Effect of diesel soot contaminated oil on engine wear - investigation of novel oil formulations

Exhaust Gas Re-circulation (EGR) has been found to be very effective in red ucing emissions of oxides of nitrogen, for light duty diesel engines. Howev er, EGR results in a sharp increase in particulate matter emissions in heav y-duty diesel engines. The effects of soot contaminated engine oil on wear of engine components wa s examined using a statistically designed experiment. The three oil propert ies studied were phosphorous level, dispersant level and sulfonate substrat e level. The above three variables were formulated at two levels: High (1) and Low (-1). This resulted in a 2(3) matrix (eight oil blends). The effect of soot was also taken into consideration, which resulted in a 2(4) factor ial experiment. A three-body wear machine was designed and developed to simulate and estima te the extent of wear. Ball-on-flat-disk tests were conducted to qualitativ ely study wear by comparing wear scars due to soot with wear scars due to a known abrasive (alumina). A Scanning Electron Microscope (SEM) was used to study the microstructures of the wear scars. Surface chemical analysis was performed on soot particles and wear scars using Energy-Dispersive X-ray A nalysis (EDAX). Results show that diesel soot interacts with oil additives reducing the oil 's anti-wear properties possibly by abrasive wear mechanism. Statistical an alysis (GLM) showed that the phosphorous level plays a dominant role on oil 's wear performance. The effect of dispersant level was not very significan t, though on an average, higher dispersant levels reduced wear. The effect of sulfonate was not revealed within the range of these concentrations. Bal l-on-flat-disk type tests also revealed the increased wear due to the prese nce of soot. SEM studies of Wear Scar Diameters suggest that soot is abrasi ve. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.