Real-time dynamics of amperometric exhaust oxygen sensors

Previously, we had identified the various dynamic mechanisms of a wide range air to fuel ratio sensor operated in the engine exhaust by using the transfer function approach. In this study, we utilized these results to model the real time sensor response to an engine exhaust excursion. Generally, the model fits the real time sensor data well. In the fitting, we identified a new dynamic mechanism, which was not detected in the previous transfer function study. This new dynamic occurred at the stoichiometric point when the engine changed from rich to lean. This new mechanism involved the depletion of the adsorbed fuel species on the electrode surface by an oxidation process. The dynamics of this effect depends on the ratio of the diffusion flux of the sensor-coating layer to the total adsorbed gas species on the electrode surface. The smaller the ratio is, the slower the dynamic mechanism becomes.