Kinetic and Mechanistic Insights into H-Abstraction and Subsequent Isomerization and Decomposition of Monoglyme and
Chunyu Wang1, Tong Yan1, Jinsheng Zhang1
1School of Automotive and Traffic Engineering, Jiangsu University, Zhenjiang 212013, China.
Abstract:
To provide kinetic data for a key radical-induced subnetwork in the oxidation of oxygenated polyether fuels, the potential energy surfaces for H, CH3, OH, and HO2-mediated H-abstraction from monoglyme (MON, CH3OCH2CH2OCH3), together with the subsequent isomerization and β-scission decomposition reactions of the resulting fuel radicals, were constructed at the CCSD(T)/CBS//M06-2X/6-311++G (d, p) level. High-pressure-limit and pressure-dependent rate constants were predicted using master-equation calculations over 300-2000 K. The calculated H-abstraction barriers for MON range from -1.6 to 18.5 kcal mol-1, corresponding to the reactivity order of OH > H > CH3 > HO2. The site-dependent barriers are consistent with the calculated C-H bond dissociation energies (BDEs) and the stabilization of the resulting radicals. The subsequent isomerization is competitive at low temperatures. With increasing temperature, the C-O bond cleavage pathways become kinetically favored within the investigated post-H-abstraction unimolecular subnetwork, particularly the channel leading to methoxy acetaldehyde (CH3OCH2CHO). The H-abstraction of methoxy acetaldehyde by the four radicals mentioned above and the subsequent reactions were further investigated using the same methodology. The results indicate that the reactivity sequence of H-abstraction in methoxy acetaldehyde is consistent with that of MON. The methoxy acetaldehyde-derived radicals preferentially evolve through lower-barrier decomposition pathways rather than extensive isomerization. Comparisons with related ether systems and uncertainty analyses support the reliability of the calculated rate constants within the expected theoretical uncertainty. Implementation of the updated H-abstraction kinetics into a detailed MON oxidation mechanism affects the predicted ignition delay times. These results characterize the H-abstraction and subsequent unimolecular-reaction subnetwork from MON to methoxy acetaldehyde and smaller products, providing mechanism kinetic data for future refinement of oxygenated polyether combustion models.
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