CFD study of SDPF flow characteristics according to variations in urea injection strategy and device design

Commercial diesel engines apply reduction devices such as Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), and Selective Catalyst Reduction (SCR) for NO_x reduction in order to respond to strengthening exhaust regulations such as EU7. Recently, SCR-Catalyzed Diesel Particulate Filters (SDPF) is used to maximize the SCR reaction area and achieve compact design. In order to maximize NO_x reduction efficiency, SDPF should be designed so that the urea-water sprayed from the front of the porous substrate is distributed and the ammonia slip is minimized. However, flow uniformity and back pressure are generally in a trade-off relationship, and in some existing vehicle SDPFs, a problem was raised where some urea flows through the bottom of the pipe. To overcome these limitations, this study applied L-shape elbow pipe to the front end of SDPF and performed flow analysis according to changes in the urea injection strategy and design of the urea mixer. As a result of the study, it was found that the SDPF flow uniformity could be improved by 13.9 %, 1 %, and 4 % respectively through optimal modification of mixer installation and angle, injector angle, and injector location, while minimizing the increase in back pressure. Based on these findings, an L-shape elbow pipe SDPF design strategy was derived, and the correlation between exhaust flow uniformity and back pressure was identified. To address these performance challenges, this study was conducted to establish a CFD-based optimization framework that evaluates and enhances NH₃ distribution uniformity and minimizes back pressure by modifying mixer geometry and urea injection strategy.