Reaction and ignition delay times in the oxidation of propane

Empirical correlations between "reaction" and "ignition delay" times and the pressure, temperature, and composition have been obtained for propaneoxygenargon mixtures. Experiments were conducted by shock heating these mixtures to initial pressures and temperatures between 0.5 and 5.5 atm and 1000° and 1600°K for equivalence ratios and dilutions in the ranges 0.1 to 1.5 and 80 to 99% Ar, respectively. The radiation emitted behind incident shock waves was monitored as a function of time simultaneously in 9 spectral channels in the wavelength range 0.23-5.1//, and the refractive index gradient-time profile was recorded using a laser-schlieren technique. Reaction times were determined from 1) the cessation of CO2 formation, 2) the termination of OH emission, and 3) termination of the refractive index gradient signal; the ignition delay times were determined from 1) an initial rise in OH emission, 2) a second rise in OH emission, and 3) the initial rise in CO2 emission. The ratio of the reaction to the ignition delay time was found to be significantly greater than one and in the case of most interest to SCRAM JET applications this ratio was as large as 50. The restrictions on the utility of the empirical correlations for reaction and ignition delay times resulting from the occurrence of detonations and the introduction of systematic error by shock wave attenuation, boundary-layer growth, flow instabilities, and the difficulty of transforming observations from laboratory to particle coordinates are discussed.