Comparative study on H-abstraction reactions of MPK and DEK initiated by OH and CH3 radicals: Kinetic insights and model refinements

Abstract

Elucidating the combustion chemistry of pentanone isomers provides critical insights into the reaction pathways of complex fuels and ketones with more than five carbon atoms. This study investigates the influence of OH and CH₃ radicals in the oxidation processes of pentanone isomers, employing multi-structural variational transition state theory in conjunction with small curvature tunneling effects to calculate H-abstraction rate constants and branching ratios for the 2-pentanone (MPK) + OH/CH₃ and 3-pentanone (DEK) + OH/CH₃ reaction systems across a temperature range of 200–1500 K. The findings reveal that multi-structural torsional anharmonicity significantly influences reaction rate constants and branching ratios, thereby altering the importance attributed to different reaction channels. In the MPK + OH system, the carbonyl group’s interaction with the transition state of reaction R1β, through hydrogen bonding, reduces the reaction barrier, rendering R1β the dominant pathway. For the MPK + CH₃ system, multi-structural torsional anharmonicity leads to channel competition, with R2α prevailing between 210–1400 K. In the DEK + OH system, R1*α takes precedence at temperatures exceeding 220 K. The total rate constants for the MPK + OH and DEK + OH systems, derived from our calculations, are presented with excellent agreement to the measurements, affirming the reliability of our computational approach. The specific expressions for these rate constants, are delineated as follows: $k_{R1}=0.0160\times T^{4.599}\exp (1916.431/T)$ and $k_{R^{\ast }1}=18.1368\times T^{3.714}\exp (1128.475/T)$ (cm³mol^-1sec^-1). Utilizing the computed rate constants, the Pieper, Kang, and Lin kinetic models are refined, enhancing the simulation accuracy of ignition delay times and species concentrations. Sensitivity analyses have been conducted to identify the pivotal reactions within the oxidation processes of MPK and DEK.