Chemical effect of water addition on the ammonia combustion reaction

Ammonia has become an emerging fuel. However, its combustion product NOx is polluting, and it is necessary to explore its conversion process. To determine the effect of water addition on ammonia oxidation and NOx, reaction molecular dynamics simulations are performed to study the chemical reactions of ammonia. Ammonia oxidation is studied in O2/N2 and O2/H2O environments in a determining density and O2/NH3 ratio equal under high temperature conditions. This work focuses on the initial reaction path of ammonia combustion established through chemical trajectory analysis. The ammonia oxidation behavior, the distribution of the main products, and the corresponding time evolution behavior on the atomic scale are also studied. Finally, the interconversion processes of molecules containing N elements in the ammonia oxidation products are analyzed. Results show that when N2 molecules are replaced by H2O molecules, the formation of HNO increases with the net flux of the reactions: NH + OH -> H2NO, H2NO -> H + HNO. We also investigate the effect of different O2 concentrations. An increase of NO and HNO molecules with O2 concentration mainly from the reactions: O2 + H -> O + OH, H3NO + OH -> H2NO + H2O, H2NO -> H +HNO and HNO + OH -> H2O + NO. In addition, the conversion affected by water addition between NO and HNO occurs mainly in the middle time of the oxidation, and H2O enhances the severity of the oxidation with the number of OH radicals. Water addition provides a new way to control NOx emissions in ammonia combustion, that is, converting it into other H-containing compounds.

Automated summary

This study investigates the chemical reactions involved in ammonia oxidation and NOx formation through reaction molecular dynamics simulations. The effects of different environment conditions and water addition on ammonia oxidation behavior and product distribution are analyzed. The results show that water addition can effectively control NOx emissions in ammonia combustion.