Computational Study of Urea-Water Solution Sprays for the Analysis of the Injection Process in SCR-like Conditions

Exhaust after-treatment devices for NOx 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.