Kinetic modeling study of hydrogen addition effects on ignition characteristics of dimethyl ether at engine-relevant conditions

The effects of hydrogen on ignition characteristics of dimethyl ether (DME) with air under engine-relevant conditions were studied by CHEMKIN package coupled with chemical kinetic models. Firstly, four recently developed DME models were used to validate the measured ignition delay times from previous literature. The validation results showed that NUIG Mech_56.54 agrees the literature data best and thus was chosen to conduct the following simulations and chemical kinetic analysis of ignition behaviors of DME/H2 mixture at low temperature. Subsequently, simulations of auto-ignition of DME/H2/air using NUIG Mech_56.54 were made under various hydrogen blending ratios (0, 50%, 80%, 90%, 95%, 98% and 100%). It was found that hydrogen retarded the ignition timing of DME at engine-relevant conditions and this effect was non-linear with the increase of hydrogen blending ratio. The inhibition and non-linear effect was chemically interpreted by radical mole fraction analysis. Finally, reaction pathway and sensitivity analysis were made to gain further insight on ignition chemistries of DME/H2 blends under engine-relevant conditions.