Large eddy simulations of ammonia combustion and development of reduced chemical kinetics

Ammonia is a promising carbon-free fuel for future energy systems, but its practical implementation is challenged by low laminar flame speeds and elevated NO x emissions. Computational fluid dynamics (CFD) provides a powerful tool for analysing ammonia combustion systems; however, the high computational cost associated with detailed chemical kinetics remains a key limitation for industrial-scale applications. In this study, a Large Eddy Simulation (LES) framework is developed for a 4.6 kW ammonia burner and validated against axial velocity and OH measurements, demonstrating good agreement with experimental data. Building on a recent ammonia reaction mechanism, a reduced mechanism consisting of 17 species and 79 reactions is derived and implemented in the CFD framework. The reduced mechanism decreases the computational cost from 11,000 to 6279 core-hours/s relative to the original mechanism, and by approximately 10% compared to an alternative reduced mechanism, while retaining accuracy in flame structure, OH fields, and axial velocity. At the same time, the reduced mechanism preserves higher NO predictions characteristic of the original mechanism and captures NH 3 decomposition into H 2 , which is relevant for flame stabilisation in the burner. These results highlight the potential of targeted mechanism reduction for achieving cost-efficient CFD modelling of ammonia combustion, thereby supporting future industrial-scale modelling and the adoption of ammonia as an energy carrier.