Implication of Sensitive Reactions to Ignition of Methyl Pentanoate: H-Abstraction Reactions by H and CH₃ Radicals

Abstract

Methyl pentanoate(MP) was identified as a potential candidate. To facilitate the application of MP with high efficiency in engines, a comprehensive understanding of combustion chemical kinetics of MP is necessary. In this work, the H-abstraction reactions from MP by H and CH₃ radicals, critical in controlling the initial fuel consumption, are theoretically investigated at the DLPNO-CCSD(T)/CBS(T-Q)//M06-2X/cc-pVTZ level of theory. The multistructural torsional(MS-T) anharmonicity is characterized using the dual-level MS-T method; the HF/3–21G and M06-2X/cc-pVTZ methods are chosen as the low- and high-level methods, respectively. The conventional transition state theory(TST) is employed to calculate the high-pressure limit rate constants at 298–2000 K with the Eckart tunneling correction. Our calculations indicate that the hydrogen atoms of the methylene functional group are easier to be abstracted by H and CH₃ radicals. The multistructural torsional anharmonicities of H-abstraction reactions MP+H/CH₃ are significant within the temperature range investigated. The tunneling effects are more pronounced at low temperatures, and contribute considerably to the rate constants below 500 K. The model from the work of Diévart et al. is updated with our calculations, and the simulations of the updated model are in excellent agreement with the reported ignition delay time of MP/O₂/Ar and MP/Air mixtures. The sensitivity analysis indicates that the H-abstraction reactions, MP+H-CH₃CH₂CHCH₂C(-O)OCH₃/CH₃CHCH₂CH₂C(-O)OCH₃+H₂, are critical in controlling the initial fuel consumption and ignition delay time of MP.

Keywords

Methyl pentanoate / H-Abstraction / Dual-level MS-T / Ignition delay time / Kinetic modeling

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