Influence of the position of the double bond on theautoignition of linear alkenes at low temperature

摘要

The influence of the position of the double bond on the autoignition of linear alkenes has beeninvestigated by modeling the behavior of the three isomers of linear hexene and those of linear heptene.Low-temperature kinetic mechanisms for the oxidation of these six alkenes have been obtained after someimprovements made to the system EXGAS, for the automatic generation of mechanisms, which had beenpreviously adapted to model the oxidation of 1-pentene and 1-hexene. Quantum mechanical calculationshave shown that cis–trans conformations should be taken into account and that isomerizations of alkenyland alkenyl peroxy radicals involving a transition state including a double bond could be neglected. Thenew mechanisms have been validated using experimental data obtained in two rapid compression machinesbetween 600 and 900 K with a good prediction of cool flame and ignition delay times. The model reproduceswell the decreasing reactivity at low temperature when going from 1- to 3-alkene. While the profilesof products are well reproduced for 1-hexene in a jet-stirred reactor above 780 K, more problems areencountered for the prediction of products in a rapid compression machine at 707 K, showing persistingproblems in the understanding of the chemistry of the low-temperature oxidation of alkenes. Reactionrates analysis have been used to explain the difference of reactivity between the isomers of hexene.