Biodiesel is an excellent diesel engine fuel if it meets the American Society Testing and Materials (ASTM) standards for biodiesel, according John Nowatzki, North Dakota State University Extension Service agricultural machine systems specialist.

The ASTM standard for biodiesel, D6751, specifies the parameters for 18 biodiesel factors that affect biodiesel purity, storage, cold weather properties and use in engines. The ASTM D6751 standard is for B100, which is 100 percent biodiesel before it is blended with petroleum diesel.

""For biodiesel to consistently perform well in engines, it must be completely converted from the source vegetable oil into biodiesel and the catalysts involved in the conversion process and the coproducts completely removed,"" Nowatzki says. ""The ASTM standard provides the assurance that this has been accomplished."

Biodiesel has less energy than diesel fuel. Summer petroleum diesel fuel typically contains about 140,000 British thermal units (Btu) per gallon, while biodiesel contains about 130,000 Btu per gallon. Fuels with a higher heat of combustion (Btu content) usually will produce more power per unit of fuel than lower-energy fuels.

""As a result, an engine using a lower-energy fuel will require more fuel to produce the same power as diesel fuel,"" Nowatzki says. ""Since biodiesel has less energy, it will require about 1.1 gallons of fuel to do the same work as 1 gallon of diesel fuel. This is about an 8 percent power reduction."

Several factors influence how well biodiesel works in diesel engines. The cetane number is a method for determining the ignition quality of a fuel. Most farm tractor engine manufacturers recommend a minimum cetane rating of 40. However, most fuel suppliers provide diesel fuel with a cetane rating of 45 to 50. A typical biodiesel cetane rating is 55. In general, high-cetane fuels permit an engine to be started more easily and provides for a faster engine warm-up without producing white smoke or misfiring. A high-cetane fuel will help reduce the rate of varnish formation and carbon deposits in an engine. It also eliminates combustion roughness or engine knock.

Viscosity has an influence on the atomization of the fuel when it is injected into the engine combustion chamber. The viscosity of summer-blend petroleum diesel is generally about 3, biodiesel about 5.7 and vegetable oil about 40 to 50.

""If the viscosity is too high, excessively high pressure can occur in the injection system,"" Nowatzki says. ""This will cause poor atomization of the fuel in the combustion chamber, which may cause deposits around the piston rings. This is the case when raw or partially refined vegetable oil is mixed with diesel fuel."

Biodiesel is highly solvent and may remove deposits in the fuel system, which in turn can plug fuel filters or cause deposits to accumulate in fuel tanks. Filters generally do not continue to plug after the initial use of biodiesel. Biodiesel may cause fuel lines, gaskets and fuel pump seals on older engines to deteriorate. Seals made from materials more biodiesel-tolerant are readily available.

Since Oct. 15, 2006, most diesel fuel sold at retail locations in the U.S. is ultra-low sulfur diesel fuel that has different lubricating qualities than diesel previously available. According to diesel fuel refiners, the processing required to reduce sulfur also removes naturally-occurring lubricating agents in diesel fuel, resulting in increased wear on the various parts of the engine's fuel injection system. The ASTM D975 standards for lubrication 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 (winter blend) and No. 2 (summer blend) diesel test results cannot exceed 460 microns of wear when tested in an HFRR.

A lower wear score indicates better lubrication. 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 diesel 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. Biodiesel (B100), when used alone, provides excellent lubricity.

""There are significant issues to consider when using B100 in engines if the outdoor temperature is below 35 degrees Fahrenheit,"" Nowatzki says.

More information on using biodiesel in cold weather is available on the NDSU energy efficiency Web site at http://www.ag.ndsu.nodak.edu/abeng/energy_efficiency/.

NDSU Agriculture Communication