A SCR Model Calibration Approach with Spatially Resolved Measurements and NH₃ Storage Distributions

The selective catalytic reduction (SCR) is a technology used for reducing NO_x emissions in the heavy-duty diesel (HDD) engine exhaust. In this study, the spatially resolved capillary inlet infrared spectroscopy (Spaci-IR) technique was used to study the gas concentration and NH₃ storage distributions in a SCR catalyst, and to provide data for developing a SCR model to analyze the axial gaseous concentration and axial distributions of NH₃ storage. A two-site SCR model is described for simulating the reaction mechanisms. The model equations and a calculation method was developed using the Spaci-IR measurements to determine the NH₃ storage capacity and the relationships between certain kinetic parameters of the model. A calibration approach was then applied for tuning the kinetic parameters using the spatial gaseous measurements and calculated NH₃ storage as a function of axial position instead of inlet and outlet gaseous concentrations of NO, NO₂, and NH₃. The equations and the approach for determining the NH₃ storage capacity of the catalyst and a method of dividing the NH₃ storage capacity between the two storage sites are presented. It was determined that the kinetic parameters of the adsorption and desorption reactions have to follow certain relationships for the model to simulate the experimental data. The modeling results served as a basis for developing full model calibrations to SCR lab reactor and engine data and state estimator development as described in the references (Song et al. 2013a, b; Surenahalli et al. 2013).