Simulating UWS Droplet Phase Change and Heat Transfer

Mario F.  Trujillo, UW-Madison

Spray modeling efforts for UWS SCR technologies have almost entirely treated the thermal process involving UWS spray droplets as undergoing water vaporization followed by direct gasification of the Urea particle into NH3. This approach also applies to wall deposits formed from spray impingement. While this process accurately captures the production of NH3 occurring at lower temperatures, it does not consider the creation of Biuret, ammeline, cyanurates, ammelide, as well as other chemical constituents, which take place at higher temperatures. It is precisely these chemicals that are of concern due to their toxicity. As documented in the literature their production is highly temperature dependent, which implies that an adequate thermal numerical treatment is required for their predictions. In our present modeling effort, we focus first on the phase change characteristics of an initial UWS droplet exposed to a hot environment. The physical processes are fully resolved spatially and temporally using an Arbitrary-Lagrangian-Eulerian meshing strategy. Similarly, the heat transfer dynamics occurring in a liquid film with multiple droplet impingements are captured employing a Volume-of-Fluid methodology. This effort will form the framework for subsequent chemical analysis of the previously mentioned species formation, and will provide spray models to be used at a more global scale for modeling UWS dosing processes.

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