Experimental Investigation and scaling analysis of combustion stability in a Liquid-Fueled Ramjet

Ramjet engines are the most efficient propulsion method for flight at supersonic velocities between Mach 2.5-5. The air temperature and pressure at the combustor inlet depend on the flight Mach number and the inlet and nozzle design, with pressures typically in the range of 1 atm to 15 atm and temperatures between 600 K to 1200 K. Flame stabilization in liquid-fueled ramjets is generally obtained using axis-symmetric bluff bodies. An important metric for engine performance is the lean blowoff limit – the lowest equivalence ratio at which stable combustion can persist. Previous studies on the scaling parameters of blowoff limits in axis-symmetric bluff body flame holders have been based mostly on experimental measurements at atmospheric pressure and temperature and using gaseous fuel. In this work, we generated comprehensive experimental data on the lean blowoff limits of JP-8 fueled ramjets over the entire range of pressures, temperatures, inlet Mach number, and Reynolds numbers of interest. We critically revisited the existing scaling models using the new data, showing their limitations, and proposed a new scaling methodology for defining a lean blowoff Damköhler number. The new scaling method can be useful for predicting the change in the lean blowoff limit due to variations in operating conditions or flame holder size.