The mitigation of nitrogen oxide ( \(\textrm{NO}_x\) ) emissions remains a key challenge for the use of ammonia as a carbon-free energy carrier. In contrast to hydrogen, ammonia combustion is inherently prone to fuel- \(\textrm{NO}_x\) formation due to the nitrogen content of the fuel, limiting the effectiveness of purely temperature-based mitigation strategies. In this work, liquid water addition is investigated as a potential emission control approach for premixed ammonia/air flames using high-fidelity numerical simulations. A hybrid Eulerian–Lagrangian framework is employed to resolve the interaction between a spherically expanding quasi-laminar ammonia flame and evaporating water droplets. The influence of droplet sizes on flame propagation, flame thickness, and emission behavior is examined under stoichiometric conditions. Water addition is found to reduce the burning rate per unit area and increase flame thickness through combined thermal and dilution effects, while having a limited impact on flame surface wrinkling. Both small and large droplets lead to a significant reduction in NO formation, with large droplets producing localized regions of strong suppression and small droplets yielding a more spatially uniform reduction. Analysis of intermediate nitrogen species indicates a minor contribution of the \(\textrm{N}_{2}\textrm{O}\) pathway under the present conditions, while thermal and fuel- \(\textrm{NO}_x\) pathways remain sensitive to water-induced temperature changes. These results provide physical insight into the coupling between water evaporation, flame structure, and \(\textrm{NO}_x\) formation in premixed ammonia flames.
