Kinetic interactions in NH3+H2+H2O oxidation: Broad-range shock tube ȮH laser diagnostics and modeling

Co-firing low-reactivity NH 3 with H 2 enhances its practical utility, while steam injection mitigates H 2 -induced reactivity overshoot and suppresses NO x emissions. Given steam's abundance in exhaust streams and its recirculation potential, understanding high-temperature H 2 O-fuel interactions is critical. This study employs reflected shock waves with UV laser absorption spectroscopy to measure in situ ȮH radical time-histories during NH 3 /H 2 /H 2 O/O 2 /Ar oxidation at pressures of 1.5–15.5 atm, temperatures of 1566–2485 K with variable H 2 blending and H 2 O addition ratios. Thirteen kinetic models were evaluated against measurements using error function analysis. The Mei-2019 model showed minimal overall error yet exhibited notable deviation in ȮH-ignition delay times (IDTs) and profile shapes. The model was refined by updating rate constants of 16 ȮH-sensitive reactions, informed by critical reassessment of experimental and theoretical literature. Virtual additive analysis revealed that under low-enthalpy-change conditions, both H 2 and H 2 O primarily influence OH kinetics via direct chemical participation, not third-body collision or thermal effects. Higher H 2 fraction intensify H 2 -related pathways, expanding H/ȮH/Ö radical pools and accelerating NH 3 consumption via Ḣ-abstraction. Pathway-specific interrogation further identified key H 2 O-involved reactions governing hydrogen-rich ammonia combustion: H 2 + ȮH = Ḣ + H 2 O, NH 3 + ȮH = NH 2 + H 2 O, Ö + H 2 O = 2ȮH. • First high-pressure ȮH profiles (≤15.5 atm) under NH 3 /H 2 /H 2 O interactions. • Systematic deficiencies in OH prediction revealed via kinetic model evaluation. • Model refinement via updated rate constants for 16 ȮH-sensitive reactions through critical reassessment. • Virtual additive analysis decouples thermodynamic/kinetic effects of H 2 and H 2 O.