An Investigation into Lubricant Related Poisoning of Automotive Three-Way Catalysts and Lambda Sensors

This paper investigates some of the parameters involved in the mechanism of poisoning of automotive three-way catalysts and Lambda sensors by means of a purpose designed engine test procedure. The aged catalysts have been examined both in terms of their conversion efficiency and surface chemical properties by SEM and EPMA techniques. Lambda sensors were also aged in the test engine and their sensitivity to lubricant phosphorus content and exhaust gas temperature examined.

Results from 55 engine tests on 24 oils formulated with differing chemistries confirm that there is a strong link, which is statistically significant (99% confidence level), between lubricant phosphorus content and catalyst performance, but surprisingly oil consumption does not appear significant. The mechanism whereby the oil is combusted is proposed as being a determining factor. High phosphorus type oils reduced oxygen sensor performance, particularly at low exhaust temperatures (urban duty). Little or no sensor deterioration was evident when using low phosphorus oils.