Kinetic insights into plasma-assisted low-temperature oxidation of propane with synchrotron photoionization mass spectrometry

Abstract

The present study investigates the chemical kinetics of low-temperature oxidation of propane activated by nanosecond pulsed dielectric barrier discharge in a flow reactor. Molecular beam mass spectrometry with tunable synchrotron vacuum ultraviolet photoionization (SVUV-PIMS) is employed for components identification and quantification. A series of hydrocarbons and oxygenated intermediates are observed, including fuel-specific species reported for the first time in this system like propyl hydroperoxide (C3H7OOH), acrolein (C3H4O2), oxetane (-CH2CH2CH2O-), methyloxirane (-CH(CH3)CH2O-), and propanol (n-/i-C3H7OH), which provide original kinetic information in the plasma-assisted low-temperature oxidation of propane. The detection of alkyl hydroperoxide (ROOH) demonstrates the existence of alkyl peroxy (RO2) formed through oxygen addition to alkyl (R) and the detection of cyclic ethers provides evidence for the presence of hydroperoxyl alkyl (QOOH). A kinetic model incorporating plasma chemistry and combustion chemistry is developed for plasma-assisted oxidation of propane. Path fluxes of fuel consumption and oxygenated intermediates formation are provided based on model analysis. Besides H abstractions by the OH radical, reactions activated by plasma involving electron impact dissociation, O(1D)/Ar* quenching dissociation, and ionization contribute much to fuel consumption. The formed propyl (n-/i-C3H7) are exclusively consumed through oxygen addition producing propyl peroxy (n-/i-C3H7O2). Propyl peroxy can participate in self- and cross-reactions yielding various oxygenated intermediates such as aldehydes, ketones, alcohols, and propoxy (n-/i-C3H7O). Discrepancies between simulations and experiments suggest that further kinetic studies on low-temperature mechanisms, including propyl peroxy related reactions for plasma-assisted combustion modeling, are still desired.