Plasma-assisted low-temperature oxidation of n-butane: A synchrotron photoionization mass spectrometry and kinetic modeling study

Abstract

The chemical kinetics of plasma-assisted low-temperature oxidation of n-butane (n-C4H10, 340 K, 30 Torr) is investigated by synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and kinetic modeling. Species measurements are conducted in a flow reactor activated by a nanosecond discharge using SVUV-PIMS. Detailed species identification and quantification are reported in the present work. Fuel-specific oxygenated species including 2-butenal (2-C3H5CHO), methyl vinyl ketone (CH3COC2H3), butanone (CH3COC2H5), butanal (n-C3H7CHO), 2-methyloxetane (-CH(CH3)CH2CH2O-), 1,2-epoxybutane (-CH(C2H5)CH2O-), tetrahydrofuran (-CH2CH2CH2CH2O-), 1-/2-butanol (1-/2-C4H9OH), and butyl hydroperoxide (C4H9O2H) are detected. A kinetic model for n-C4H10 plasma is developed, which well predicts the mole fractions of most species observed in experiments. Kinetic modeling reveals that electron-impact reactions of n-C4H10 are the main sources for various C1-C4 alkenes, alkynes, and radicals. Therefore, these reactions have a significant effect on the fuel consumption pathways and species pool formation. Reactions involving alkyl peroxy (RO2), especially the self- and cross-reactions of RO2, are essential for RO2 depletion and the formation of alcohols, ketones, and aldehydes. On the other hand, the misprediction of the species detected in the system, such as C4 cyclic ethers, ethyl formate (HCOOC2H5), and acrolein (C2H3CHO), indicates that their formation pathways in the current mechanism are incompletely described. Further experimental and numerical research on these subjects is desired for the development of the kinetic models.