A Reliable Potentiometric NOx Sensor

The NO_x/O₂ sensor has been developed based on a simple tubular design. It is a potentiometric sensor that gives out two sensor voltages: one for the O₂ concentration, the other for the NO_x concentration. The NO_x sensor has been extensively tested in synthetic gases and in real exhaust gases. It gives a good response towards NO_x and NO₂ for O₂ concentrations between 0.5 and 20.8%. The sensor can be used to detect NO_x in the range from 10-1500 ppm. Typical gas lab measurements to check the sensitivity and cross-sensitivity are shown. Succesfull sensor testings before and after a lean NO_x trap (LNT) on a GDI engine are performed. The sensors are also tested on an exhaust gas simulator to check their sensitivity towards NO in more realistic circumstances. The fact that this is a potentiometric sensor has important advantages, e.g. the simple design, the better sensitivity towards low NO_x concentrations, the good long term stability and the easy signal processing because of the voltage signals. This sensor is ideally suited for the monitoring and control of different kinds of NO_x catalysts and/or for the measurement of raw NO_x emissions in exhaust systems.