Ignition and supersonic combustion behavior of liquid ethanol in a scramjet model combustor with cavity flame holder

This study carried out experiments to investigate the combustion behavior of ethanol at Mach 2.0 and stagnation temperatures between 1800 and 2200 K using a supersonic combustor with a cavity flame holder. The distribution of droplet diameters in fuel sprays was measured by a Laser Diffraction Spray Analyzer to estimate the vaporization time of fuel in the combustor. CH chemiluminescences and Schlieren photographs were measured by a video camera to identify the combustion mode and to measure the penetration height of fuel in the supersonic flow. Both gaseous and liquid ethanol injections were tested to examine the effect of the fuel vaporization process. The minimum equivalence ratio of injected fuel to air in the main flow and the minimum stagnation temperature for successful combustion were derived based on Weibull distribution statistics. Two combustion modes, intensive and transient, were identified based on the distribution of a rise in pressure and the CH chemiluminescence emissions over the cavity. Supersonic combustion was observed above the stagnation temperature of 2200-2000 K for liquid and gaseous ethanol injections. Compared with previous research, the reactivity of ethanol was located between the levels of ethane and ethylene. The ignition limits of the stagnation temperature for gaseous and liquid ethanol injections were also estimated and validated by calculating fuel breakup, vaporization, residence times and chemical reaction time. A fuel penetration height over 10 mm resulted in no supersonic combustion for the equivalence ratio of 1.0, although this enhanced fuel and air mixing. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.