Sensitizing and inhibiting effects of nitrogen oxides in dimethoxymethane oxidation: Experiments and kinetic modeling

Dimethoxymethane (DMM, or OME1) has recently raised significant attention as the archetypal species of the oxymethylene ethers (OME) family, identified as a potential sustainable alternative to diesel fuels. However, so far limited attention has been paid to the sensitizing and inhibiting effects of nitrogen oxides (NOx) on its oxidation chemistry, which may play an important role for combustion with exhaust gas recirculation (EGR) systems. In this work, DMM oxidation was systematically studied with and without NO addition through a targeted experimental campaign. Four fuel-oxidizer mixtures were analyzed in a laminar flow reactor, across a range of variable equivalence ratios (0.8 ≤ Φ ≤ 2), argon dilution levels (93% and 97%) and NO concentrations (0 and 900 ppm). At the same time, a comprehensive kinetic mechanism was set up, including carbon–nitrogen interactions up to the fuel-NO level. It was found that the dilution level significantly affected the DMM/NO interaction. While the onset temperature of the DMM conversion remained unchanged for a fixed dilution, the addition of NO led to a faster completion of the DMM conversion. The kinetic analysis clarified that the earlier reactivity of DMM at lower dilution triggers C-N interaction both at the fuel level, through the NO-alkoxy reaction inhibiting the low-temperature oxidation, and at a C0-C1 level, via the enhanced formation of CH3O, promoting an earlier reactivity (as observed for simpler fuels). Conversely, when the reactivity onset shifted to higher temperatures because of the higher dilution, the interaction was much less emphasized at the fuel level, but mostly controlled by CH3O formation and consumption channels.