Efficient Modeling of SCR Urea Deposits Formation Using ANSYS Fluent

Selective Catalytic Reduction (SCR) systems, used for exhaust gas aftertreatment in diesel engines and newly designed H2 engines, are pushed for efficiency by strict emission regulations and requirements for fuel efficiency in road vehicles, ships and power stations. To reduce costs and time during the development process of such systems, CFD is an adequate tool to investigate and improve geometrical designs. Such CFD models require coupled physics like turbulent gas flow, liquid sprays that impinge on hot walls considering complex splashing regimes and formed wall-films driven by gas shear and gravity. All these sub-flow systems exchange momentum, energy and mass via vaporization and chemical reactions. SCR aftertreatment is prone to solid deposit formation on the walls, which hinders heat transfer and causes increased pressure losses. Therefore, it is crucial to be able to predict deposition locations and rates and optimize vaporization of water-urea droplets and mixing of gaseous urea into the exhaust gas stream. This paper presents recent improvements of the Euler/Lagrange wall film model in Fluent which allow efficient simulation of urea deposits over more than fifty cycles in less than a few days by using a chemistry model from literature (Brack et al., 2016) to compute homogeneous chemical reactions in the film and heterogeneous reactions between gas and film. The CFD model is validated using results from thermogravimetric measurements and experimental SCR test rigs from available literature.