Shock tube study of ethanol pyrolysis II: Rate constant measurements and modeling

The rate constants of two unimolecular decomposition channels of ethanol, C2H5OH(+Ar) = CH3 + CH2OH(+Ar), and C2H5OH(+Ar) = C2H4 + H2O(+Ar) were measured near 1 atm and 10 atm behind reflected shock waves between 1190 and 1550 K by tracking the evolution of CO and C2H4, respectively. Use of sensitive laser diagnostics in conjunction with carefully selected test mixtures enabled the suppression of sensitivity of CO and C2H4 time-histories to secondary reactions, resulting in a significant reduction of uncertainty in the measured rate constants. Additionally, CH3CHO time-histories measured during the pyrolysis of 2% C2H5OH/Argon mixtures were used to determine the rate constant of the most dominant H-abstraction channel, C2H5OH + H = sC2H4OH + H2 between 1290 and 1530 K. The low temperature CH3CHO time-histories were also used to infer the rate constant of sC2H4OH = CH3CHO+H. The measured rate constants were used to generate an updated kinetic model, whose performance was evaluated against the species time-history data reported in recent shock tube pyrolysis studies. The performance of the updated model was also evaluated against ignition delay times (IDTs) of stochiometric C2H5OH/Oxygen/Nitrogen mixtures, measured between 1000 and 1500 K near 20 atm in this study. The updated kinetic model was found to show excellent agreement with both shock tube pyrolysis and IDT studies. Additionally, the reduction in the uncertainty of the rate constants studied in this work resulted in a significant reduction in the uncertainty of the model predictions. The rate constant expressions listed below were derived from the measurements in this work, and are valid in the temperature range of 1200–1600 K.