High-Pressure Oxidation of Ammonia Mixed with Dimethoxymethane

The oxidation of ammonia-dimethoxymethane (NH₃-DMM) mixtures at high pressure was analyzed from both experimental and kinetic modeling points of view. Experiments were performed using a laboratory tubular flow reactor installation and were conducted at 10, 20, and 40 bar under fuel-rich (λ = 0.7), stoichiometric (λ = 1), and fuel-lean (λ = 3) conditions and temperatures ranging from 650 to 1250 K. The inlet DMM concentration was varied (100 and 200 ppm), keeping the concentration of ammonia constant at 1000 ppm. The data were interpreted in terms of a detailed chemical kinetic model. Despite some discrepancy between the model predictions and measurements, the model accurately followed the experimental trends, highlighting its ability to describe the oxidation of the NH₃-DMM mixture. The experimental and predicted results suggested that the conversion of both ammonia and DMM was favored by increased pressure and higher inlet concentrations of O₂ and DMM. Under the conditions of the present work, the dominant path for ammonia and DMM conversion leads to N₂/N₂O and CO/CO₂ in any case. Concentrations of NO and NO₂ were below the detection limit in all the experimental conditions studied, which imply a benefit in the reduction of NO _x emissions during the combustion of pure ammonia. DMM enhanced the ammonia reactivity, although its presence leads to the formation of CO₂ not only by the common CO + OH reaction but also through the interaction of N₂O with CO.