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

摘要

Ammonia (NH_(3)) is considered a promising carbon-neutral fuel, with a high hydrogen content, that can diversify the global energy system. Blending ammonia with a highly reactive fuel is one possible strategy to enhance its combustion characteristics. Here, an investigation of blends of NH_(3) and dimethoxymethane (DMM), a biofuel with high fuel-born oxygen content and no carbon–carbon bonds, is reported. Unstretched laminar burning velocity (iS _(L)) and Markstein length of different NH_(3)/DMM blends were experimentally determined using spherically propagating premixed flames. The DMM mole fraction was varied from 0.2 to 0.6 while measuring iS _(L) at 298 K, 0.1 MPa, and equivalence ratios (Φ) over the range of 0.8–1.3. The addition of DMM was found to immensely enhance the combustion characteristics of ammonia. DMM 20% (by mole fraction) in the NH_(3)/DMM blend increased iS _(L) by more than a factor of 3 over neat ammonia; such enhancement was found to be comparable to 60% CH_(4) in NH_(3) (Φ = 0.9–1.1) blends. Increasing Φ was found to significantly decrease the burned gas Markstein length for lean cases, whereas a negligible effect was observed for rich mixtures. A composite chemical kinetic model of DMM/NH_(3), aimed at interpreting the high-temperature combustion chemistry, was able to reliably predict iS _(L) for neat NH_(3) and DMM flames. Also, the predictive capability of the kinetic model to describe iS _(L) for DMM/NH_(3) blends is reasonably good. Sensitivity analysis and reaction path analysis indicated that the NH_(3)/DMM blends could be understood as dual oxidation processes of the individual fuels that are competing for the same radical pool.