Modeling ethylene combustion from low to high pressure

With the same reaction set, data have been modeled successfully from two ethylene-oxygen combustion systems at greatly different pressures. New data are from the Princeton flow reactor, a lower temperature (850–950 K) and high-pressure (5–10 atm) data set (=2.5). The second set is for a high-temperature ( Several reaction sets were tested, but only the present set demonstrated good agreement in both cases. A key difference between this set and previous ones lies in the modeling of the complex C2H3+O2 reaction. New rate constants were calculated based on recent findings regarding the potential energy surface of the C2H3+O2 system. In the 850–1600 K range that is crucial in these experiments, the product set CH2CHO+O was found to contribute much less than reported in earlier studies, and the HCO+CH2O channel dominated. The present reaction set predicted the species profiles in both cases with reasonable accuracy, allowing us to interpret and compare the reaction pathways over a wide range of conditions. In the low-pressure flame, C2H4 is mainly consumed by abstraction, while in the high-pressure system, abstraction (mainly by OH instead of H) competes with H addition that forms C2H5. In both cases, abstraction forms C2H3 that reacts with O2 to make HCO and CH2O and eventually CO and CO2 However, higher levels of C2H5 and HO2 at the high-pressure, lower temperature flow reactor condition drive distinct pathway differences. The key role of HO2 chemistry is particularly emphasized through the reaction CH2O+HO2. Model comparisons support a lower value of the rate constant for this reaction, consistent with that recommended by Hochgreb and Dryer.

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