Biodiesel Fuels in Agricultural Equipment

Ronald T. Schuler, Extension Agricultural Engineer, University of Wisconsin-Madison

During the 2006 Wisconsin Farm Technology Days, biodiesel fuel was used in the engines of field demonstration machines with no apparent problems in any of the engines. A blend (B5) of five percent biodiesel and ninety-five percent diesel fuel was used. US farm machinery manufacturers and fuel suppliers indicate that this blend (B5) of biodiesel provides several advantages over straight diesel but suggest following some appropriate service and maintenance procedures when using biodiesel.

The biodiesel provides a fuel alternative that is renewable and reduces the dependency on petroleum imports. When added to diesel fuel at low levels, the cetane rating and lubricity are improved. The cetane rating is an indication of the knock characteristics of a diesel fuel, much like the octane rating for gasoline. Most diesel fuels available today have a cetane rating from 40 to 44, while the cetane rating of soy biodiesel is about 47.

Lubricity is the ability of the fuel to lubricate which is especially importance in the fuel pump and injectors where clearances between parts are very small and pressures may be rather high. Adding one to two percent by volume of biodiesel to diesel fuel significantly improves the lubricity of diesel fuel. Higher portions of biodiesel have very little impact on the diesel fuel lubricity improvement.

The biodiesel blends have reduced emissions of some pollutants but may increase others. Sulfur, aromatics and hydrocarbons emissions will be less but the nitrous oxides will increase slightly.

Other issues regarding biodiesel fuels include moisture absorption, cold weather problems, and some seal and material compatibility. All these issues become more important when using higher blends of biodiesel. Nonetheless, at the five percent level several normal recommended practices should be completed. With moisture absorption, there is an increased risk of microorganism growth in the fuel tank which may lead to an increased clogging of the fuel filters. Any steps to reduce the potential of water entering the fuel system should be followed. Examples include insuring fuel caps are properly installed, more frequently draining the water from the water trap on an engine, keeping tanks filled, including storage tanks,  and adding a water trap on the fuel storage tank to separate the water from the fuel as it is drawn from the storage tank.

During cold weather fuel clouding or wax separation may occur, especially with higher blends of biodiesel. This may lead to fuel filter clogging and hard starting. This should not be a problem with B5 but is a concern with higher levels of biodiesel.

When changing from diesel to biodiesel, more contaminants will be present in the fuel initially because the biodiesel acts as a solvent. Therefore fuel filters may need to be changed more frequently immediately after changing to the biodiesel. The filters can be changed at the normal recommended interval after several filter changes.

In closing, a five percent blend of biodiesel can be used in most new farmer tractors, which was demonstrated during the 2006 WI Farm Technology Days. But the machinery owner should check with their machinery dealer to insure the manufacturer approves its use and warranties will be honored. When using B5 biodiesel, be sure to follow a few maintenance steps especially those dealing with minimizing moisture in the fuel.