Oxidation of Ethylene-Air Mixtures at Elevated Pressures, Part 1: Experimental Results

Shock-tube experiments have been performed to determine ignition delay times of undiluted ethylene air mixtures for temperatures from 1003 to 1401 K, at equivalence ratios from 0.3 to 2.0, and at pressures from 1.1 to 24.9 atm. Ethylene was the focus of this study because of its importance in the oxidation of higher-order hydrocarbons. The data exhibited some interesting behavior not typically seen in other lower-order hydrocarbons. For example, the fuel-lean mixtures showed virtually no pressure dependence, whereas at stoichiometric and fuel-rich conditions the usual trend of decreasing ignition delay time with increasing pressure was seen. The results are compared with other experimental data available in the literature and to a chemical kinetics model that has been developed over the past few years using primarily high-pressure lower-order hydrocarbon ignition delay times. The original agreement between the model and experiments at the time the data were first obtained was fair at best, stressing the importance of the present data set for improving the understanding of the chemical kinetics of this important hydrocarbon species. A correlation for each mixture was developed with an ignition activation energy of around 42.4 k cal/mol for the fuel-lean and stoichiometric cases; this value reduced to 35.3 k cal/mol for the fuel-rich condition.