Among the many options under investigation for deNOx solutions in the automotive industry, the use of selective catalytic reduction (SCR) is one of the most reliable, efficient, and cost-effective aftertreatment systems found thus far. The operational efficiency of SCR systems is strongly linked to the spray dynamics and uniformity of urea in the exhaust flow. Development and testing of different spray configurations require the investigation of different scenarios under exhaust like conditions. Most of the studies found in the literature assume water to be a sufficient alternative to urea-water-solution (UWS), principally based on a nondimensional analysis indicating that the spray dynamics should be similar. Substituting UWS with water offers advantages regarding test setup, safety, etc., but the assumption of sufficient similarity needs further investigation, especially when moving out of normal conditions, where evaporation rates and the subsequent species production might vary. In this study, a wind tunnel capable of reaching temperatures of up to 400° C at 10 m/s of cross-flow velocity was used to run a detailed comparison between water and UWS spray under different scenarios. Velocity and droplet-size distributions were obtained to characterize the sprays with a two-dimensional phase doppler anemometry instrument. Statistical quantities were constructed at key positions along the spatial development of the spray, which served to build a comparison matrix between the cases. Even though no significant differences were observed between the mean values, their distribution shapes did vary significantly, pointing toward different liquid evaporation rates in the heated cross-flow cases. Although a more detailed measurement campaign might be needed to confirm this final hypothesis, it is suggested that the evaporation rate of pure water diminishes the population of smaller droplets faster than in the UWS cases. Finally, this study provides some key findings to further investigate the physical cause for these differences, pointing toward where to draw a line on the replaceability of UWS by water during experimentation for SCR systems.

中文翻译：

---

商用 SCR 喷射器在静止和加热错流条件下的水和尿素水溶液喷射差异的实验研究

在汽车行业正在研究的众多脱硝解决方案中，选择性催化还原 (SCR) 的使用是迄今为止发现的最可靠、最有效和最具成本效益的后处理系统之一。SCR 系统的运行效率与废气流中尿素的喷雾动力学和均匀性密切相关。不同喷雾配置的开发和测试需要研究类似排气条件下的不同场景。文献中发现的大多数研究假设水是尿素水溶液 (UWS) 的充分替代品，主要基于表明喷雾动力学应该相似的无量纲分析。用水代替 UWS 在测试设置、安全性等方面具有优势，但足够相似的假设需要进一步研究，特别是在脱离正常条件时，蒸发速率和随后的物种产量可能会有所不同。在这项研究中，使用能够以 10 m/s 的横流速度达到高达 400°C 温度的风洞，对不同情景下的水和 UWS 喷雾进行了详细比较。使用二维相位多普勒测速仪获得速度和液滴尺寸分布以表征喷雾。在喷雾空间发展的关键位置构建统计量，用于构建案例之间的比较矩阵。尽管平均值之间没有观察到显着差异，但它们的分布形状确实存在显着差异，指向加热错流情况下不同的液体蒸发速率。尽管可能需要更详细的测量活动来证实这一最终假设，但建议纯水的蒸发速率比 UWS 案例更快地减少小水滴的数量。最后，本研究提供了一些关键发现，以进一步研究这些差异的物理原因，指出在 SCR 系统实验期间，在哪里划定 UWS 可被水替代的界限。