Jie Chen , Qi Chen , Nan Liu , Shanshan Ruan , Xianwu Jiang , Lidong Zhang
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引用次数: 0
Abstract
The chain-initial reactions of small-molecule alkane (CnH2n+2(n ≤ 4)) oxidation participated by electronically excited oxygen O2(a1Δg) are crucial for understanding the role of O2(a1Δg) in plasma-assisted combustion and fuel reforming. Accordingly, in the present work, the energy barriers for the reactions O2(X3Σg/a1Δg) + alkane (n ≤ 4) → products were investigated by using high-precision quantum calculations. Rate constants for each reaction channel within the temperature range of 300–1500 K were predicted based on transition state theory (TST), supplementing plasma kinetics parameters. The energy barriers and rate constants for methane and ethane oxidation dehydrogenation reactions showed good agreement with literature data, validating the accuracy of the computational method employed in this work. The calculations revealed that the dehydrogenation sites have vital impacts on the reaction system. The energy barriers of the reaction channels involved in O2(a1Δg) were reduced at different dehydrogenation sites. Specifically, the change rate of each reaction energy barrier at primary, secondary and tertiary site was about 40 %, 65 % and 65 %, respectively. The reactions involving O2(a1Δg) significantly increased the reaction rate coefficient, especially for single hydrogen abstraction at the secondary and tertiary sites. The effect of O2(a1Δg) on ignition promotion and its regularity were further studied through kinetic simulations. The results suggested that adding O2(a1Δg) reduces the ignition delay time (IDT) of small molecular alkanes by approximately one order of magnitude, attributed to variations in energy barrier and branching ratios of different reaction channels. Notably, the H-atom abstraction reaction on primary site showed the largest sensitivity in IDT at 800 K, particularly for propane and isobutane, with IDT change rates of 98.0 % and 96.3 %, respectively. This study provided reasonable rate coefficients for kinetic modeling of plasma-assisted alkane ignition.
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