On the distribution of NO and N2O within the flame front in premixed turbulent combustion of lean NH3-air and NH3/H2/N2-air mixtures
Combustion and Flame, cilt.295, 2027 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 295
- Basım Tarihi: 2027
- Doi Numarası: 10.1016/j.combustflame.2026.115349
- Dergi Adı: Combustion and Flame
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Chimica, Compendex, EMBASE, Environment Index, INSPEC, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
- Anahtar Kelimeler: Direct numerical simulation (DNS), Lean premixed NH₃/H₂ flames, NO and N₂O formation, Preferential diffusion, Radical chemistry
- Bilecik Şeyh Edebali Üniversitesi Adresli: Evet
Özet
The coupled effects of radical chemistry, preferential diffusion, flame curvature, and local mixture inhomogeneity on NO and N₂O distribution in lean turbulent premixed NH₃/H₂ flames are investigated using direct numerical simulation (DNS). Statistically planar NH₃–air, 60%NH₃/25%H₂/15%N₂–air, and 40%NH₃/45%H₂/15%N₂–air flames at an equivalence ratio of 0.81 are considered, all operating in the thin reaction zones regime at comparable conditions on the Borghi–Peters diagram. NO concentration increases monotonically with H₂ blending, despite similar burned gas temperatures, due to enhanced H, O, and OH radical availability that accelerates NH₃ decomposition, promotes fuel-N oxidation pathways (NH → NO and HNO → NO), and shifts NO formation towards earlier flame stages, thereby limiting NO reduction. As a result, the ratio of the volume-integrated NO mass to the volume-integrated total mass in the flame increases systematically with H₂ addition. In contrast, the increase in the ratio of the volume-integrated N2O mass to the volume-integrated total mass within the flame seems to exhibit a tendency towards saturation. Statistical correlations reveal a transition from formation- to destruction-controlled N₂O chemistry, with preferential diffusion effects becoming increasingly important at higher H₂ blending. These results demonstrate that nitrogen oxide emissions in NH₃/H₂/N2 flames are governed by coupled chemistry–transport interactions rather than temperature alone, with important implications for emission mitigation strategies. Novelty and significance statement: This work provides a DNS-based mechanistic assessment of NO and N₂O formation in lean turbulent premixed NH₃ and NH₃/H₂/N2 flames under comparable thermal conditions and identical turbulence–chemistry interaction regimes. It is shown that the monotonic increase in NO formation with H₂ blending is not governed by flame temperature but by enhanced radical production and preferential diffusion, which accelerate NH₃ decomposition and shift fuel-N oxidation toward earlier flame stages. In contrast, N₂O formation exhibits a saturation with H₂ blending. Correlation analyses further reveal the increasing influence of flame curvature and local mixture inhomogeneity on nitrogen chemistry with H₂ addition. These findings provide new insight for emission control in ammonia-fuelled combustion.