Sensor for direct measurement of the conversion of an automotive exhaust gas catalyst

点击翻译按钮获取中文摘要

Stringent emission legislation demands the development of novel exhaust gas aftertreatment systems. Their functionality has to be monitored on board (so-called on-board-diagnostics; OBD). In other words, the conversion of automotive catalysts has to be monitored in operando. For that purpose, exhaust gas sensors (if available) are in use to determine the concentration of gas components downstream of a catalyst. Problems hereby are poor sensitivity and/or selectivity of such sensors and the need of reference values from the upstream side of the catalyst for conversion calculation.The present project deals with a novel sensor that measure directly catalyst conversion. It works independently from the upstream concentration of the gas component to be determined.The basic idea is to use two electrodes which are connected by an ion conducting ceramic material but are in contact with different gas atmospheres. One electrode is in contact with the upstream side and the other one with the downstream side of the catalyst to be monitored. The sensor signal (measured as a voltage) is a difference between two mixed-potentials appearing at each electrode. Assuming (as a simplification) a logarithmic relationship between the mixed-potentials and the gas concentrations at each electrode, one can derive that the sensor signal depends directly on the conversion rate and that it is independent from the upstream gas concentration.This idea could be verified partly in preliminary tests. However, several questions remain open, in particular what happens if the mixed-potential deviates from the logarithmic behavior, especially for very small concentrations (this is the case downstream of the catalyst in a state of high conversion). A theoretical description is missing for that purpose as well as the proof that the signal is independent from the inlet gas concentration.The project shall include elementary investigations as well as experiments to show the potential of such principle for exemplary applications. The question of detecting different components within one device should be also regarded.