An experimental and modeling study of dimethyl ether/methanol blends autoignition at low temperature

New rapid compression machine (RCM) ignition delay data for dimethyl ether (DME), methanol (MeOH), and their blends are acquired at engine-relevant conditions (T = 600 K-890 K, P = 15 bar and 30 bar, and equivalence ratios of ϕ = 0.5, 1.0, and 2.0 in synthetic dry air). The data are then used to validate a detailed DME/MeOH model in conjunction with literature RCM and shock tube data for DME and MeOH. This detailed DME/MeOH model, constructed by systematically merging literature models for the combustion of the individual fuel constituents, is capable of accurately predicting the experimental ignition delay data at a wide range of temperatures and pressures. The experiments and simulations both show a non-linear promoting effect of DME addition on MeOH autoignition. Additional analyses are performed using the merged DME/MeOH model to gain deeper insight into the binary fuel blend autoignition, especially the promoting effect of DME on MeOH. It is found that the unimolecular decomposition of HO2CH2OCHO plays an essential role in low temperature DME/MeOH blend autoignition. The accumulation of HO2CH2OCHO before the first-stage ignition and later quick consumption not only triggers the first-stage ignition, but also causes the non-linear promoting effect by accumulating to higher levels at higher DME blending ratios. These analyses suggest the rate parameters of HO2CH2OCHO unimolecular decomposition are critical to accurately predict the first-stage and overall ignition delay times as well as the first-stage heat release profile for low temperature DME/MeOH oxidation.