Large-Eddy Simulation of a Non-Premixed Ammonia-Hydrogen Flame: NOx emission and Flame Characteristics Validation

The interest in ammonia and ammonia-hydrogen combustion as fuel for Gas Turbine (GT) applications implies the resolution of many technical challenges. The prediction of their flame characteristics, like flame morphology and pollutant emissions, through numerical simulations and specifically through Computational Fluid Dynamics (CFD) is one of them. In terms of NOx and unburnt emissions, the main roadblock is often related to a wide discrepancy of the results changing the employed chemistry set. In the present work a non-premixed ammonia-hydrogen flame is investigated numerically and compared with the experimental findings retrieved in a test condition of the atmospheric pressure test campaign presented by Pugh et al. [1]. The CFD simulation is based on the species transport model with a different closure of the chemical source term depending on the cell-based combustion regime. The numerical case is based on a skeletal mechanism retrieved ad hoc to optimize the computational effort and preserve the main species needed for the calculation of the NOx emission. A detailed assessment of the CFD calculated NOx is carried out comparing it with experimental data. Following that a Chemical Reactor Network (CRN) model is used for NOx evaluation leveraging the time-averaged numerical solution from CFD. Some of the most accurate detailed chemical mechanisms present in literature are tested using the CRN model. The results from CFD and CRN reveal that there is a need to improve the pollutant emission for ammonia-hydrogen flame operating under lean non-premixed conditions.