Engine Oil Additive Effects on the Deterioration of a Stoichiometric Emissions Control (C-4) System

Phosphorus, originating from the commonly used engine oil additive zinc dialkyldithiophosphate (ZDP), contributed to the deterioration in the performance of a stoichiometric emissions control system. Data obtained from a series of 200-hour engine-dynamometer tests suggest two separate means for phosphorus-induced system deterioration: reduced CO, NO_x, and HC conversion efficiencies due to catalyst poisoning; increased oxygen sensor rich-to-lean response time and altered oxygen sensor output voltage due to sensor contamination. The presence of an alkaline metal detergent in the ZDP-containing engine oil resulted in less deterioration of converter HC efficiency, but had no effect on the other system performance parameters.