Review of Improving the NOx Conversion Efficiency in Various Diesel Engines fitted with SCR System Technology

The diesel engine is utilized in most commercial vehicles to carry items from various firms; nevertheless, diesel engines emit massive amounts of nitrogen oxides (NOx) which are harmful to human health. A typical approach for reducing NOx emissions from diesel engines is the selective catalytic reduction (SCR) system; however, several reasons make reducing NOx emissions a challenge: urea particles frequently become solid in the injector and difficult to disseminate across the system; the injector frequently struggles to spray the smaller particles of urea; the larger urea particles from the injector readily cling to the system; it is also difficult to evaporate urea droplets because of the exhaust and wall temperatures (Tw), resulting in an increase in solid deposits in the system, uncontrolled ammonia water solution injection, and NOx emissions problems. The light-duty diesel engine (LDD), medium-duty diesel engine (MDD), heavy-duty diesel engine (HDD), and marine diesel engine use different treatments to optimize NOx conversion efficiency in the SCR system. This review analyzes several studies in the literature which aim to increase NOx conversion in different diesel engine types. The approach and methods demonstrated in this study provide a suitable starting point for future research into reducing NOx emissions from diesel engines, particularly for engines with comparable specifications.