Characterising the effects of simultaneous water and gasoline dilution on lubricant performance

Abstract

The introduction of hybrid electric vehicles presents new operating conditions which can increase water and fuel dilution of the engine oil. The effects of this type of simultaneous water and fuel dilution are poorly understood. Therefore, here we have characterised its effects on 1) boundary film performance 2) Lubricant rheology and film thickness. This is achieved by testing four samples: 0W‐20, 0W‐20+gasoline blend, 0W‐20+H20 water-in-oil emulsion and 0W‐20+H20+gasoline water-in-oil emulsions. A blended gasoline surrogate was used with a composition matching that found in real used engine oils.Gasoline dilution reduces viscosity under all conditions in a predictable fashion but has negligible chemical effects. Meanwhile, water affects only low-shear/low-pressure viscosity and is surface active and thus affects antiwear film formation by an apparent competition for the surface. This results in thinner and smoother anti-wear films giving both lower friction and higher wear. These individual behaviours are largely maintained even when water and gasoline dilution are present in the same blend, suggesting negligible interaction between the two components.