Experimental Investigation of AdBlue Film Formation in a Generic SCR Test Bench and Numerical Analysis Using LES  
[PERSON]  
1 Institute for Reactive Flows and Diagnostics, Technical University of Darmstadt, 64287 Darmstadt, Germany; [PERSON]DDRESS] (A.S.); [PERSON]DRESS] (M.B. ); [PERSON]_ADDRESS] (A.S.); [EMAIL_ADDRESS] (A.D.)  
[PERSON]  
1 Institute for Reactive Flows and Diagnostics, Technical University of Darmstadt, 64287 Darmstadt, Germany; [PERSON]DDRESS] (A.S.); [EMAIL_ADDRESS] (A.S.); [EMAIL_ADDRESS] (A.D.)  
[PERSON]  
2 Institute for Fluid Mechanics and Aerodynamics, Technical University of Darmstadt, 64287 Darmstadt, Germany; [PERSON]ADDRESS] (I.V.R. ); [PERSON]ADDRESS] (J.H.) [PERSON]  
1 Institute for Reactive Flows and Diagnostics, Technical University of Darmstadt, 64287 Darmstadt, Germany; [PERSON]DDRESS] (A.S.); [PERSON]DRESS] (M.B. ); [PERSON]_ADDRESS] (A.S.); [PERSON]DDRESS] (A.D.)  
[PERSON]  
1 Institute for Reactive Flows and Diagnostics, Technical University of Darmstadt, 64287 Darmstadt, Germany; [PERSON]DDRESS] (A.S.); [PERSON]_ADDRESS] (A.S.); [PERSON]DDRESS] (A.D.)  
[PERSON]  
1 Institute for Reactive Flows and Diagnostics, Technical University of Darmstadt, 64287 Darmstadt, Germany; [PERSON]DDRESS] (A.S.); [PERSON]DRESS] (A.S.); [PERSON]DDRESS] (A.D.)  
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Although de-NOx SCR has been widely adopted, it still has significant shortcomings. In practice, AdBlue is atomized and injected into the process as a spray. Wetting of the walls of the exhaust system during the injection of the liquid urea solution is an especially undesirable and efficiency-reducing process that can compromise its robustness. The liquid film can flow into the catalytic converter and block it upon the formation of solid byproducts under given adequate temperature and residence time [4]. Furthermore, as the film formation influences the amount of ammonia supplied to the catalytic converter, it affects the effectiveness of the urea dosing strategy. The hydrodynamics of drop and spray impact are governed by inertia, surface tension and viscosity. The phenomena of drop impact onto a dry wall and the edge of the film flow generated by spray impact are also influenced by the substrate wettability and morphology. The outcomes of a single drop impact in the isothermal case include mainly rebound, deposition, prompt or corona splash. If the drop velocity is above the splashing threshold [5] the impact leads to the generation of a number of secondary drops. Several comprehensive reviews of the state-of-the art of the phenomena and modeling in the field of spray and drop impact can be found in the literature [6; 7; 8; 9]. In the case of spray or drop impact onto a hot substrate, the flow is influenced significantly by the microphysical thermodynamic processes caused by liquid evaporation and boiling [10; 11]. The heat flux at the substrate interface during spray impact also depends significantly on the thermodynamic or hydrodynamic regime of the interaction. An example of the boiling curve for the evolution of the heat flux over the target temperature, is shown in Figure 1a. If the wall temperature is higher than the Leidenfrost point, the impinging liquid drop rebounds from the substrate since a thin vapor layer between the wall and the spreading liquid prevents wall wetting, as shown in Figure 1b. At lower temperature, as illustrated in Figure 1c,d some wetted spots of boiling liquid appear on the hot substrate [12]. Their relative area increases in time as soon as the substrate is cooled by the spray.