Emission prediction and analysis on CH4/NH3/air swirl flames with LES-FGM method

Ammonia, made up of 17.8% hydrogen, is one of carbon free fuels which can be used in large-scale power plants. However, ammonia combustion faces some challenges due to the high NOx emission. This study investigates the emission characteristics of CH4/NH3/air co-firing premixed swirling flames with NH3 mole fraction up to 60% in a model combustor. Large eddy simulation (LES) coupled with flamelet generated manifold (FGM) model which considers the transport equations of slow chemical emission component was performed, with experimental validation in both flame structure and global emission. The simulation shows an overall good agreement with experimental results. It is found that the NO emission is improved with the NO transport equation calculated during the simulation. The results imply that the nitrogenous components, residence time and temperature are important factors that influence NO concentration profile. The residence time of inner recirculation indicates the NO level for CH4/NH3/air flames, and local high NO concentration is mainly caused by local long residence time. The OH and NO are correlative in premixed CH4/NH3/air flames because these components are both strongly related to the temperature. N2O has a correlation with NH and HNO components. The radical components such as HNO, O, OH etc. also influence the emission formation process. When the NH3 ratio is closed to 40%, the concentration of H, OH, O2 and HNO are all adequate to produce maximum NO.

Automated summary

This study investigates the emission characteristics of CH4/NH3/air co-firing premixed swirling flames, using a model combustor and Large Eddy Simulation (LES) coupled with flamelet generated manifold (FGM) model. The results show that the addition of ammonia can improve NO emissions, while factors such as residence time and temperature also play important roles in NO concentration profile.