Enhancing and assessing ammonia-air combustion performance by blending with dimethyl ether

As a hydrogen energy carrier and carbon-free fuel, ammonia (NH3) is being growingly considered as an alternative fuel for combustion systems in an effort to reduce carbon emissions. Unlike conventional fossil fuels, its relatively low flame speed hinders its widespread use in practice. Utilizing the 1D freely propagating flame model in Chemkin-Pro 2019, this work numerically evaluates the impact of blending ammonia with dimethyl ether (DME) on the laminar burning velocity of NH3/air flames. For this, the reaction mechanism is first validated by comparing predictions to experimental data available in the literature. The addition of DME is found to significantly enhance the laminar burning velocity (SL) of NH3 flames, which can be comparable to that of hydrocarbon fuels. This enhancement is a result of the combined thermal and chemical effects. Reaction pathway and sensitivity analyses reveal that adding DME enables the major reaction steps and the sensitivities to be altered, thus positively affecting the overall reaction rate. Furthermore, the SL of NH3/air flames is weakly dependent on the inlet thermodynamic pressure, but becomes stronger with more DME blended. The explanation behind this phenomenon is that the relative importance of the termination versus branching reactions is more significant in binary flames. The overall reaction order characterizing the importance of the chain branching and the terminating reactions shows a decreasing trend with increasing inlet pressure. In general, the present work provides a design guideline on the selection of fuel flexibility and sheds light on the fundamental NH3-DME-fueled flame enhancement mechanisms.