Differentiation between ‘good’, ‘borderline’, and ‘poor’ ASTM lubricant standards by ring zone sampling and multivariate data analysis

Abstract

The relative degradation of lubricant formulations corresponding to ASTM sequence IIIF and VG, ‘good’, ‘borderline’, and ‘poor’ test lubricants was investigated by piston ring zone sampling from an operating petrol engine over 25 hour test runs. Chemical/physical analyses of the lubricant samples for each formulation gave a data base that was examined by several multivariate techniques. Very clear separation is obtained between the ‘good’, ‘borderline’, and ‘poor’ lubricant formulations. Further analyses of base oil and additive pack contributions to the data base show that the ‘good/pass’ lubricant formulation maintains a close cohesive grouping of physical and chemical properties throughout the test. The ‘poor/fail’ lubricant formulation properties move towards the ‘good/pass’ formulation as the test proceeds. The ‘borderline’ lubricant formulation loses additive pack effectiveness after ∼ 60 per cent of the test duration, thereafter giving erratic database result ‘outliers’. Ring zone sampling of lubricant formulations, their chemical/physical analyses together with chemometrics is an effective, rapid, and cost effective method for separating the ASTM sequence III and V performance levels of ‘good’, ‘borderline’, and ‘poor’ lubricant formulations.