Oxidation of Dimethyl Ether and its Interaction with Nitrogen Oxides

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Abstract
The oxidation of dimethyl ether (DME) under flow reactor conditions has been studied experimentally and in terms of a detailed chemical kinetic model. The experiments were performed at atmospheric pressure in the temperature range 600–1500 K and at different air/fuel ratios. Of particular interest was the interaction of DME with nitrogen oxides. The results show that the oxidation of DME occurs readily at temperatures above 1000 K, largely independent of the stoichiometry. Addition of NO under stoichiometric and fuel‐rich conditions does not affect the oxidation chemistry for DME, but above 1100 K a minor amount of the NO is reduced to HCN and N2 in reburn‐type reactions. Addition of NO or NO2 under oxidizing conditions significantly enhances the oxidation rate of DME and shifts the temperature for onset of oxidation to lower values, a phenomenon similar to that of NOx‐sensitized oxidation of hydrocarbons.The proposed chemical kinetic model provides a good description of DME oxidation in the absence of nitrogen oxides. Under the conditions of the present study, the conversion of DME proceeds mainly through the high‐temperature mechanism, with little importance of the intermediate peroxy species. In the presence of NO or NO2, the reaction CH3 + NO2 ⇌ CH3O + NO, followed by dissociation of CH3O, readily provides H atoms and thereby promotes the oxidation. At lower temperatures the mechanism involves CH3OCH2O2 and CH3O2 radicals. While the effect of NOx generally is described satisfactorily by the model, deviations at lower temperatures may indicate inadequacies in the reaction subset for these peroxy species.