Influence and correlation analysis of urea injection method and mixer combination on SCR performance

Abstract

As emission standards have been tightened globally, reducing nitrogen oxide (NO_x) emissions is a strict challenge for the internal combustion engine industry. In this paper, it aims to explore the effects of different urea injection methods and mixer combinations on the performance of the selective catalytic reduction (SCR) system, as well as to perform correlation analysis by using the computational fluid dynamics (CFD) method. Firstly, the total SCR system model including a urea injection device and mixer has been built after the numerical simulation method was validated by comparing the results of the experimental data. Secondly, the effects of different injection methods and mixer configurations on turbulence energy, ammonia (NH₃) distribution uniformity, pressure drop, and NO_x reduction (de-NO_x) efficiency were analyzed. It is revealed that the mixer combination can significantly improve turbulence energy and NH₃ uniformity. The center injection method can provide better NH₃ uniformity and lower pressure drop compared to the wall injection method. Among the double mixers, the T-E type mixer is demonstrated to have superior de-NO_x efficiency, while the E-type mixer excels in turbulence generation and mixing. Finally, the Analytic Hierarchy Process (AHP) has been used to assign weights to performance indicators, and the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) identified Case D1 as the optimal configuration. For the T-E type mixer, de-NO_x efficiency can be improved by over 10 %. For the center injection method, the pressure drop is reduced by 15 % and NH₃ uniformity is enhanced by 20 %. It is highlighted that the urea injection method and mixer combination play a critical role in optimizing SCR system performance and efficiency. At the same time, it also provides a systematic approach to solving problems by comprehensively considering the coordinated coupling actions between various components of the entire SCR system.