Ignition Experiments of Hydrocarbons in a Mach 8 Shape-Transitioning Scramjet Engine

The design and testing of a cavity flameholder in a Mach 8 rectangular-to-elliptical shape-transitioning scramjet is presented. The experimental results presented are from the shock tunnel testing of the engine, fitted with the cavity combustor and fueled by gaseous ethylene, methane, and hydrogen. Axisymmetric simulations of a cavity in a diverging combustor were used to confirm that the cavity flow would fully establish in the limited test time available in our impulse facility. The cavity flameholder was designed such that autoignition and flameholding of gaseous ethylene-air mixtures should occur. Static pressure measurements were taken along the entire flowpath of engine. The engine was fueled at equivalence ratio ranging from 0.58<0.71. Successful combustion and flameholding of ethylene and hydrogen was observed at a flight Mach number of 7.3 and a dynamic pressure of 53.5kPa at an altitude of 28.7km. Methane did not ignite at any of the conditions tested.