Dimethyl ether (DME) is an alternative diesel fuel and an ideal fuel candidate for experimental kinetic studies of two-stage autoignition chemistry for internal combustion engines. OH, HO2, and H2O2 are key intermediate species that control the chemistry of autoignition, but experimental quantification of these chemical species remains challenging. We have recently carried out a detailed study of dimethyl ether oxidation in a flow reactor operated at atmospheric pressure over a temperature range of 500 to 1150 K. Molecular beam mass spectroscopy has been used to quantify H2O2, while dual wavelength dual modulation Faraday rotation spectroscopy (DW-DM-FRS) has been used for simultaneous in situ quantification of OH and HO2 at the exit of the flow reactor. The experimental measurements for OH, HO2, and H2O2 have been combined with measurements of stable species (CO, CO2, CH2O, and DME) using MBMS and gas chromatography and compared to predicted concentrations from a chemical kinetic model for DME oxidation. Agreement between the kinetic model and the experimental observations is excellent in the intermediate temperature region (900-1150 K), however, the model significantly over-predicts DME consumption and H2O2, OH, HO2, and CO production in the low-temperature region (500-650 K). Based on these results, it is proposed that a problem exists in the model associated with the branching ratio between QOOH (CH2OCH2OOH) decomposition and ketohydroperoxide formation (HO2CH2OCHO). The DME model favors ketohydroperoxide formation, resulting in an over-prediction of the fuel reactivity at low-temperatures. Modification of the model using a derived value for the branching ratio based on experimental measurements for the concentrations of DME, CH2O, and CO significantly improves agreement between the model and the experimental observations. In this talk we will summarize the results of our multi-diagnostic study of DME oxidation. We will also discuss our current understanding of DME low temperature chemistry and the uncertainty associated with the QOOH branching ratio.

Kinetic study of low and intermediate temperature oxidation of dimethyl ether

248th National Meeting (2014)

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