Investigation of flow and acoustic behavior of urea mixers used in SCR systems

Today, with the increasing global population and the subsequent rise in the number of vehicles, strict controls and limitations are being imposed to minimize the negative effects of exhaust gases on the environment and human health. To reduce NOx emissions in diesel-powered vehicles, ADblue additive (ammonia) and SCR systems have been introduced. A urea mixer is used to achieve better mixing of the ADblue additive in SCR systems and to obtain effective results. In SCR systems, it is essential for the urea mixer to generate low backpressure, as high backpressure negatively affects performance, and for the NH3 homogeneity index (UI NH3) to be high for the SCR system to function effectively. Urea mixers exhibit different performances based on parameters such as the number of blades, blade angle, and blade length. In this study, the impact of mixers on backpressure and UI NH3 was analyzed using a numerical analysis method, considering 27 different mixers and their parametric effects. The results were examined by varying blade lengths, blade angles, and the number of blades. The target was to have backpressure lower than 1 kPa and a UI NH3 value higher than 0.85. Among them, six mixers that met these criteria were prototyped, and experimental backpressure tests and UI NH3 measurements were conducted to validate the results. Sound transmission loss measurements were carried out to assess their acoustic performance and behavior. The study revealed that the number and length of blades increased backpressure but had no effect on the UI NH3 value.