Experimental and Modeling Evaluation of Dimethoxymethane as an Additive for High-Pressure Acetylene Oxidation

The high-pressure oxidation of acetylene-dimethoxymethane (C₂H₂-DMM) mixtures in a tubular flow reactor has been analyzed from both experimental and modeling perspectives. In addition to pressure (20, 40, and 60 bar), the influence of the oxygen availability (by modifying the air excess ratio, λ) and the presence of DMM (two different concentrations have been tested, 70 and 280 ppm, for a given concentration of C₂H₂ of 700 ppm) have also been analyzed. The chemical kinetic mechanism, progressively built by our research group in the last years, has been updated with recent theoretical calculations for DMM and validated against the present results and literature data. Results indicate that, under fuel-lean conditions, adding DMM enhances C₂H₂ reactivity by increased radical production through DMM chain branching pathways, more evident for the higher concentration of DMM. H-abstraction reactions with OH radicals as the main abstracting species to form dimethoxymethyl (CH₃OCHOCH₃) and methoxymethoxymethyl (CH₃OCH₂OCH₂) radicals are the main DMM consumption routes, with the first one being slightly favored. There is a competition between β-scission and O₂-addition reactions in the consumption of both radicals that depends on the oxygen availability. As the O₂ concentration in the reactant mixture is increased, the O₂-addition reactions become more relevant. The effect of the addition of several oxygenates, such as ethanol, dimethyl ether (DME), or DMM, on C₂H₂ high-pressure oxidation has been compared. Results indicate that ethanol has almost no effect, whereas the addition of an ether, DME or DMM, shifts the conversion of C₂H₂ to lower temperatures.