Development and validation of a retuning-free skeletal mechanism for NH3/H2/Air combustion

This work develops and validates a retuning-free 23-species skeletal mechanism for NH 3 /H 2 /air combustion, from the high-fidelity, first-principles-informed 53-species Kao et al. parent mechanism (Kao et al., 2026), without empirical modification of the retained kinetic or thermochemical parameters. The resulting mechanism was systematically evaluated against ignition delay times, laminar burning velocities, jet-stirred reactor species profiles, plug flow reactor species evolution, extinction strain rates, and turbulent computational-fluid-dynamics (CFD) fidelity tests. Elevated-pressure ignition cases up to 60 bar outside the reduction domain were used as extrapolative validation. The validation strategy separates parent-to-reduced fidelity from agreement with experiments and from benchmarking against literature mechanisms. Across the canonical validation configurations, the reduced mechanism closely follows the parent mechanism, indicating that the dominant ignition, flame-propagation, intermediate-species, and NO x -formation responses of the parent chemistry are retained. Relative to representative literature benchmark mechanisms, the present mechanism provides consistently balanced performance over pure NH 3 and NH 3 /H 2 conditions, while avoiding the empirical retuning commonly used in compact ammonia-fuel chemistry. In a RANS/EDC CFD simulation of a turbulent partially premixed NH 3 /H 2 /N 2 –air jet flame, the reduced mechanism reproduces the parent-mechanism predictions of temperature, NH, NO, and N 2 O profiles with substantially reduced computational cost under the present solver settings. The resulting mechanism provides a compact, retuning-free, CFD-practical chemistry model for predictive simulations of NH 3 /H 2 combustion within the validation ranges documented in this work, while its main parent-inherited limitations are observed for rich pure-NH 3 ignition at 30 atm and for NO prediction in the high-H 2 JSR and 50/50 NH 3 /H 2 PFR cases. Novelty and significance statement This work reports a new retuning-free skeletal mechanism for NH 3 /H 2 /air combustion obtained from the recently developed Kao et al. parent mechanism (Kao et al., 2026). The mechanism is constructed using an established DRGEP–DRG–FSSA workflow without post-reduction parameter tuning, accompanied by same-parent workflow controls and a validation suite spanning ignition, flame propagation, reactor speciation, extinction, and CFD-relevant calculations. The study thereby documents the mechanism’s parent-to-reduced fidelity, extrapolative behavior, computational benefit, and remaining parent-inherited limitations.