Rich-Quench-Lean model comparison for the clean use of humidified ammonia/hydrogen combustion systems

Ammonia and hydrogen are examples of zero-carbon fuels of high interest for implementation in gas turbine technologies. However, large emissions of nitrogen oxides are still a major detrimental for the implementation of these technologies. Therefore, various techniques have been presented as potential solutions to mitigate this problem. Rich-Quench-Lean systems combined with humidified atmospheres are amongst the most promising with the reduction of emissions as a consequence of recombinations of species and lower combustion temperatures. However, limited scrutiny exists around the chemical progression of species in systems like these whilst being fuelled with ammonia blends. Furthermore, any chemical study currently faces a challenge for the selection of a chemical kinetic mechanism due to the great variety of available mechanisms for ammonia combustion, each with different characteristics for the resolution of this fuel. Thus, a Chemical Reactor Network (CRN) has been developed to numerically assess an industry scale humidified Rich-Quench Lean system, utilising five of the most used chemical kinetic models in humidified ammonia combustion whilst informing developers of the differences between those selected. The results displayed significant differences between the mechanisms as the flame progresses. Sensitivity analyses of [OH] and [NH3] displayed similar reactions having opposing effects for these two species at various points of the burner. Quantitative Reaction Path Diagrams (QRDP) for NO showed both similarities and differences between the mechanisms in terms of paths taken and rates of production.