Since Oct. 15, 2006, most diesel fuel sold at retail locations in the U.S. is ultra-low sulfur diesel fuel (ULSD) that has different lubricating qualities than diesel previously available.

“ULSD diesel fuel has substantially reduced levels of sulfur,” says John Nowatzki, North Dakota State University Extension Service agricultural machine systems specialist. “The reason for lowering the sulfur content is to allow the application of newer engine emissions control technologies. This will substantially lower emissions of nitrous oxide and particulate matter emissions to the atmosphere. However, the process used to reduce the sulfur content in diesel also reduces the fuel's lubricating properties, resulting in increased wear on the various parts of the engine's fuel injection system.”

Government regulations controlling the sulfur content of diesel fuels only mandate that ULSD diesel be used for highway use.

“However, most of the diesel available for farm use in 2007 and later also will be ultra-low sulfur diesel,” Nowatzki says. “Farmers need to know the sulfur content of the fuel they are using. Ultra-low sulfur diesel contains 15 parts per million of sulfur.”

Diesel fuel retailers are required to document the sulfur content of the fuel they sell. Retailers also will know the type and amount of lubricating additives in the fuel they sell, so farmers can ask their supplier for the sulfur content and additives in the fuel delivered to their storage tanks.

Diesel fuel producers recognize the issues associated with the lower lubricating characteristics of ULSD, so they are including lubricating additives in retail diesel fuel. Some suppliers are blending biodiesel, which has excellent lubricating characteristics, with petroleum diesel.

“To manage the change in the lubricating qualities of diesel fuel, the American Society for Testing and Materials (ASTM) adopted the lubricating specification defined in ASTM D975 for all diesel fuels,” Nowatzki says. “The ASTM D975 standards specify the minimum lubricating characteristics of No. 1 and No. 2 diesel fuel, but do not specifically address petroleum diesel blends with biodiesel. Also, No. 1 diesel, commonly available during winter in the northern parts of the U.S., generally has less lubricating ability than the higher viscosity No. 2 diesels.”

The ASTM D975 standards for lubricity set the maximum amount of wear on materials when tested with specific fuels or blends of fuels. The test apparatus is called a High Frequency Reciprocating Test Rig (HFRR). Both No. 1 and No. 2 diesel test results cannot exceed 460 microns of wear when tested in a HFRR. A lower wear score indicates better lubricity. Biodiesel has been tested at varying concentrations with No. 1 and No. 2 diesel fuels. The results indicate that a 1 percent blend of biodiesel with No. 2 diesels is sufficient to reduce the HFRR micron score below the required 460 micron standard. However, a 2 percent biodiesel blend is required in No. 1 diesel to get the HFRR micron score down to 460 microns.

The National Biodiesel Board states “even low blends of biodiesel are highly effective at enhancing the lubricity of diesel fuel. The typical blend used for lubricity enhancement is 2 percent biodiesel mixed with 98 percent diesel.” Other diesel fuel lubricating additives are readily available, but are expensive if added at the manufacturers’ recommended rates.

Biodiesel and biodiesel blends are becoming more widely available across the U.S. To get up-to-date information on where it is available, check the Web site for the National Biodiesel Board at http://www.biodiesel.org/. Click on Guide to Buying Biodiesel. Under the heading of Locate Distributors in the U.S, click on “Click here for a National Map of Biodiesel Distributors.” Then click on a specific state on the map. Make sure that you are buying biodiesel and not crude, unprocessed vegetable oil. Ask the distributor to provide certification that the biodiesel meets ASTM D975 standards.

NDSU Agriculture Communication