(339c) Effect Of Major And Minor Components Of Biodiesel On The Lubricity Of Petroleum And Synthetic Fuel

Authors: 
Wadumesthrige, K., National Biofuel Energy Laboratory, Department of Chemical Engineering, Wayne State University
Wang, A., Wayne State University
Salley, S. O., Wayne State University
Ng, K. Y. S., Wayne State University


Increasingly strict regulations on the sulfur content of commercial petroleum diesel fuels as required by the United States, Europe, and elsewhere, result in a decrease in the lubricity of these fuels. This has led to the failure of engine parts such as fuel injectors and pumps, because they are lubricated by the fuel itself. The poor lubricity of ultra low sulfur diesel (ULSD) requires additives or blending with another fuel of sufficient lubricity to regain lubricity. Previous studies indicate that low blend levels (1-2 %) of biodiesel derived from vegetable oil can restore lubricity to (ultra-)low-sulfur petroleum-derived diesel. In this work, the lubricity effects of major components of biodiesel (fatty acid methyl esters) and minor components such as antioxidants, phospholipids, Sterols, free fatty acids and glycerol compounds on ULSD, and synthetic fuel, S-8 were studied using High Frequency Reciprocating Rig (HFRR) and Scuffing Load Ball On Cylinder Lubricity Evaluator (SLBOCLE) test methods. Systematic study using distilled biodiesels of various feedstocks reveled that blending distilled biodiesel cannot increase the lubricity of ULSD and S-8 as compared to blending with undistilled biodiesel. Adding minor components present in biodiesel especially polar phospholipids can increase the lubricity of ULSD and S-8 considerably. The effects of individual biodiesel components with various chemical and physical properties on diesel lubricity were also examined and used to develop an empirical mathematical formula to predict biodiesel lubricity. HFRR lubricity measurements were performed at 60 ºC according to ASTM D-6079 test method and SLBOCLE measurements were performed at 25 ºC and 50% relative humidity as described in ASTM D-6078 test method. The severely hydrotreated ULSD has a HFRR mean wear scar diameter (WSD) of 430 µm and a SLBOCLE maximum load of 3200 g; while the synthetic fuel, S-8, has a HFRR mean wear scar diameter of 679 µm which is much higher than the Diesel Fuel oil specification as well the requirement for Engine Manufactures Association (EMA). Blending both ULSD and S-8 with up to 2% v biodiesel shows a sharp decrease of WSD. The WSD levels off at around 200 µm regardless of the type of fuel or the type of blending biodiesel. This constant 200 µm value may be due to the formation of a uniform lubricating layer at metal-metal contact interface. Further addition of biodiesel did not show any further lubricity improvement In order to elucidate the origin of biodiesel lubricity, several major and minor components present in biodiesel were added to ULSD and S-8. With 2 % v of the Methyl ester of linoleic acid, the lubricity of ULSD was increased only by 12% (calculated based on % wear scar diameter reduction); whereas 2% of biodiesel can improve ULSD lubricity by about 50%. Interestingly, vacuum distilled biodiesel with no minor components such as sterols, antioxidants and phospholipids only improved the lubricity of ULSD by 28%. The lubricity enhancement mechanism of these minor components will be discussed. These results will help to develop better and reliable lubricity improves for commercial applications.