Investigation of NOx formation and emission control for rich-quenching-lean combustion strategy burning ammonia

This study investigated the rich-quenching-lean (RQL) strategy’s combustion process, focusing on fuel-bound nitrogen migration. A chemical reactor network model with ammonia reaction kinetics was utilized to predict chemical behavior. The ammonia is primarily converted to N 2 in the rich zone within a sufficient residence time. The theoretical analysis and numerical results show that the flow affects ammonia consumption in the rich zone. Amid turbulence, the ammonia residual decreases linearly with increasing residence time. In a plug flow, the unburned ammonia concentration decreases exponentially along the axial coordinate. A numerical experiment was conducted over a large parameter space to explore the RQL combustion strategy’s limits on NOx emissions performance, showing that the rich zone equivalence and ammonia cracking ratios govern the minimum achievable NOx emissions. Moreover, the minimum simulated NOx emissions (35.9 ppm@15%O 2 ) exceeds the regulatory limits, indicating that the RQL strategy alone cannot achieve compliance-grade emissions control when burning ammonia. • The migration of fuel-bound nitrogen in RQL combustion process was investigated. • Complete conversion of ammonia to nitrogen in the rich burning zone is the key to achieving low emissions. • The influence of flow on ammonia consumption was revealed. • The synergistic influence of multiple parameters on the emission performance was discussed and visually displayed.