Oxygen sensors for cylinder-selective measurement of the lambda value in motor vehicle engines are exposed to extreme environmental conditions. At the mounting position close to the cylinder outlet valve, temperatures up to 1000 °C prevail, as well as vibrations > 50 g and powerful turbulent flows that are loaded with particles from the engine wear and with contaminants from engine oil and fuel. Thin-film oxygen sensors made from metal oxides, which function in a completely satisfactory and stable way in extensive laboratory experiments, already show significant signs of degradation during engine operation after a relatively short time (10 h). This paper discusses, for the first time in detail, experimental results on the degradation of thin-film oxygen sensors in motor vehicle engines and its concrete causes. For this purpose, comprehensive studies with surface and microanalysis methods (Auger electron spectroscopy, X-ray fluorescence analysis, X-ray photoemission spectroscopy, electron microprobe and optical microscopy) have been performed and correlated with changes in the sensor characteristics. The results show that both doping of the sensor material by contaminants from oil and fuel and deposition of particles from engine wear on the sensor surface give rise to changes in the sensor characteristic. An improved sensor housing reduces the particle deposition and thus contributes to a significant increase in the long-term stability of the fast lambda probe.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Surfaces, Coatings and Films
- Metals and Alloys
- Electrical and Electronic Engineering
- Materials Chemistry