Investigation on the reduction in unburned ammonia and nitrogen oxide emissions from ammonia direct injection SI engine by using SCR after-treatment system

Currently generated nitrogen oxides (NO_x) and unburned ammonia (NH₃) can be converted into nitrogen and moisture that are harmless to the human body and environment using selective catalytic reduction (SCR). The concentrations of NO_x and unburned NH₃ emitted from the ammonia combustion engines are significantly higher than those emitted by engines using existing hydrocarbon fuels. In this study, ammonia, a representative carbon-free fuel, was used in spark ignition engines for existing passenger vehicles to identify the trends in exhaust gases emitted from engines and conduct experiments on after-treatment strategies to reduce NO_x and unburned NH₃. The addition of oxygen significantly maximized the conversion efficiency of the SCR after-treatment system by changing the concentration of both NO_x and NH₃ in the exhaust gas.