Integrating NO_x Sensor for automotive exhausts-A Novel concept

Emissions regulations concerning NO_x are getting increasingly stringent. Thus, new technologies are being developed for the reduction of N0X in the exhaust pipe, especially for modern diesel and lean-burn gasoline vehicles. To meet the requirements of the On-Board Diagnosis (OBD) the correct function of all components of the exhaust aftertreatment system have to be controlled. For that challenge NO_x sensors with a high sensitivity and a sufficient accuracy in the low ppm detection range for the detection of the reduced NO_x emissions downstream of catalytic converters are required. We propose a novel gas sensor concept to fulfill this need: instead of detecting the actual N0X concentration instantaneously, the N0X molecules will be accumulated on an integrating NO_x sensor device and the integrated amount of the analyte will be measured. By integration or summing up, this sensor is able to detect very low amounts of N0X. In first tests, a lean NO _x trap (LNT) material was used successfully as sensitive layer collecting the analyte molecules from the gas. The integrating properties of these sensor devices were confirmed several times and it was shown that the instantaneous NO_x concentration by itself was not influencing the sensor signal, rather its total accumulation over time. In first tests the cross sensitivities to oxygen and carbon dioxide were found to be negligible. The influence of the sensor temperature on the sensor performance was investigated. By varying the operating temperature in a wide range the effect on the sensitivity and on the measurement range of the integrating sensor were monitored.