Modeling the Gasification Process of Urea-Water-Solution Droplet
Mario Trujillo, University of Wisconsin
In an effort to optimize the after-treatment process, the three-dimensional modeling of Urea-Water-Solution (UWS) sprays is now being readily used as evidenced by the relatively large number of research articles on the subject. In spite of these advances, the treatment given to the gasification process of each UWS droplet often suffers from simplifications that are inconsistent with the physics. Some of these include a complete evaporation of water prior to the gasification of Urea and a rapid-mixing model treatment. In the present work, an effort is made to address these shortcomings by directly resolving the temperature and species field of a UWS droplet coupled to the jump conditions and phase equilibria constraints. The numerical code is validated by systematically testing various aspects of the physical system. It is shown that the uncertainty in droplet vaporization experimental data is not negligible, particularly for the UWS case. Reasons for this uncertainty are given and their implications for the development of numerical models is discussed. Moreover, the delicate state of the UWS is studied thermodynamically eluding to the fact that under certain conditions more than two phases can coexist. This complicates the physics well beyond the general treatment given in the literature.