Diesel soot interacts with the engine oil and leads to wear of engine parts. Engine oil additives play a crucial role in preventing wear by forming the anti-wear film between the wearing surfaces. The current study was aimed at investigating the interactions between engine soot and oil properties in order to develop high performance oils for diesel engines equipped with exhaust gas re-circulation (EGR).
The effect of soot contaminated oil on wear of engine components was examined using a statistically designed experiment. To quantitatively analyze and simulate the extent of wear a three-body wear machine was designed and developed. The qualitative wear analysis was performed by examining the wear scars on an AISI 52100 stainless steel ball worn in the presence of oil test samples on a ball-on-flat disc setup. The three oil properties studied were base stock, dispersant level and zinc dithiophosphate level. Base stocks referred to as base oil#1 and base oil#2 were studied, while the other two variables were studied at two levels: High (1) and Low (-1). This resulted in a 23 matrix (8 oil blends). The effect of soot was also studied and this resulted in a 24 factorial experiment.
Results gave a clear indication that the oil's anti-wear properties were reduced in the presence of diesel soot, which could be because of an abrasive wear mechanism. The results obtained from the statistical analysis using the general linear model (GLM) procedure of the statistical analysis system package (SAS) gave a clear indication that the base stock, and dispersant level were significant on an oil's wear performance, while the effect of zinc dithiophosphate was negligible within the range of concentrations tested. The results from the ball-on-flat-disc tests showed that the wear scar diameter of soot was comparable with the wear scar diameter of alumina, which is a known abrasive, thus indicating that wear due to soot occurred due to abrasion. Further, the EDAX tests done on a soot sample indicated that there was no adsorption of anti-wear agents by the soot.