Optimal Design of Urea-SCR System for Reduction of NOx in Diesel Passenger Cars

Abstract

Much attention has been paid to reduce NOx in diesel engines so that many technologies for diminution of NOx have been developed for last few decades. Among them, the urea-SCR is well known to one of the most efficient method of reducing NOx emissions in the after-treatment devices of diesel passenger cars and light duty vehicles. In the present work, the computational prediction of internal flow and spray characteristics in the urea-SCR system was carried out by using computational field dynamics (CFD) simulation to evaluate NH₃ uniformity index (NH₃ UI) and its activation time. The number of nozzle and its diameter, injection directions and mounting positions are most important design factors and they are chosen as the design variables. The optimal solutions are obtained by coupling the CFD analysis with Taguchi method. The L₁₆ orthogonal array and small-the-better characteristics of the Taguchi method are used and the optimal values are confirmed to be valid in 95 % confidence and 5 % significance level through analysis of variance (ANOVA). The results show that the optimal values of the NH₃ UI and activation time (NH₃ UI 0.92) are obtained by 0.96 and 0.063 second, respectively and their values are improved by 4.4 and 37.2 %, respectively, compared with those of the base model.