Overview on recent developments on engine control by radio-frequency-based catalyst and filter monitoring

摘要

The state of catalysts and filters plays a key role in automotive exhaust gas aftertreatment. The soot or ash loading of particulate filters (GPF, DPF), the amount of loaded oxygen in three-way catalysts (TWC), the amount of stored ammonia in SCR catalysts, or the NO_x loading degree in lean NO_x traps (LNT) are important parameters. Today, they are determined indirectly and/or model-based calibrated by gas sensors installed up- or downstream of the catalysts or by a differential pressure sensor. This contribution gives an overview on a promising novel approach to determine directly the catalyst state by a microwave-based technique. For that purpose, the catalyst housing serves as a cavity resonator. As "sensing" element, one or two simple antennas are mounted in the catalyst canning. The electrical properties of the catalyst device (ceramic honeycomb incl. coating and storage material) can be measured. Such contactless-obtained information is very well correlated with the catalyst state as will be demonstrated for different systems like SCR catalysts, TWC, DPF, coated GPF or LNT. Even control is possible without additional gas sensors.