The Influence of Turbulence Intensity on NOx Emission and Flame Topology in Ammonia/Air Premixed Combustion

Abstract This research investigates the effects of turbulence on NOx formation and flame topology in ammonia/air premixed combustion through Direct Numerical Simulations (DNS). The DNS was conducted using PeleLM, an adaptive mesh hydrodynamics simulation solver for low Mach number reacting flows. The ammonia/air premixed flame simulations under an equivalence ratio of 1.2 were performed on 6 turbulence intensities of u’/SL = 6.7–40.8 whose Karlovitz numbers are 9.5–142.7. The results indicate that increasing turbulence leads to significant flame front wrinkling and distortion, producing high-curvature regions. NOx formation is preferentially enhanced in localized negative curvature regions, primarily due to increased local temperatures and elevated O2 fraction. In contrast, positive curvature regions exhibit lower NO concentrations, which are associated with increased strain effects and reduced O2 availability. With enhanced reactivity in high-curvature zones and subsequent NOx stabilization due to turbulence-induced dilution effects, this interplay results in a characteristic NOx evolution pattern, where local peaks near the flame front contrast with an eventual stabilization in the far downstream, bringing global NOx concentrations closer to laminar levels.