Development of a 2D Model of a SCR Catalyst on a DPF

A computationally efficient, 2D SCR catalyst on a DPF (SCR-F) model was developed to simulate the pressure drop, filtration efficiency, outlet NO, NO₂, and NH₃ concentrations, PM, temperature, and NH₃ storage distributions. The model extends previous work (Mahadevan et al. :J. Emiss. Control. Sci. Technol.1, 83–202, 2015; Mahadevan et al. :J. Emiss. Control. Sci. Technol.1, 255–283, 2015; Mahadevan et al.:J. Emiss. Control. Sci. Technol. 3, 171–201, 2017) by adding a 2D reaction-diffusion scheme-based chemical species solver with SCR reactions inside the substrate wall (Park et al. :Ind. Eng. Chem. Res. 51, 5582–15592, 2012). The experimental data (Kadam, 2016) used for the model calibration was collected on a Johnson Matthey SCRF® operated with a 2013 Cummins 6.7L ISB engine with tests spanning a wide range of operating conditions including PM loading and oxidation with and without urea injection. The major features in the model consist of (a) inhibition of SCR reactions by wall PM, (b) SCR reaction–based energy release, and (c) diffusion in the channels, forward diffusion between PM cake and substrate wall layers. The model can simulate transient conditions including the prediction of a 60–70% decrease in the NO₂-assisted PM oxidation rate during urea injection, 2D temperature distribution within 5 °C of the experimental data, and the resulting PM and NH₃ storage distribution by simulating the 10–15 °C temperature rise during urea injection. The maldistribution of NO, NO₂, and NH₃ concentrations caused by the temperature distribution and the inhibition of SCR reactions by PM in the substrate wall was simulated and the resulting outlet emissions agreed with the experimental data. The model can also be used for 2D CPF analysis by turning off the SCR reactions.