Numerical investigation of NOx emission characteristics in air-staged combustion system fueled by premixed ammonia/methane

For the purpose of achieving global CO2 reduction, decarbonization at the source of fuels is a practical approach. The transition phase of blending fossil fuels with carbon-free fuels for combustion is a hot topic in the current carbon emission reduction process. In order to achieve efficient and low-pollution combustion of NH3/CH4, the combustion and emission characteristics of NH3/CH4 under single-stage and air-staged combustion methods were numerically investigated in this work. The emissions were compared for different equivalence ratios and different ammonia content conditions. Rate of production (ROP) and sensitivity analysis were performed for NOx, and the reaction path of NH3/CH4 was analyzed. The results indicate that the C-N interaction of the NH3/CH4 mixed combustion process is not significant and turns weaker in the lean flames. HNO intermediate is an important specie for NO generation, and HCN together with HCO intermediate, are essential species for CO generation. NH2 and NH almost dominate the promotion and inhibition of NO generation. Given the contrasting NOx and CO emission behavior of NH3/CH4 in rich and lean flames, the single-stage combustion approach is not suitable. Air-staged combustion achieves both, ensuring the complete burning of NH3 and CH4 while reducing NOx and CO emissions. Moreover, the results suggest that Φpri = 1.2/Φtotal = 0.6 is the optimal NH3/CH4 combustion staging method for controlling NOx emissions. •A chemical reactor network model for the swirl blending combustion of NH3/CH4 is constructed.•Emission characteristics of ammonia-based fuels in single and air-staged combustion.•Rate of production and sensitivity analysis are conducted to identify species' importance.•Combustion reaction path analysis is carried out to reveal the conversion relationship.