Effects of Lubricating Oil on Hydrocarbon Emissions in an SI Engine

The effects of lubricant composition on hydrocarbon emissions from a SI engine have been experimentally investigated. Results based on measurements of solubilities of different fuel components in different types of lubricants are presented. 2 lubricants and two hydrocarbons were chosen for testing in a single cylinder engine. Emissions and performance was measured for various fuel air ratios and ignition timings. The lubricant with the lowest solubility with respect to isooctane also showed the lowest hydrocarbon emissions. The influence of the lubricant was greatest at lean air fuel ratios. Xylene is much more soluble in the lubricants than isooctane and gave lower hydrocarbon emissions when the engine was operated at rich air fuel ratios. At leaner mixtures, isooctane gave lower emissions. The results indicate that the lubricant plays a contributing, but not dominating role in hydrocarbon emissions from gasoline engines.