Selective catalytic reduction is the most promising technique for NOx reduction from diesel engine exhaust emissions. The greatest challenge to implementing the system is solid deposit formation. Spray wall impingement of UWS was investigated in a constant volume chamber by numerical simulation using STAR CCM+ CFD code. The realizable k-epsilon two-layer approach together with standard wall functions and all y+ treatment was implemented for the modeling of turbulence flow. The two-phase flow was modeled by using Eulerian- Lagrangian approach. The heated wall temperature was maintained from 338 K to 573 K during the UWS spray wall impingement. The development of the spray after impinging on the heated wall was visualized and measured. UWS droplet size distribution, wall film formation and droplet evaporation rates were estimated, which are vital parameters for the system performance but not well researched. User-defined functions (UDF) were developed to input the Leidenfrost temperature limit in the calculation and to estimate the desired parameters. The investigation reveals that wall temperature is the most important parameter that significantly affects spray development after impingement, droplet size distribution, wall film formation and droplet evaporation. Increasing the wall temperature leads to longer spray front projection length, smaller droplet size, faster droplet evaporation and smaller film thickness, which are preconditions for urea crystallization reduction. The numerical model and parameters were validated by comparing with experimental data.
