Effect of Viscosity Index Improvers in Ethanol/Gasoline/Water Emulsions Formed with E25 and E85 in Passenger Car Motor Oils

Concern about the consequences of fuel dilution on engine oil properties are intensifying due to the increasing use of E25 and E85 fuel in passenger cars. Notably, such concerns are about the effect of emulsion formation and stability in crankcase oils by E25 or E85 fuel and water dilution on vehicle operation at cold-start conditions. Different types of Viscosity Index Improver (VII) chemistries were evaluated for their effects on emulsion formation and engine oil characteristics. Emulsions were prepared with fresh and used passenger car motor oils using the ASTM D7563 method for emulsion retention. The emulsion properties were evaluated after storage for 24 hours at two different temperatures. Separate oil/gasoline and emulsion (ethanol/water/oil) phases were observed for fresh oil emulsions. None of the emulsions exhibited a separate water phase, regardless of the type of VII in the oil. Analysis of the emulsion composition by Fourier Transform Infrared spectroscopy and Gel Permeation Chromatography confirmed ethanol and water were present in the emulsion phase, while the gasoline and other oil soluble components, including the VII, were present in both phases. When used field test oils were assessed for their emulsion characteristics with E85/water, the used oil emulsions formed a single emulsified phase. This was in contrast to fresh oil behavior. Both fresh and used oil emulsions were tested in a Cold-Cranking Simulator, and Mini-Rotary Viscometer. The results confirmed that the low temperature emulsified oil properties were independent of the type of VII used in the formulation.