Water-moderated combustion and NOx emissions in ammonia/hydrogen blends: Detailed kinetics with supporting data-driven correlations

Ammonia combustion is offset by long ignition delays, low burning velocities, and high NO x . This study probes H 2 enrichment and H 2 O addition to jointly tune reactivity and emissions, assessing effects on ignition delay time (IDT), laminar burning velocity (LBV), flame thickness, heat release rate (HRR), and NO/N 2 O. Using validated 0D/1D simulations plus sensitivity and pathway analyses, and data-driven surrogates (polynomial-Lasso, HGB), we achieve reduced-order models with R 2 : IDT 0.999, LBV 0.997, NO 0.981, N 2 O 0.972. H 2 markedly shortens IDT; a blend with 20% H 2 and 20% H 2 O highlights synergy via coupled dissociation. H 2 O suppresses LBV, flame thickness, and HRR through thermal/dilution effects, while lowering NO x by cooling and promoting NO reduction (NH 2 + NO → NNH + OH; NH 2 + NO → H 2 O + N 2 ) and N 2 formation via N 2 H 2 /N 2 H. Sensitivity shows H 2 boosts LBV via H + O 2 ⇌ O + OH; H 2 O moderate via H + O 2 (+M) ⇌ HO 2 (+M). • Synergistic H 2 /H 2 O effects on NH 3 IDT, LBV, Flame thickness, HRR, and NO x . • H 2 boosts NH 3 ​ flame speed; H 2 ​O consistently suppresses LBV due to thermal effects. • Optimized NH 3 ​/H 2 ​/H 2 ​O blends balance reactivity with H 2 O moderation for low NO x . • Detailed kinetics and sensitivity clarify key NH x –NO x reaction pathways with H 2 /H 2 O. • Machine learning surrogates predict IDT, LBV, NO, N 2 O with R 2 ≥ 0.97.