Exploring chemical kinetics of plasma assisted oxidation of dimethyl ether (DME)

Abstract

Abstract Chemical kinetics of plasma assisted oxidation of dimethyl ether was investigated by photoionization molecular beam mass spectrometry (PI-MBMS) and kinetic modeling. A series of hydrocarbon and oxygenated intermediates, especially some fuel-specific oxygenated intermediates including methyl formate, ethyl methyl ether and dimethoxymethane, were identified by the measured mass spectra and photoionization efficiency (PIE) curves. The quantification results displayed two main change patterns of species mole fractions with increasing oxygen, indicating the different dominating formation pathways. In addition to the oxygenates, C1 and C2 hydrocarbon intermediates were observed at low temperatures in the DME/O2/Ar and DME/Ar plasma systems, while the formation of these intermediates usually occurs at temperatures higher than 800 K in the thermal oxidation of DME. A kinetic model containing gas-phase reactions and plasma reactions was developed. The model analysis suggests that both hydrogen abstractions and plasma reactions involving electron/Ar*/O(1D)/Ar+ contribute to the fuel consumption. The subsequent reactions of the resulting CH3OCH2, CH3O and CH3 lead to the yield of the observed hydrocarbons and oxygenates. The experimental results together with kinetic modeling indicate that the fuel and fuel radical may decompose into methyl radical, oxygen atom and formaldehyde directly, which account for the under prediction of formaldehyde and the observation of oxygenates with moderate concentrations in the DME/Ar plasma.