Non-premixed combustion and NOX 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 (NOX) 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 NOX 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.