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

严格的排放法规要求开发新的废气后处理系统。它们的功能必须在船上进行监控(所谓的车载诊断；OBD)。换句话说，汽车催化剂的转化必须在操作员的监督下进行。为此，废气传感器(如果可用)用于确定催化剂下游气体成分的浓度。由此产生的问题是，这种传感器的灵敏度和/或选择性较差，并且需要来自催化剂上游侧的参考值来进行转化率计算。它的工作原理与待测气体组分的上游浓度无关，其基本思想是使用两个电极，这两个电极由离子导电陶瓷材料连接，但与不同的气体气氛接触。一个电极与被监测催化剂的上游侧接触，另一个电极与被监测催化剂的下游侧接触。传感器信号(以电压测量)是出现在每个电极上的两个混合电位之间的差值。假设混合电势与每个电极上的气体浓度呈对数关系，可以推导出传感器信号直接依赖于转换率，而与上游气体浓度无关。这一想法可以在初步试验中得到部分验证。然而，有几个问题仍然悬而未决，特别是如果混合电势偏离对数行为会发生什么，特别是对于非常小的浓度(这是催化剂下游处于高转化率状态的情况)。为此目的，缺少理论描述以及信号与入口气体浓度无关的证据。该项目应包括基础研究和实验，以显示该原理在示范应用中的潜力。还应考虑在一个设备内检测不同组件的问题。

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.