Stability and NOx Emissions of Oxy-Ammonia Swirl Premixed Flames in an Emissions-Controlled Gas Turbine Combustor

Abstract This study provides a design-relevant numerical analysis of ammonia–oxygen (NH3/O2) combustion, focusing on the effects of inlet preheating (298–520 K), equivalence ratio (φ = 0.7–1.2), and bulk flow velocity (5.2–12 m/s) on flame stability and NOx formation. The simulations reveal that preheating improves flame compactness and stabilization, raising maximum flame temperature by only ~30 K (2830→2860 K) but accelerating chemical kinetics. Equivalence ratio is the dominant flame parameter: lean conditions (φ = 0.9) produce the highest flame temperatures (2860 K), while moderately rich conditions (φ =1.2) suppress NO by 86% (9000 → 1250 ppm) due to OH depletion (45% drop) and enhanced H2 generation (0.015→0.10 mole fraction). Flow velocity strongly influences aerodynamics and flame stability: low velocity (5.2 m/s) generates weak recirculation, high velocity (12 m/s) elongates and destabilizes the flame, whereas intermediate velocities (7–9 m/s) establish coherent recirculation zones that ensure robust anchoring. NOx emissions remain essentially invariant across the velocity range (3846 ppm), with NO2 and N2O negligible, confirming that inlet velocity affects stability but not equilibrium pollutant levels. The findings offer actionable insights into the design of low-NOx, carbon-free ammonia gas turbine systems.