To meet the demand of the stricter emission limitations of NOx emissions in the new emission standards, selective catalytic reduction system has become an essential part in diesel engines. Currently, mitigation of urea crystallization and improvement of the mixing quality of ammonia are two crucial issues in diesel engines equipped with SCR system. In this paper, the flow dynamics, heat transfer, spray atomization and evaporation as well as the formation of urea deposits were predicted by a validated CFD model using fluid-solid coupling method. On the basis of this model, different mixer designs and spray cone angles were assessed. According to the results, the change of film mass is consistent with that of solid urea. In this case, solid urea could be used as an indicator for urea crystallization prediction. In view of different mixer designs, mixer with a cylindrical region in the center and two curved baffles around the cylindrical region could mitigate the formation of urea crystallization and achieve high mixing quality. When this kind of mixer is adopted, using smaller spray cone angles could further reduce the tendency of urea crystallization, raise the evaporation rate and improve the mixing uniformity.

为满足新排放标准对氮氧化物排放的更严格的排放限制要求，选择性催化还原系统已成为柴油发动机必不可少的组成部分。目前，减少尿素结晶和提高氨的混合质量是配备 SCR 系统的柴油发动机的两个关键问题。在本文中，流动动力学、传热、喷雾雾化和蒸发以及尿素沉积物的形成通过使用流固耦合方法的经过验证的 CFD 模型进行了预测。在此模型的基础上，评估了不同的混合器设计和喷雾锥角。结果表明，薄膜质量的变化与固体尿素的变化一致。在这种情况下，固体尿素可以作为尿素结晶预测的指标。针对不同的搅拌机设计，中心有圆柱形区域和圆柱形区域周围有两个弯曲挡板的混合器可以减少尿素结晶的形成并实现高混合质量。采用这种混合器时，使用较小的喷射锥角可以进一步降低尿素结晶的倾向，提高蒸发速度，提高混合均匀度。