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An external injection system was introduced to control the lean Nox trap(LNT). LNT absorbs Nox in lean condition of exhaust gas and discharges N2 by reducing Nox in rich condition. To make exhaust gas lean or rich, fuel injection into the exhaust gas is used with the engine control. There are two ways to add a reducing agent into exhaust gas. One is post injection using common rail system and the other is external injection. The external injection has prior benefit; can be controlled independently without disturbing engine control, can be adapted to various layout of exhaust system, has no oil dilution problem, and etc. In this study the effect of an external fuel injection on the control of LNT system was investigated. At first, the injection characteristic of the external injection was analyzed: flow rate and atomization characteristic was controlled by the PWM signal and the fuel pressure. Then the external injection system was introduced into NPRS(Nox PM Reduction System).

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.

A NOx absorber and a fuel cracking catalyst were combined to investigate whether this could increase the low temperature activity of a NOx absorber system. Before engine exhausted gas tests, the activity and properties of the NOx absorbing catalyst were examined by simulated gas and temperature programmed desorption. Diesel fuel cracking catalysts were designed to maximize the hydrogen productivity. From the hexadecane reaction experiments for these catalysts, it was found that the hydrogen generation amount was significant even at 200°C. Engine bench test results with the diesel fuel cracking catalysts confirmed the improvement of NOx removal efficiency. In case of high NOx capacity with prolonged regeneration interval condition showed the best results. It reflects the importance of optimization of the NOx absorber and the pre-oxidation catalyst, the regeneration strategy.