The Degradation of Lubricants in Gasoline Engines: Lubricant Flow and Degradation in the Piston Assembly

摘要

The effects of engine load and speed on the level of degradation of lubricant extracted from the piston top ring zone of a gasoline engine have been examined for a partially formulated Group III base fluid with calcium alkyl sulfonate detergent; higher loads and lower engine speeds give greater levels of degradation. The degree of oxidation of the lubricant was determined by monitoring the concentration of carbonyl containing species using FTIR spectroscopy. Comparison of the level of degradation products in the piston ring pack with the rate of increase of these products in the sump allow rates to be calculated for lubricant flowing through the piston ring pack and returning to the sump; the flow rates varied little with load at 0.6 cm~3 s~(-1) cylinder~(-1) (over the range 33 -75 %) but increased proportional to engine speed from approximately 0.4 cm~3 s~(-1) cylinder~(-1) at 1000 rpm to 0.9 cm~3 s~(-1) at 2000 rpm. The effect of the calcium alkyl sulfonate detergent has also been examined; its presence substantially increases the rate of lubricant flow through the piston assembly and reduces the level of degradation of the lubricant in the piston ring pack. The nature of oxidation products containing the carbonyl group was also examined; approximately half were found to be carboxylic acids.