Comparison of characteristic time diagnostics for ignition and oxidation of fuel/oxidizer mixtures behind reflected shock waves

Various methods for determining characteristic times of shock-tube ignition and oxidation are compared. Onset and peak times were obtained from time histories for four different species (CH, CH*, OH, OH*) as predicted by a modern detailed kinetics mechanism. Appropriate submechanisms for CH* and OH* formation and quenching were added to the existing mechanism to differentiate the excited-state species from the ground-state molecules. The modeling focused on mixtures of acetylene or ethane with oxygen highly diluted in argon at high temperatures (1200-2050 K) and nearly atmospheric pressures. Using a detailed mechanism known to accurately simulate the shock-tube chemistry, emphasis was placed on cohesion of characteristic times among the species and the extent to which one may be used to predict another. Generally, ignition onset times were found to be more consistent than peak times, with OH peaking at times least typical of the group. Onset time versus inverse temperature curves based on any one species agree with those of the other three species to within 25% for the hydrocarbon mixtures and given mechanism utilized herein. Results suggest that ignition onset time should be used for greater consistency, and kinetics modeling of excited-state species such as OH* and CH* should be included if comparing to data obtained using chemiluminescence diagnostics