 K, Raising the fuel stagnation temperature increased the fuel velocity t o be near that of the airstream and resulted in a decrease in the mixi ng rate, Even as the fuel and air velocities became equal, significant mixing still occurred because of a large difference in density, Incre asing the freestream enthalpy reduced the difference between the initi al air temperature and the adiabatic flame temperature, which in turn reduced the heat addition, and subsequently, the amount of pressure ri se in the duct.