Browse Publications Technical Papers 2022-28-0325
2022-10-05

Design Optimizations of Static Dual-Stage Mixer for SCR Layout to Improve UWS Conversion Efficiency 2022-28-0325

Aftertreatment system meeting BS-VI emission regulations for diesel engines led to a decrease in NOx emissions to a low level. Selective catalyst reduction (SCR) is the most prominent and mature technology used to reduce NOx emissions. Initially, the UWS injection layout was designed without any mixer which resulted in low NH3 uniformity on SCR monolith with reduced UWS conversion efficiency, leading to concentrated wall spray loads. A dual-stage static mixer was designed and introduced to enhance the proper mixing of UWS droplets with exhaust gas upstream, to accelerate UWS breakup and evaporation of droplets. The mixer blades enhance the local turbulence, which resulted in a high mixing degree of droplets with the exhaust gas stream, thus reducing the crystallization risk at the mixer and the surrounding area. Mixers also extend the evaporation path, residence time, and thermal decomposition for droplets. Mixer shape was optimized with various design parameters with good structural and thermal flow integrity like: (blade orientations, width, length, angles, mixer layout position, and thickness) for effective thermolysis and hydrolysis reaction, which results in better ammonia uniformity, with minimized wall film urea deposits and its by-products. Design optimizations were carried out using commercial CAD and CAE tools. The results show that the optimized mixer can improve, (a). Atomization performance of UWS spray, (b). Evaporation and decomposition efficiency of urea water droplets, (c). The distribution uniformity of NH3 gas and obtained numerical results were compared with experimental data.

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