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Future emission limits of diesel engines require additional effort to develop advanced after-treatment devices. The Urea-SCR system is a promising device to reduce NOx emissions. The purpose of this work is to reduce NOx emissions from a Light Duty Vehicle (LDV) with a Urea-SCR (Selective Catalytic Reduction) system, a Catalytic Particulate Filter (CPF), and a Diesel Oxidation Catalyst (DOC). The purpose of the development is to analyze the atomization characteristics of the urea solution and to optimize the flow path shape in front of the SCR catalyst for uniform reductant (NH3) distribution. Additionally, the development purpose is to determine the strategy for urea solution injection quantity and to verify the performance of the Urea-SCR system on the vehicle. The NO2/NOx ratio plays a pivotal role in reducing NOx with Urea-SCR system. Although NO is converted into NO2 through the DOC, the NO2/NOx ratio is reduced due to the CRT (continuous regenerating trap) effect in the CPF.

Emission of carbon dioxide from mobile sources seriously concerned to solve greenhouse effect and high price of gasoline in some countries have resulted in the development of lean-burn concept engine. In spite of many studies on the lean deNOx catalyst, we have no clear solution to obtain high fuel economy and high efficiency of NOx conversion in lean-burn application. This paper describes applicability and problems of NOx adsorber system to partial lean-burn vehicle, the development of three-way catalyst with improvement of washcoat technology based on three-way catalyst used for gasoline application, and comparison test results of evaluations is synthesized gas activity test, Federal Test Procedure (FTP) test, etc. This study shows improved three-way catalysts in partial lean- burn vehicle have max. 89% of NOx conversion in FTP without adding rich spike and regeneration functions to engine management system.