Journal of Mechanical Science and Technology 30 (6) (2016) 2873~2880 www.springerlink.com/content/1738-494x(Print)/1976-3824(Online) DOI 10.1007/s12206-016-0546-2 Experimental verification of optimized NO X reduction strategies in a decrepit Euro-3 diesel engine retrofitted with a cooled EGR system † Hoon Lee, Taehun Ha and Hoimyung Choi * Vehicle Energy Research Laboratory, Intelligent Vehicle Platform Center, Advanced Institutes of Convergence Technology, Suwon, Gyeonggi-do 16229, Korea (Manuscript Received November 23, 2015; Revised January 22, 2016; Accepted February 10, 2016) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract 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. Accord- ingly, 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 metro- politan 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 cost- effectiveness. In this study, NOx characteristics of a decrepit Euro-3 diesel engine are thoroughly analyzed before and after the installa- tion of the EGR coolers with different cooling capacities. By applying real time control of EGR rate and exhaust backpressure in calibra- tion procedures, optimized NOx reduction strategies are established. Keywords: Diesel engine; NOx emission; PM emission; EGR cooler ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction Ultimately, improving air quality in metropolitan areas, mitigating climate change such as global warming, and devel- oping more energy-efficient transportation means all affect quality of life and pose major challenges to contemporary scientists and engineers. What the issues have in common is that they are all closely related to engine emissions from fossil fuel-powered transportation means, which is related to signifi- cant environmental concerns and human health deterioration. Thus, global standards regulating the toxic emissions have become increasingly stringent in all over the world over the last two decades. Accordingly, tremendous efforts have been put into transportation research and development to meet the standards, and eventually to improve quality of life. Chemical composition and concentration of each emission component varies depending on the combustion characteristics that originally caused the emission formation. Among those, NOx emissions such as Nitrogen monoxide (NO) and Nitrogen dioxide (NO 2 ), formed as a result of burning diesel fuel at very high temperature, are considered especially injurious. NOx not only causes acid rain, also destroys the balance of natural ozone (O 3 ) formation resulting in increasing of human diseases occurrences such as skin cancer. Accordingly, in European countries where the diesel vehicles are predominant in the car market, a series of strict emission standards called Euro-x, defining the permissible level of NOx emissions of new cars sold in the whole European Union (EU), have been used since 1993. Diesel penetration in Europe has gradually increased since the late 1990s and has reached above 50% in both new cars registered and market share in 15 member states of EU (EU15) and three European Free Trade Association (EFTA) countries [1]. For the permissible level of NOx emissions de- fined in the standards, overall, the dramatic strengthening of the regulations occurred between Euro-3 and Euro-4 [2]. New cars sold now emit significantly less NOx with ad- vanced engine combustion and exhaust aftertreatment tech- nologies that have been developed so far to meet the latest emission standards. However, in Europe, NOx emissions re- main one of the few emissions that have decreased less than other pollutants. This is mainly due to the continuous growth * Corresponding author. Tel.: +82 31 8889047, Fax.: +82 31 8889162 E-mail address: hoimyung@snu.ac.kr † Recommended by Associate Editor Jeong Park © KSME & Springer 2016