Unraveling Interaction Chemistry between Saturated Methyl Esters and Nitrogen Dioxide: An Ab Initio Kinetic Study on H‑Atom Abstraction Reactions

The
kinetic interactions between fuel molecules and nitrogen dioxide
(NO2) play a central role in fuel ignition and combustion
characteristics in advanced combustion engines equipped with exhaust
gas recirculation (EGR). This study presents the first theoretical
calculations to unravel the interaction chemistry between methyl esters
and the methyl ethers and NO2. High-level ab initio kinetic calculations were carried out to investigate H-atom abstraction
reactions from C2–C5 saturated methyl esters by NO2. Five small molecule esters, including methyl formate, methyl ethanoate,
methyl propanoate, methyl butanoate, and methyl iso-butanoate, were considered, encompassing 42 distinct H-atom abstraction
reaction channels. The CCSD(T)/CBS//M06-2X/6-311++G(d,p)
level of theory was employed to calculate the potential energy surfaces.
The conventional transition state theory was adopted to calculate
the rate coefficients within a temperature range of 400–2000
K. The effect of fuel molecular structures was analyzed via a systematic
comparison. The rate rules for H-atom abstraction reactions from different
carbon sites of methyl esters were proposed. The rate coefficients
reported in this study are beneficial for developing reliable combustion
kinetic models for methyl esters or real biodiesel interactions with
nitrogen oxides.