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

Exhaust gas recirculation (EGR) is an effective means to reduce NOx 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. CO2 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″-Al2O3 solid electrolyte membrane and one using a KNO2-covered Na+–β″-Al2O3 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.