A Variable-Potential Amperometric Hydrocarbon Sensor

Using the understanding of an inexpensive production NOx sensor, the operating parameters are changed to enable hydrocarbon measurement using the same sensor. A limiting-current-type amperometric hydrocarbon sensor for rich conditions (in the absence of O-2) is developed in this work. To do this, an inexpensive three-chamber amperometric sensor with three separate electrochemical cells is parameterized to measure propane concentration. The sensor is tested using a controlled sensor test rig at different propane concentrations. The inputs to the sensor electrochemical cells have been modified to determine the best HC measurement parameters (HCMPs) for measuring propane at different concentrations. First, the transient performance and stability of the sensor are optimized by changing the sensor temperature, the reference cell potential, and the stabilizing cell potential at a high propane concentration (5000 ppm - balanced with nitrogen). Over the range tested, the sensor has the longest stable output duration at the temperature of 1009 K, the reference cell potential of 0.67 V and the stabilizing cell potential of 0.45 V. Using these sensor inputs for sensor temperature, reference cell potential and stabilizing cell potential, the sensor steady state behavior is studied to find the diffusion-rate-determined operating region. The sensor is shown to have a linear sensitivity to propane concentration from 0 to 3200 ppm. Finally, the sensor response time to different step changes from 0 up to 5000 ppm propane concentration are studied. It is shown that propane stepsize does not have a significant effect on the sensor response time. Consequently, using the working principles of an existing production amperometric NOx sensor and changing the sensor operating parameters, an amperometric hydrocarbon sensor that works in diffusion rate determining operating region is developed.