Numerical investigation of synergistic effects of nanopulsed plasma and water addition on hydrogen combustion and NO emissions

This study presents a novel integrated approach using nanopulsed repetitively pulsed discharge (NRPD) plasma with H 2 /H 2 O/Air mixtures to overcome high NO emissions and ignition delay timing (IDT) in hydrogen combustion, utilizing zero-dimensional ChemPlasKin simulations and Design of Experiments (DoE). A key finding is that while water vapor inhibits conventional autoignition, plasma-assisted ignition (PAI) is insensitive to water, as plasma dissociates H 2 O into reactive radicals (H, O, OH), effectively turning water into an ignition promoter and enhancing early radical formation. PAI achieves significantly lower flame temperatures (12.3 % reduction) and approximately 58 % lower NO emissions compared to conventional autoignition through non-thermal chemical pathways. Comparative analysis quantified that plasma kinetic effects play a dominant role in reducing IDT, contributing substantially more to enhancement than plasma thermal effects alone. Furthermore, the sensitivity analysis of NO formation revealed that water vapor significantly alters the kinetics of NO-related reactions, changing the sensitivity and role of key pathways like H + NO 2 ⇌ NO + OH, suggesting water can reverse certain reactions from producing NO to consuming it. This plasma-water synergy successfully broadens and stabilizes low-NO combustion regimes. • Plasma–water synergy cuts NO x emissions by up to 58 % vs autoignition. • NRPD plasma offsets water's inhibition, cutting ignition delay. • Plasma lowers flame temperature ∼12.3 %, limiting thermal NO x . • Water generates radicals (H, O, OH) in plasma, boosting ignition. • DoE optimization conditions for stable, low-NO x hydrogen combustion.