Medium speed lean hydrogen engine modelling and validation

Hydrogen spark-ignition direct-injection engines result in no carbon emissions at use, but NO X remains a challenge. This study demonstrates that with lean combustion (ϕ < 0.38), in-cylinder NO X can be reduced to a quarter of the current maritime regulatory limit. An original contribution of this work is the use of species-resolved emissions formation across multiple engine load conditions. A novel, chemically detailed combustion modelling framework was developed in CHEMKIN-Pro, incorporating the evolution of the CRECK C1–C3 NO X mechanism, for improved high-pressure accuracy. The framework was extensively validated using crank-angle-resolved data across 9–18 bar loads. The model accurately reproduced pressure traces, heat release angles, and NO X . Mechanistic analysis revealed a shift from thermal Zeldovich NO X to intermediate-species (notably N 2 O-driven), as equivalence ratio and pressure varied. The findings highlighted the use of a high-fidelity chemical kinetic modelling framework, not only to match experimental results, but to gain physically grounded insight into actionable near-zero emission strategies. • Developed validated CHEMKIN-Pro medium speed hydrogen engine modelling framework. • Experimental lean engine combustion (ϕ < 0.38) results across 9–18 bar loads. • High engine indicated thermal efficiencies of 45–50 % with stable combustion. • Novel mechanistic NO x insight, revealing thermal-to-intermediate transitions. • In-cylinder NO x remained below 1/4th of the maritime Tier III emissions.