Shock-Tube Ignition Delay Time Measurements and Chemical Kinetics Modelling for Mixtures of Dimethyl Ether and Methane in Air

Dimethyl ether (DME) is a potential biofuel of interest due to its low sooting potential as well as its high cetane number (~55) which makes it a potential ignition enhancer for compression ignition engines. It has been shown that the addition of even a small amount of DME to methane increases the reactivity of the system significantly [1, 2]. In this study, ignition delay times for mixtures of DME and methane in air were measured behind reflected shock waves at pressures varying from 1.3 atm to 35 atm over the temperature range 900 K to 1650 K. Eight sets of mixtures have been investigated with equivalence ratios of 0.3, 0.5, 1.0 and 2.0. The rate constant for the unimolecular decomposition reaction CH3OCH3 (+M) = CH3O + CH3 (+M) has been re-estimated and a nine-parameter Troe fit generated to describe the reaction as a function of temperature and pressure. The resulting rate expression agrees well with that recently reported by Cook et al. [3] in the temperature range 1300–1700 K at 1.5 atm. A mechanism consisting of 118 species and 667 reactions was used to simulate the experimental data. Overall agreement between the model and experiments is found to be good