Understand effects of low temperatures on biodiesel

By John Nowatzki, NDSU Extension Service
Saturday, March 3, 2007 5:25 PM CST

Biodiesel users in cold climates need to understand the effects of low temperatures on biodiesel and biodiesel blends in diesel engines. Two characteristics, the cloud point and the cold filter plugging point (CFPP), commonly characterize the low temperature operability of diesel fuel and are equally important with biodiesel.

The cloud point is the temperature of the fuel at which small, solid crystals are visually observed as the fuel cools. CFPP is the temperature at which a fuel will cause a fuel filter to plug due to fuel components that have begun to crystallize or gel.

Commercially available biodiesel generally is a blend of petroleum diesel and biodiesel. Common blends are B2, B5, B10 and B20, with the numbers indicating the percentage of biodiesel in the blend. Studies funded by the National Biodiesel Board indicate that blends of B2 or B5 have minimal or no effect on cold-flow properties of the finished blend.

B20 that is not treated with anti-gelling additives freezes about 3 to 5 degrees Fahrenheit faster than No. 2 petroleum diesel, depending on the cold-flow properties of the biodiesel and the cold-flow properties of the petroleum diesel.

In cold-weather situations, biodiesel and No. 2 diesel can be mixed with No. 1 diesel to reduce the temperature at which gelling will occur. Biodiesels made from various crop oils have unique cold-weather characteristics that can vary up or down by as much as 5 degrees.

The cloud point of soybean biodiesel is about 30 degrees, while the cloud point for No. 1 diesel is about minus 35 degrees. Usually, when the fuel nears the cloud point temperature, changes will need to be made to the fuel, such as the addition of anti-gel additives or No. 1 diesel fuel. Otherwise, filters will clog and stop the engine.

Mixing No.1 diesel fuel with biodiesel will help reduce most fuel gelling problems. Other measures may include the addition of fuel-line heaters or in-tank fuel heaters, along with the use of anti-gel additives. Insulating the fuel filters and fuel lines from the cold also will help. These measures should eliminate most cold-weather operational problems associated with biodiesel.

The above recommendations assume that the fuels meet American Society of Testing and Materials (ASTM) specifications. ASTM is the recognized standard-setting body for fuels and additives in the U.S. ASTM has adopted a specification for biodiesel with the designation ASTM D 6751.

This specification covers pure biodiesel (B100) for blending with petroleum diesel at levels up to 20 percent by volume. The ASTM specification for petroleum diesel is ASTM D 975. Biodiesel that meets the American Society of Testing and Materials specifications is a safe and reliable fuel that can be used in most diesel engines. However, it is important to check with engine manufacturers about any impact of biodiesel use on engine warranties.

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