Non-premixed combustion and NO_X emission characteristics in a micro gas turbine swirl combustor fueled by methane and ammonia at various heat loads

In comparison to methane (CH₄), ammonia (NH₃) is considered a potential carbon-free alternative fuel that can reduce greenhouse gas emissions. But a principal concern is the generation of elevated nitrogen oxide (NO_X) emissions from NH₃ flame. In this study, the detailed reaction mechanisms and thermodynamic data of CH₄ oxidation and NH₃ oxidation were performed using the steady and unsteady flamelet models. After validation of the turbulence model, the combustion and NO_X emission characteristics of CH₄/air and NH₃/air non-premixed flames in a micro gas turbine swirl combustor under a series of identical heat loads were numerically investigated and compared. The present results show that the high-temperature zone of the NH₃/air flame migrates more rapidly toward the outlet of the combustion chamber than that of the CH₄/air flame as the heat load increases. The average NO, N₂O, and NO₂ emission concentrations at all heat loads from NH₃/air flame are respectively 6.12, 161.05 (given the very low N₂O emission concentration from CH₄/air flame), and 2.89 times higher than those from CH₄/air flame. There are correlation trends between some parameters (e.g. characteristic temperature and OH emissions) with the variation of the heat load, and the relevant parameters can be tracked to predict the emission trends after changing the heat load.