Experimental verification of optimized NOX reduction strategies in a decrepit Euro-3 diesel engine retrofitted with a cooled EGR system

Vehicle-produced NOx is among emissions that deteriorate human health and the environment. To regulate the NOx emissions from transport, especially from diesel-powered vehicles, various standards have been established globally, and regulations are becoming more stringent across the world. Considerable NOx from diesel vehicles are due to the compression ignition characteristics of engines. Accordingly, to meet the national and global standards, manifold advanced aftertreatment technologies, such as EGR, SCR and LNT, have been developed and widely adopted since introduction of the Euro-4 standards in 2006. In Korea, current allowable NOx standards have been greatly reinforced to one fourth of the permissible level in 2004 and one sixth in 2000. However, the percentage of diesel vehicles in Korea more than 10 years old, manufactured prior to Euro-4, is still significant, accounting for 29% of passenger vehicles, 32% of buses, and 45% of trucks in total registration. Against this backdrop, tremendous efforts are required to improve air quality, especially in metropolitan areas. Of all technical options currently available, installing a cooler to typical EGR systems is considered as a more efficient way for superannuated diesel vehicles to meet the Euro-4 than installing a SCR or LNT in terms of technical acceptability and costeffectiveness. In this study, NOx characteristics of a decrepit Euro-3 diesel engine are thoroughly analyzed before and after the installation of the EGR coolers with different cooling capacities. By applying real time control of EGR rate and exhaust backpressure in calibration procedures, optimized NOx reduction strategies are established.