Numerical analysis of internal flow characteristics of urea injectors for SCR dosing system

The urea SCR (selective catalytic reduction) system is an exhaust gas after-treatment system that reduces NOx from diesel engine exhaust gas. In this study, the internal flow characteristics of two types of commercial urea SCR injectors were analyzed, especially according to the injector needle lift. The two types of injectors considered in this study are the H type, which has three nozzles, and the D type, which has one nozzle. Various analysis methods were applied for evaluating and estimating the performance characteristics of the injectors. The reverse engineering method was applied for modeling commercial injectors, and a computational model was developed for simulating the mutual counteraction of the injector needle and the urea solution. The H-type injector shows relatively better urea solution supply characteristics and attains the steady flow condition faster than the D-type injector. Furthermore, the average discharge coefficient of the D-type injector is 0.53, whereas that of the H type is 0.59. The injector flow characteristics data obtained in this study could be used as basic design information for further development of urea SCR injectors.