Process-Oriented Modeling of Urea-Water Solution as a Multi-Component Fluid with the Aid of Apparent Properties for CFD Spray Applications

In the control of exhaust gas pollution by selective catalytic reduction (SCR), computational fluid dynamics (CFD) gained a major role for design purposes. A crucial primary step is the characterization of the spray behavior of the reductant. Secondary, and not less important, is to capture the complete evaporation process of the urea-water solution (UWS). This work presents a new approach that utilizes the apparent properties of pure substances within the process-oriented framework of a two-liquid mixture. All properties are directly compared to accessible experimental and correlation-based data. Within the framework, a thermodynamically consistent vapor pressure for urea is derived that agrees with observations in the literature. Furthermore, an application-specific approach for urea decomposition kinetics is presented. Evaporation rates and spray applications are simulated and compared to own as well as experimental and simulation data from different authors. The limitations of the model are identified, presented, and discussed.