Development of a Methodology to Predict Cylinder Liner Scuffing in the 6V92TA Engine Lubricant Test©

Abstract

The requirements placed on lubricating oils at the top ring reversal point are becoming increasingly severe due to recent changes in engine technology, most of which are driven by emissions regulations. As a result, revised engine tests to evaluate cylinder liner scuffing are being introduced to engine oil specifications. Despite the high cost and generally poor repeatability of ,full-scale engine data, no laboratory screener test is commercially available. In the present study, various lubricant characteristics were correlated with the level of scuffing in the Detroit Diesel 6V92TA engine test. Good initial agreement was obtained with lubricant volatility measured at 525'C, which is predicted to be (he approximate contact temperature under the most extreme conditions likely to exist during normal operation. Measurement of lubricant volatility, howevec yields no indication of additive response and also appears to become less accurate when applied to unconventional basesrocks. As a result, a laboratory-scale wear rest was developed to predict scufing resistance under high stress conditions. The results of the wear and volatility rests are combined using a simple equation to form the Diesel Engine Oil Scuff Test (DEOST). The resulting methodology provides an R' correlation of70 percent with scuffing measured in the 6V92TA engine and is sensitive to both basestock characteristics and ontiwear additives. In addition, the DEOST results indicated that viscosity index improvers provide little benefit under hightemperature operation, an effect commonly observed by failure of petroleum-based multigrade oils in the 6V92TA engine test.