Comparing Breakup Models in a Novel High Injection Pressure SCR System using Polyhedral Meshing

A novel high pressure SCR spray system is investigated both experimentally and numerically. RANS simulations are performed using Star-CD and polyhedral meshing. This is one of the first studies to compare droplet breakup models and AdBlue injection with high injection pressure (P_inj=200 bar). The breakup models compared are the Reitz-Diwakar (RD), the Kelvin-Helmholtz and Rayleigh-Taylor (KHRT), and the Enhanced Taylor Analogy Breakup (ETAB) model. The models are compared with standard model parameters typically used in diesel fuel injection studies to assess their performance without any significant parameter tuning. Experimental evidence from similar systems seems to be scarce on high pressure AdBlue (or water) sprays using plain hole nozzles. Due to this, it is difficult to estimate a realistic droplet size distribution accurately. Thereby, there is potential for new experimental data to be made with high pressure AdBlue or water sprays. Engine experiments carried out in the present study give indication on the correct magnitude of the droplet sizes appearing in the experimental system because high NO_x conversion rates were measured without any urea crystallization into the system. It seems plausible that relatively small droplet sizes are needed for complete evaporation of all droplets within suitable time and space. Therefore, the results predicted by the KHRT model appear most reliable.