Using PLIF determined flame structure to analyze supersonic combustion efficiencies

A hydrogen-air flame was stabilized along the axis of a supersonic windtunnel which flowed Mach 2.5 coflow air. Planar laser induced fluorescence (PLIF) images of acetone vapor seeded in the fuel stream and OH produced in the reaction zone were collected from the supersonic combustor. A water cooled probe was employed to sample the gas downstream of the combustor to detect unburned fuel for combustion efficiency measurements. The combustion efficiency increased as the fuel mass flow rate was increased due to the increased flow blockage and heat addition. The PLIF images show that the fuel and air are premixed prior to reaction at the flame zone due to the intense recirculation at the fuel injector exit. Therefore the premixed gas either reacts at the flame zone or flows around it and exits the combustor. High fuel mass flow rate flames are larger and therefore react more efficiently.