An analytical approximation for low- and high-temperature autoignition for dimethyl ether-air mixtures

Dimethyl ether has proven to be one of the most attractive alternatives to traditional fossil oil derived fuels for compression ignition engines. In this study, a skeletal mechanism consisting of 32 species and 49 elementary reactions, based on the detailed mechanism proposed by Fischer et al. [Int. J. Chem. Kinet. 32 (12) (2000) 713-740], is further reduced to a short 36-step mechanism describing first and second stage ignition as well as the rapid transition to final products. A global 4-step mechanism is derived by introducing steady state assumptions of intermediate species. An analytical solution for the ignition delay times of the first stage of ignition in the low temperature regime and the beginning of its transition to the intermediate temperature regime is presented. The important competition of the β-scission and the reaction with molecular oxygen of the hydroperoxy-methoxymethyl radical (C2OCH2O2H) is quantified by the introduction of a parameter β, related to the competition of chain-branching and chain-propagation. The calculated values agree very well with those of the 36-step mechanism. Also for the high temperature regime, an analytical solution is presented, which agrees well with the experiments and the values calculated with the 36-step mechanism.