This paper describes how to meet LEVII ULEV70 emission standards and minimize fuel consumption with the combined NOx after-treatment (LNT+SCR) system for diesel vehicles.
Through analysis of LNT's functionality and characteristics in a LNT+SCR combined after-treatment system, allowed a new control strategy to be established, different from the existing LNT-only system. In the 200°C or higher condition where SCR can provide the most stable NOx conversion efficiency, rich regeneration of LNT was optimized to minimize LNT deterioration and fuel consumption. Optimized mapping between rapid heat up strategy and raw NOx reduction maximized LNT's NOx conversion efficiency during the intervals when it is not possible for SCR to purify NOx This study used bench aged catalysts which were equivalent to 150K full useful life.
During the Highway (HFET) driving cycle when the SCR conversion rate is generally high, fuel economy was improved by minimization DeNOx in LNT and improvement of the engine combustion efficiency.
In conclusion, this study provided a solution to optimize a combined after-treatment system, leading to test results that met EPA 150K Emissions regulations. This study also found that an LNT+SCR after-treatment system which can meet sea level EPA FTP-75 emissions regulations is able to also meet high-altitude and highway emissions regulations.