An Experimental and Kinetic Modeling Study of Laminar Flame Speed of Dimethoxymethane and Ammonia Blends

Abstract

Ammonia (NH3) is considered a promising carbon-neutral fuel, with high hydrogen content, that can diversify the global energy system. Blending ammonia with a highly reactive fuel is one possible strategy to enhance it’s combustion characteristics. Here, an investigation of blends of NH3 and dimethoxymethane (DMM), a biofuel with high fuel-born oxygen content and no carbon-carbon bonds, is reported. Unstretched laminar burning velocity (SL) and Markstein length of different NH3/DMM blends were experimentally determined using spherically propagating premixed flames. The DMM mole fraction was varied from 0.2 to 0.6 while measuring SL at 298 K, 0.1 MPa and equivalence ratios () over a range of 0.8 to 1.3. The addition of DMM was found to immensely enhanced the combustion characteristics of ammonia. DMM 20% in NH3/DMM blend increased SL more than a factor of 3 over neat ammonia; such enhancement was found to be comparable with 60% CH4 in NH3 ( = 0.9 -1.1) blends. Increasing  was found to significantly decrease the burned gas Markestein length for lean cases, whereas a negligible effect was observed for rich mixtures. A composite chemical kinetic model of DMM/NH3, aimed at interpreting the high-temperature combustion chemistry, was able to reliably predict SL for neat NH3 and DMM flames. Also, the predictive capability of the kinetic model to describe SL for DMM/NH3 blends is reasonably good. Sensitivity analysis and reaction paths analysis indicated that the NH3/DMM blends could be understood as the dual oxidation processes of the individual fuels which are competing for the same radical pool.