Droplet–Wall Interaction Dynamics during Urea Dosing in an Aftertreatment System

Urea–water solution (UWS) is sprayed during selective catalytic reduction (SCR) in the aftertreatment system of a diesel engine. UWS decomposes to ammonia and reacts with harmful nitrogen oxides present in exhaust gas to convert it to harmless nitrogen and water vapor. The interaction of UWS spray droplets with the hot wall of the aftertreatment system plays a crucial role in the performance and life of the aftertreatment system used in modern diesel engines for emission control. We report here a comprehensive experimental investigation on the normal impact of UWS droplets on the heated wall of stainless steel (SS410), mimicking the droplet–wall interaction in an SCR aftertreatment system. We have built a regime map underlying the possible outcomes under operating conditions encountered in an SCR system. The transition zones are identified, and the complex transition dynamics from one regime to another are discussed. Finally, we investigate and discuss the universality of the non-dimensional parameters used to characterize drop impingement on a heated wall. Present study will help to develop strategies to avoid the urea deposits on the walls of an SCR system.