Integrating nitrogen oxide sensor: A novel concept for measuring low concentrations in the exhaust gas

In order to meet the future emissions regulations, nitrogen oxides (NOx) sensors with a high sensitivity in the low ppm detection range will be required. An integrating NOx sensor concept is proposed for that purpose. In this concept, well-known lean NOx trap (LNT) materials applied on an interdigitated electrode structure are used to accumulate the very low NOx-concentrations downstream of the NOx aftertreatment systems. When operated at 350 °C, the impedance decreased with increased NO storage. We demonstrate that the electrical impedance of such a sensor is a good measure for the amount of stored NO (verifying the integrating properties of the sensor device and its ability to detect very low amounts of NO). Moreover, first sensor tests concerning the cross sensitivity to oxygen and carbon dioxide were conducted. The data presented show that there is no significant influence of the concentration of oxygen and carbon dioxide in a wide range, but it is essential that oxygen is present at all.