Extension of the dynamic Thickened Flame model for partially-premixed multi-fuel multi-injection combustion and application to an ammonia–hydrogen swirled flame

An extension of the widely-used Thickened Flame model for Large Eddy Simulations (TFLES) is proposed to take into account multi-fuel multi-injection combustion processes. Indeed, in such systems the local variations of the fuel composition and the local evolution of the equivalence ratio issued by differential diffusion effects inferred by the potential different nature of the used fuels need to be addressed for a proper use of the standard TFLES model. To do so, the extended model relies on a description of the differentiated fuel injections mixing that is computed from a transported mixture fraction tracing the spatial evolution of each fuel stream. This allows to both incorporate local fuel composition inhomogeneities into the combustion model and a proper parameterization of the flame sensor or turbulent combustion model. The proposed modeling is then used to predict the ammonia–air swirling flame stabilized by multiple hydrogen injection holes and operated at Cardiff University. To perform this specific simulations, a dedicated and novel analytically reduced chemical kinetics model for NH3-H2-N2/air combustion is also derived and validated at gas turbine operating conditions and for multiple ammonia–hydrogen binary fuel blends as well as ternary fuel blends derived from ammonia decomposition. The results obtained by the use of the novel Multi-Fuel TFLES model (MF-TFLES) are compared against the conventional TFLES predictions and assessed via OH* chemiluminescence and NO Planar Laser Induced Fluorescence (NO-PLIF) experimental data. As shown, the proposed modeling improves the flame shape and structure prediction by assuring the correct local application of the artificial flame thickening coherently, taking into consideration the multi-fuel complex mixing process, a feature that the standard TFLES model cannot consider hindering the quality of the prediction. Novelty and significance statement The novelty of this research can be summarized in two statements: 1. Extension of the widely used TFLES turbulent combustion model to consider flames where differential diffusion is present, as well as, partially-premixed multi-fuel multi-injection problems. 2. A novel NH3-H2-N2 analytically reduced chemistry suited for reactive LES. This work is significant because it allows to simulate unconventional burner setups which are being explored for decarbonized fuels, such as NH3 and the highly diffusive H2, in an effort to reduce the impact of power generation on climate change. Furthermore, high-fidelity modeling, such as the approach presented in this study, will allow the scientific community to understand the pollutant production of decarbonized fuels in the gas turbines context, thereby contributing to the development of adapted technological solutions towards carbon-free power generation solutions.