Modeling of the oxidation of large alkenes at low temperature

New kinetic mechanisms for the oxidation of 1-pentene and 1-hexene at low temperature have been developed that require important improvements of the kinetic rules used by the EXGAS system for the automatic generation of mechanisms. This paper details the changes or additions necessary for the definition of the specific generic reactions involving alkenes and their free radicals, as well as the correlations to estimate the related rate constants. Tests have been performed to verify that these improvements still allow good simulations in the case of propene. New mechanisms for the oxidation of 1-pentene and 1-hexene at low temperature have been thus generated and validated using experimental data obtained in a rapid compression machine between 600 and 900 K. The mechanism for the oxidation of 1-pentene has also been tested in a plug flow reactor between 654 and 716 K. Results reveal acceptable agreement between simulated and experimental data for autoignition delays and for the distribution of products. The analysis of mechanisms demonstrates the importance of new reaction pathways specific to long chain alkenes. This study confirms the significant role played in autoignition delays by the reaction of addition of hydroxyl radicals to the double bond and by the specific reactivity of the allylic radical. The important role played by the reactions of allylic and alkenyl radicals with O2 to produce dienes is also emphasized and has allowed us to refine the kinetic value for these generic reactions.