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Moos, Ralf:
Ceramic Exhaust Gas Sensors : Recent Developments.
2017
Veranstaltung: 8th International Conference on Electroceramics (ICE2017)
, 28.-31.05.2017
, Nagoya, Japan.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung
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Vortrag
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Abstract
Nowadays, exhaust gas sensors are installed in quantities of millions in catalytic automotive exhaust gas aftertreatment systems. Only few sensor materials are reliable enough to withstand the harsh exhaust conditions. Stabilized zirconia combines oxygen ion conductivity, which is required for the sensors’ functionalities, with high strength. Originally produced in classical ceramics technology, most exhaust gas sensors are now produced in ceramic tape and thick-film technology. At first, this contribution outlines very briefly the history of zirconia-based exhaust gas sensors, starting from the binary lambda-probe, the wideband lambda probe and the NOx sensor to the recently introduced ammonia sensor. It is also shown how the development of exhaust gas sensors has always to be considered in interaction with exhaust gas aftertreatment systems. This elucidates why novel kinds of sensors have gained in importance just recently when stricter emission regulations were announced, meaning that time was ripe for novel exhaust gas aftertreatment concepts. Another driver for the sensor development are the requirements to detect failures of components of the exhaust gas aftertreatment system directly during car operation (on-board diagnostics; OBD). The recently introduced ceramic soot sensor, which indicates already low amounts of soot in the exhaust, as they appear when diesel particulate filters (DPF) are malfunctioning, is an example for that. Its sole purpose is to diagnose the correct effectiveness of a DPF. Another recently suggested ceramic sensor for OBD, which is in the research stadium, indicates directly the conversion of a distinct gas species. Based on and explainable by the mixed potential theory, the sensor compares the exhaust up- and downstream of a catalyst. The electrode material selects the selectivity. The sensor response correlates well with a theoretically derived semi-logarithmical dependence on the catalyst conversion, and interfering effects cancel out each other. The sensor itself consists of a self-heated yttria-stabilized zirconia disc that is hot enough for sensing in the central region and cold enough at the outer radius for contacting why novel kinds of sensors have gained in importance just recently when stricter emission regulations were announced, meaning that time was ripe for novel exhaust gas aftertreatment concepts. Another driver for the sensor development are the requirements to detect failures of components of the exhaust gas aftertreatment system directly during car operation (on-board diagnostics; OBD). The recently introduced ceramic soot sensor, which indicates already low amounts of soot in the exhaust, as they appear when diesel particulate filters (DPF) are malfunctioning, is an example for that. Its sole purpose is to diagnose the correct effectiveness of a DPF. Another recently suggested ceramic sensor for OBD, which is in the research stadium, indicates directly the conversion of a distinct gas species. Based on and explainable by the mixed potential theory, the sensor compares the exhaust up- and downstream of a catalyst. The electrode material selects the selectivity. The sensor response correlates well with a theoretically derived semi-logarithmical dependence on the catalyst conversion, and interfering effects cancel out each other. The sensor itself consists of a self-heated yttria-stabilized zirconia disc that is hot enough for sensing in the central region and cold enough at the outer radius for contacting and plastic sealing.