Exhaust after-treatment devices for NO_x reduction have become mandatory for achieving the strict diesel emission standards. The selective catalytic reduction (SCR) method has proven to be efficient in this task. Nonetheless, in order to improve the efficiency of the system, the urea–water solution (UWS) injection process needs to be properly characterized due to the limited geometry of the exhaust line and its flow conditions. In combination with the experimental analysis into the system in a dedicated test rig, computational fluid dynamics studies provide better insights into the physical phenomena. Therefore, the main objective of this investigation is to achieve validated droplet size and velocity distributions in the simulation when compared to experiments. Three different positions along the spray are evaluated for that. The methodology adopted includes an Eulerian–Lagrangian approach to study the UWS spray. The results obtained with it show a proper experimental validation as well as the Sauter mean diameter distribution for the conditions tested. The proposed model accurately reproduces the main spray characteristics for different injection pressures and ambient conditions. Thus, the main conclusions obtained sum up in a good methodology for predicting UWS sprays in SCR-like conditions.

中文翻译：

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尿素-水溶液喷雾的计算研究，用于分析类似SCR的注入过程

排气后处理装置对NO _X为了达到严格的柴油排放标准，减少排放已成为强制性要求。选择性催化还原（SCR）方法已被证明在该任务中是有效的。但是，为了提高系统效率，由于排气管路的几何形状及其流动条件的限制，必须适当表征尿素水溶液（UWS）的喷射过程。结合在专用测试台中对系统进行的实验分析，计算流体动力学研究可以更好地了解物理现象。因此，与实验相比，本研究的主要目的是在模拟中获得经过验证的液滴尺寸和速度分布。为此评估了沿着喷雾的三个不同位置。所采用的方法包括研究UWS喷雾的欧拉-拉格朗日方法。用它获得的结果显示了适当的实验验证以及在所测试条件下的索特平均直径分布。所提出的模型可以精确再现不同喷射压力和环境条件下的主要喷雾特性。因此，获得的主要结论是在预测类似SCR的条件下进行UWS喷雾的良好方法中总结的。