Comparing Bio-oils for Use
as Biodiesel Fuel

Numerous bio-oils can be used to produce biodiesel fuel but these oils have some different performance characteristics in agricultural tractors and self-propelled machines. These characteristics, which differ from the standard petroleum diesel fuel, include cetane rating, lubricity, pour point, and cloud point. The oil production, gallons per acre, resulting from the various crops vary a great deal.

The primary Midwestern US and Central Canada crops considered for production of biodiesel are canola, sunflowers, safflowers and soybeans. This discussion will include corn because the oil is a potential by-product of the ethanol process or other processes.

Oil production per acre will be dependent on the seed yield and the oil content of the seed
and will vary from year to year. Using average yield data, canola produces the greatest quantity of oil per acre (127 gallons) followed by sunflowers, safflowers, soybeans and corn in that order, see table. Corn has the lowest production per acre (18 gallons).

Cetane rating describes the ignition characteristics of diesel fuel. Fuels with higher rating will cause an engine to operate more efficiently and will tend to start more easily. Most petroleum diesel fuels on the market range from 40 to 55. The biodiesel fuels have higher ratings than the standard petroleum diesel fuels, see table. The differences among the biooils are small, see table, with canola being slightly higher.

For older engines, a minimum cetane rating of 40 is recommended. For modern tractors, one manufacturer recommends a minimum cetane rating of 45 but 50 is preferred. The ratings for biodiesel are above the preferred rating which should not create a problem.

Cloud point is the temperature where the wax crystals become visible in the fuel. One tractor manufacturer recommends the cloud point should be ten degrees Fahrenheit below the coldest temperature. The cloud points for biodiesel will create problems for temperatures in Ontario, see table. These crystals will plug the fuel filter. The pour point is the temperature where the fuel is no longer pumpable, resulting no fuel being delivered to the engine, leaving it inoperable. Sunflower oil exhibits the highest cloud point, 45 degrees Fahrenheit, see Table 2 .

* Similar to Canola
** Similar to Diesel Fuel #1

If 100 percent biodiesel is going to be used, at least two solutions are available to address the cloud and pour point problems. Heating the fuel to a temperature about ten degrees above the pour point will reduce the problem but would require modifications to the engine and its fuel tank. Additives are on the market for lowering the cloud and pour points of diesel fuel. The additives may be referred to as pour point depressants or antigels. Based on market information on fuel additives, there appears to be some additives developed specifically for the biodiesel fuels.

The energy available in each pound of biodiesel fuel is eight to ten percent less than petroleum diesel fuel, see table. The density of biodiesel is about four to five percent greater than the petroleum diesel fuel. Therefore the difference is less when considering the energy in a gallon of fuel but the biodiesel fuel is slightly less efficient. Under normal engine loads, the operator may not perceive a difference in engine performance when switching to biodiesel due to the small difference.

Lubricity is the ability of the diesel fuel to lubricate the fuel pump and injectors where parts are close fitting. Biodiesel fuel has higher lubricity characteristics and can be used to improve petroleum fuels. A blend of one to two percent of biodiesel with petroleum diesel will greatly improve its lubricity. Adding more biodiesel will have little impact on the lubricity of the blend.

Biodiesel oils from the various crops are very similar with respect to efficiency, cetane rating and lubricity. Some of the biodiesel fuels have higher cloud and pour points, making them more undesirable for Ontario operation unless additives are used or engines modified. The greatest difference among the various sources of biodiesel fuel is the production per acre, where canola is the highest. The importance of these differences will be impacted by the uses of by-products from the manufacturing of the biodiesel fuel and the availability of the crop.

Information sources:

Auld, D. L., B. L. Bettis and C. L. Peterson. 1982. Production and Fuel Characteristics of Vegetable Oilseed Crops in the Pacific Northwest. Vegetable Oil Fuels, Proceedings of the International Conference on Plant and Vegetable Oils. ASAE, pp.92-100.

Kurki, A., A. Hill, and M. Morris. 2006. Biodiesel: The sustainability dimensions. Accessed September 29, 2006.

Life Cycle Inventory of Biodiesel and Petroleum Diesel. NREL/SR-580-24089. Accessed October 3, 2006

Schuler, R. T. 2006. Biodiesel Fuels in Agricultural Equipment, Wisconsin Crop
Manager, vol. 13, no.21, Aug 13, 2006

Related Links

• Biodiesel: The sustainability dimensions

• Life Cycle Inventory of Biodiesel and Petroleum Diesel

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