Kinetic studies of ozone assisted low temperature oxidation of dimethyl ether in a flow reactor using molecular-beam mass spectrometry

The ozone assisted low temperature oxidation chemistry of dimethyl ether (DME) from 400 K to 750 K has been investigated in the mixture of DME/O₃/O₂/He/Ar in an atmospheric-pressure flow reactor coupled with the molecular beam mass spectrometry (MBMS) sampling technique. The mole fraction of ozone was varied from 0 to 0.146% in the mixture to study its enhanced kinetic effect on DME oxidation. The mole fractions of DME, O₂, O₃, CH₂O, H₂O₂, CO, CO₂, and CH₃OCHO were quantified as functions of temperature at a fixed total volumetric flow rate. The experimental results revealed that the presence of ozone dramatically enhances the low temperature DME oxidation. Numerical simulations using the existing kinetic models (Kurimoto's model (KM) (Kurimoto et al., 2015), Burke's model (BM) (Burke et al., 2015), and Wang's model (WM) (Wang et al., 2015)) with an ozone sub-mechanism over-predicted the DME oxidation significantly. The observed large discrepancies between models and experiments for DME, CH₂O, O₂ and CH₃OCHO mole fractions suggested that there were large uncertainties in the branching ratios of two competing chain-propagation and chain-branching reaction pairs involving CH₃OCH₂O₂ and CH₂OCH₂O₂H radicals at low temperature.