LARGE EDDY SIMULATION OF AMMONIA-HYDROGEN NON-PREMIXED FLAMES STABILIZED ON A BLUFF BODY BURNER

The demand for carbon-free fuels such as ammonia (NH₃) and hydrogen (H₂) has been growing rapidly due to stricter environmental policies on carbon emissions. Since ammonia is easier to store and transport, it is considered the leading alternative fuel for marine, aviation, and gas turbine industries. However, the narrow flammability, low reactivity, and potential emissions of nitrogen oxides (NO_x) are important challenges that need to be overcome if ammonia is to be used as a practical fuel for industrial use. Recent works have provided important experimental data on the characteristics of NH₃ flames under premixed and non-premixed combustion modes, focusing on flame speed, turbulence-chemistry interaction, and especially the dissociation/cracking of NH₃ into H₂ and N₂. These measurements have encouraged the use of Computational Fluid Dynamics (CFD) for the simulation and scaling of practical ammonia systems, evaluating the performance of different numerical models for NH₃ combustion. In this study, Large Eddy Simulation (LES) is utilized to predict a series of NH₃/H₂/N₂ non-premixed flames stabilized on a bluff body burner. The accuracy of the Flamelet Generated Manifold (FGM) combustion model combined with LES has been examined, using a commercial CFD solver. The different cracking levels of NH₃ into H₂ and N₂ lead to simulation cases ranging from an H₂/N₂ flame (i.e., “fully cracked”), to a flame with 50% NH₃ (i.e., “half cracked”). The different flame shapes, temperature distributions, NO_x and unburnt NH₃ emissions have all been simulated, generally matching well the available experimental data. The developed model settings and numerical workflows may be applied to simulating more complex combustors which use NH₃ as a fuel.