Study on the Performance Characteristics of Urea-SCR System in the ETC Test

Abstract: To meet the NOx limit without a penalty of fuel consumption, urea-SCR system is currently regarded as promising NOx reduction technology for diesel engines. SCR system has to achieve maximal NOx conversion in combination with minimal NH3 slip. In this study, the performance characteristics of urea-SCR system with open loop control were assessed in the European Transient Cycle(ETC) for heavy duty diesel engine. The SCR inlet temperaure varied in the range of 200 to 340°C in the ETC cycle. Open loop control calculated the urea flow rate based on the NOx and NSR map which gave for each combination of SCR inlet temperature and space velocity the normalized NH3 to NOx stoichiometric ratio which resulted in a steady-state NH3 slip of 20ppm. During the ETC cycle, the open loop control with the optimized NSR offset achieved NOx reduction of 80 % while keeping the average NH3 slip below 10ppm and maximum 20ppm. It was also found that NOx sensor was cross-sensitive to NH3 and a control strategy fo