Fuel and water contents are inevitable in automotive engine oils. This study intends\nto investigate the impact of the addition of gasoline (3â??20%) and water (1%) on the lubricating\nperformance of synthetic base oil (PAO), with or without an anti-wear additive (ZDDP), for a\nsteel-cast iron contact. Fuel-added PAO showed an increase in the load carrying capacity. Oil electrical\nconductivity and total acid number (TAN) measurements showed slightly increased conductivity\nand marginally increased acidity at a higher fuel concentration. In contrast, an increased wear\nrate, proportional to the fuel concentration, was observed in a prolonged test with constant-loading.\nResults suggested that the fuel addition is a double-edged sword: reducing the scuffing risk by\nproviding stronger surface adsorption and increasing the sliding wear rate by bringing down the\noil viscosity. The PAO-water blend formed an emulsion and resulted in a significantly increased\nload-carrying capacity, again likely due to the higher polarity and possibly acidity. For the\nZDDP-containing PAO, the addition of 1% water and 3% fuel generated 24% and 52% higher wear.\nThe phosphate polymerization level was reduced on the worn surfaces by the introduction of water\nbut the thickness of ZDDP tribofilm was not significantly affected.
Loading....