Combustion Chemistry and Modeling, Henry Curran, Day 5 Part 1

This lecture, part of the Princeton-CEFRC Combustion Summer School, focuses on the detailed chemistry of alkene oxidation and the development of kinetic mechanisms for combustion. Henry Curran begins by discussing the influence of double bonds on reactivity, particularly the role of allylic radicals and their resonance stabilization. He explains how allylic C-H bonds are weaker, leading to lower activation energies for abstraction, and how the addition of O2 to allylic radicals is less favorable, reducing low-temperature reactivity. The lecture then compares the reactivity of different hexene isomers, showing that 1-hexene is more reactive than 2-hexene and 3-hexene due to the availability of secondary allylic sites that can participate in chain-branching pathways. Curran also discusses the importance of reactions such as alkene + HO2 in activating the chemistry. He then transitions to the broader context of building kinetic mechanisms for larger fuel molecules, emphasizing the need for accurate thermochemistry and rate constants. He highlights the case of dimethyl ether, which, despite containing oxygen, follows similar low-temperature oxidation pathways as alkanes. The lecture concludes with a detailed discussion of updating reaction classes in mechanisms, specifically the inclusion of additional pathways for QOOH radicals, such as direct HO2 elimination and cyclic ether formation, which were previously omitted. Curran shows how incorporating these pathways, based on quantum chemistry calculations, can significantly affect model predictions.