Review on the interaction mechanism of nitrogen/sulfur pollutants during fuel combustion

Abstract The formation and control of pollutants emitted from fuel combustion have always been a focal point in combustion chemistry. Key pollutants primarily include nitrogen oxides (NOx) and sulfur oxides (SOx), making it crucial to elucidate the formation processes of nitrogen and sulfur components during combustion for pollutant control. Due to the highly coupled evolution processes of both components, independent reaction mechanisms struggle to describe this process, thus considering the interactions between them is significant for the evolution of nitrogen and sulfur components. This paper investigates the promotional or inhibitory effects between nitrogen and sulfur components in fuel combustion experiments, with the magnitude of this interactive effect varying between 2% and 250%, contingent upon the equivalence ratio and the N/S ratio impacts. Additionally, from a microkinetic perspective, two mechanisms underlying N/S interactions are identified: direct and indirect interactions. Direct interaction involves the formation of NS radicals, primarily through direct reactions of nitrogen species (NOx/HCN/NHi, where i ranges from 0 to 3) with sulfur constituents (SOx/H2S). Conversely, indirect interaction alters the radical pool via the intervention of NO or SO2, subsequently influencing each other's reaction pathways. It is noted that the current reaction system is incomplete, lacking key reactions, while the kinetic parameters of some reactions are still contentious. Advanced theoretical calculations are needed to refine the N/S interaction reaction model, in order to provide more accurate predictions for nitrogen and sulfur pollutant levels.