Physics-Based Characterization of NSCR Operation Part 1
This paper presents the work done to date on a modeling study of the Non-Selective Catalytic Reduction (NSCR) system. Several recent experimental studies indicate that the voltage signal from the heated exhaust gas oxygen sensor commonly used tocontrol these emission reduction systems may not be interpreted correctly because of the physical nature in the way the sensor senses the exhaust gas concentration. While the current signal interpretation may be satisfactory for modest NOx and CO reduction, an improved understanding of the signal is necessary to achieve consistently low NOx and CO emission levels. This model simulates the output from a planar switch type lambda sensor. The model consists of three modules. The first module models the multi-component mass transport through the sensor protective layer. A one-dimensional mass conservation equation is used for each exhaust gas species. Diffusion fluxes are calculated using Maxwell-Stefan equation. The second module includes all the surface catalytic reactions taking place on the sensor platinum electrodes. All kinetic reactions are modeled based on Langmuir- Hinshelwood kinetic mechanism. The third module is responsible for simulating the reactions occurred on the electrolyte material and determining the sensor output voltage. The details of these three modules as well as a parametric study that investigates sensitivity of the output voltage signal to various exhaust gas parameters is provided in the paper.