Selective ammonia exhaust gas sensor for automotive applications

In order to meet future NOx emission standards for commercial vehicles, so called urea selective catalytic reduction (SCR) systems will be introduced. In the SCR converter ammonia serves as a reducing agent for selective NOx reduction. An ammonia exhaust gas sensor is required to optimize the injected amount of urea and to assure that no ammonia emissions occur. This paper reports on the development of a selective thick film ammonia sensor that can meet the requirements for applications in automotive exhaust gas. Main topic is the development of the functional gas sensitive film. Zeolites were successfully investigated as selective functional materials for this kind of sensors. It is shown, that the type of the zeolite, its module, the working temperature and the working frequency determine sensitivity and selectivity of the sensor. From the most promising zeolite material—zeolite H-ZSM5 with a module of 140, sensors were manufactured and tested in engine test benches. It could be shown, that this kind of sensors is a useful tool to control an ammonia-SCR system and to detect ammonia slip.