Modeling and analysis of pumping cell of NOx sensor – Part Ⅰ: Main oxygen pumping cell

To improve the performance of the NOx sensor, a combined model based on the electrochemical model and the diffusion model is developed for the main oxygen pumping cell of the NOx sensor. One important feature of this combined model is that the model eliminates the intermediate variable and only shows the relationship between the pumping voltage and the pumping current. To validate the model at different gas concentrations, the sensor is mounted on the designed test rig. Then, the simulation results are compared with experimental data from the test rig and good agreement is obtained. Comparing the cathode and anode overpotential, it is found that the anode concentration overpotential can be ignored. In addition, since the activation overpotentials of the cathode and anode are relatively small, they can all be regarded as linear changes with the pumping current. The subsequent characteristic analysis determines the changes of the internal characteristics of the sensor during operation, which will provide guidance for the design and control of the sensor.