Biodiesel Fuel Effect on Diesel Engine Lubrication

Biodiesel fuel is a promising new renewable, alternate fuel source. However, its effect on diesel engine oil lubrication is largely untested at present. There is some indication that the use of biodiesel fuel can degrade diesel engine oil performance to such an extent that shortening of oil drain intervals is required. Oil which is fuel-diluted with biodiesel, which is known to contain unsaturated hydrocarbon bonds, would be expected to be more prone to oxidation. Current diesel engines designed to meet environmental standards tend to introduce more soot into the crankcase oil. The new diesel engine oils for use with biodiesel fuel must be capable of dispersing soot to minimize soot-induced viscosity increase of the oil and prevent engine wear. Oils will also need improved oxidation and corrosion inhibition. To examine soot-handling, ASTM D 7156 Mack T-11 engine test results with 20 wt% soy methyl ester in ultra-low sulfur diesel fuel (B20) were employed. The soot generated from these tests was also characterized for hardness and size and compared to soot formed from other fuels. Additional API CJ-4 engine tests were run to evaluate oxidation, deposit formation and wear, using biodiesel fuel, which meets the ASTM D 6751 quality level. Results of our studies using B20 fuel show (1) passing engine test data is obtained for soot-induced viscosity thickening, oxidation and wear, however, (2) deposits increase and (3) oxidation increases significantly when using biodiesel fuel-diluted engine oil.