Sensor for directly determining the exhaust gas recirculation rate—EGR sensor

Exhaust gas recirculation (EGR) is an effective means to reduce NO x emissions of internal combustion engines without increasing fuel consumption. Up to now, only complex procedures to determine the exhaust gas recirculation rate are available. Here, a novel sensor device is suggested that measures directly at one position and with only one single sensor device the concentration of a tracer gas at the intake manifold and at the exhaust gas recirculation entry point. The tracer gas (e.g. CO 2 or NO) is formed during combustion and is only in a negligible concentration present in the fresh air. A solid ion conducting membrane constitutes the core of the sensor device and separates both gas atmospheres. The sensor voltage depends Nernst-like on the exhaust gas recirculation rate. Two types of sensors, one comprising a NO +–β″-Al 2O 3 solid electrolyte membrane and one using a KNO 2-covered Na +–β″-Al 2O 3 membrane showed a slope in the semilogarithmic plot almost as expected from theory for a single electron process. It was shown that the sensor output voltage is not dependent on the air-to-fuel ratio. Further research should address solid oxygen ion conducting membranes using a double side mixed potential principle.