Comprehensive mechanism for the gas-phase oxidation of propene

This paper presents a first test of the extension of our computer code EXGA S to the generation of detailed mechanisms for the oxidation and combustion of alkenes. In the first part, an analysis of the elementary reactions fro m the literature allowed us to define new specific generic reactions involv ing alkenes and their free radicals, as well as correlations to estimate th e related rate constants. The corresponding generic rules were then impleme nted in the EXGAS code. The second part, a mechanism for the oxidation of propene involving 262 spe cies and including 1295 reactions was generated by EXGAS. The predictions o f this mechanism were compared, without any change of the best available ki netic data, with two sets of experimental measurements: the first obtained in a static vessel between 580 K and 740 K; the second used a jet-stirred r eactor between 900 K and 1200 K. If one takes into account that no fitting of individual rate constants was done, the mechanism reproduces correctly b oth the negative temperature coefficient (NTC) observed at approximate to 6 30 K and the variations of the concentrations with residence time of C3H6, CO, CO2, CH4, C2H2, C2H4, C2H2, C3H4, HCHO, CH3CHO, C2H3CHO, and cyclic eth ers (C3H6O), especially the general shape of these curves and their minima, maxima, and inflection points. Flux and sensitivity analyses were performed to get insight into the kineti c structure of the mechanism explaining the observed characteristics, such as the NTC or the autocatalytic behavior of the reaction. At low temperatur es, these analyses showed that the NTC is mainly due to the reversibility o f the addition to oxygen of the adducts, .C3H6OH, which via a mechanism sim ilar to that of alkyl radicals and involving two additions to oxygen, yield s degenerate branching agents. At high temperatures, in both kind of reacto r, the determining role of termination reactions involving the very abundan t allyl radicals has been emphasized, especially the recombination of allyl and hydroperoxyalkyl radicals, which is the main source of acrolein. (C) 2 001 by The Combustion Institute.