Mass Spectrometric Characterization of the Partial Oxidation Process of a Gasoline Surrogate Induced by a Dielectric Barrier Discharge

Plasma-assisted combustion can improve the thermal efficiency and stability of internal combustion engines; based on this, among various types of discharge method, surface dielectric barrier discharge (SDBD) induced partial oxidation of hydrocarbons was investigated in this study. To demonstrate the general mechanisms of SDBD-induced partial oxidation of gasoline, we used a five-component gasoline surrogate (S5R), which consisted of a mixture of alkanes (isooctane, n-heptane, and methylcyclohexane), alkenes (trimethyl pentene isomers), and toluene, as the model. The detailed process of SDBD-induced partial oxidation of hydrocarbon was investigated by Fourier transform infrared spectroscopy, ion attachment mass spectrometry, and density functional theory calculation. SDBD irradiation of the hydrocarbon/air mixture induced dissociation of oxygen molecule through direct electron impact and collision with excited nitrogen molecules, and the resultant oxygen atom then reacted with a hydrocarbon molecule. Alkane and toluene were converted to alkyl hydroperoxide by a reaction with the oxygen atom and subsequent attachment of O₂. The resultant alkyl hydroperoxide then provided a ketone and/or aldehyde. In contrast, the alkenes underwent attachment of an oxygen atom and were either converted to fragments containing a carbonyl group or to etoposide. Regarding the analytical method, the partially oxidized products were selectively ionized from the hydrocarbon/air mixture when Na⁺ was used as the reagent ion for ion attachment mass spectrometry.