Biodiesel Lubricity

The need to reduce the exhaust emissions of diesel engines has driven the development of new diesel engine technology. These innovations have focused on the development of: 1) diesel fuel injection technology, 2) exhaust after-treatment technology, and 3) diesel fuel that has been refined to higher standards. The diesel fuel injection technology of a modern diesel engine operates at higher pressures than its counterparts (1). This new technology has demanded better lubrication from the diesel fuel that has traditionally lubricated the fuel injection system of the diesel engine.

Prior to October 1993, the diesel fuel that was sold in the US had a sulfur level of approximately 5000 ppm. In 1993, the Environmental Protection Agency (EPA) mandated that all diesel fuel sold in the US contain 500 ppm or less sulfur. The petroleum refineries, largely due to special hydrotreating of the diesel fuel, produced a cleaner diesel fuel that met this requirement. On June 1, 2006 the EPA will again lower the level of sulfur in petroleum diesel fuel. The new standard will be 15 ppm. This reduction of sulfur is projected to reduce diesel engine exhaust emissions by as much as 90% when compared to the 500 ppm low sulfur diesel fuel era. The reduction in engine exhaust emissions is projected for new diesel engines that are equipped with diesel engine exhaust catalytic converters.

Research has demonstrated that catalytic converters last longer, aromatic hydrocarbon emissions are lower, and oxides of nitrogen emissions are lower when cleaner fuels are burned in diesel engines. Unfortunately, the hydrotreating that was used to reduce the sulfur produced a fuel that sometimes failed to provide adequate lubrication for the fuel injection system of the diesel engine.

Lubricity analysis using the SLBOCLE and HFRR test procedures have indicated that the new 15 ppm low sulfur diesel fuel will exhibit lower lubricity than found in 500 ppm diesel fuel. Engine manufacturers have proven that a single tankful of diesel fuel with extremely low lubricity can cause the diesel fuel injection pump to fail catastrophically.

Research conducted using 1-2 percent blends of biodiesel mixed with petroleum diesel fuel revealed an increase in lubricity. HFRR test procedures using a two percent blend of
biodiesel reduced the wear scar diameter by nearly 60 percent (from 513 to 200 microns).