Dimethoxymethane low- and intermediate-temperature oxidation up to 100 atm

Dimethoxymethane (DMM) is a promising renewable fuel with low-carbon intensity and low tendencies for soot and NO_x emissions, which is drawing increasing attention to meet the carbon-neutral requirements. In this work, DMM oxidation was studied by using a novel supercritical pressure jet-stirred reactor at 10 and 100 atm, with temperatures between 450 and 950 K, and equivalence ratios of 0.27 and 2.0. The experimental results show that the negative temperature coefficient (NTC) behavior becomes much weaker under 100 atm than the case of 10 atm. One reason is the significant shift of the intermediate-temperature HO₂ chemistry to lower temperature at 100 atm and the other one is the increase of multi-oxygen addition reactions at 100 atm. Selected kinetic models in the literature show some discrepancies in comparison to the experimental results in this study. Thus, a new model updated from a previous study was developed to improve the prediction of the experimental data under high pressures. Reaction pathway and sensitivity analyses were performed to identify key reactions in DMM high-pressure oxidation. DMM H-atom abstraction at the primary C site by OH (DMM_1 radical) is found to be the most important reaction to promote oxidation, while the secondary site (DMM_2 radical) shows different sensitivity under different conditions. The reason is that under richer or lower pressure conditions, the decomposition of DMM_2 is favored over O₂ addition, thus inhibits the oxidation process. DMM H-atom abstractions by CH₃O and HO₂ are found to be important under low- and intermediate-temperature, respectively. Therefore, more efforts in studying these reactions are suggested to further improve the model prediction. In addition, reaction 2HO₂ = 2OH + O₂, added in this work, is found to be important in promoting DMM oxidation at the early stage and improves model prediction on oxidation onset temperature.