Using Biodiesel

Interest in renewable energy has heightened due to uncertainties of the supplies and prices of fossil/petroleum fuels. The production of biodiesel in the U.S. is becoming increasingly more available. But biodiesel fuels have properties different from petroleum diesel which are both positive and negative with respect to engine performance.

Biodiesel can be produced from a variety of sources. In 2002, the primary world source was canola at 84%. Sunflowers were second at 13%, with soybeans and palm oil each contributing 1% to the world market. The production of biodiesel in the U.S. (primarily from soybeans) has been increasing dramatically each year since 2001. The production from 1999 to the present has nearly doubled each year.

Lubricity In Focus

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Biodiesel provides several advantages over petroleum diesel. Examples of these characteristics are lubricity, cetane rating, and fewer environmental pollutants. Let’s review these in some detail.

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Lubricity is the ability of the fuel to lubricate. This is especially important in the fuel pump and injectors, where clearances between parts are very small and pressures may be rather high. Sulfur in petroleum diesel provides improved lubricity, but contributes to environmental problems.

For petroleum diesel fuels No. 1 and No. 2, the lubricity diameters are 670 and 450 microns, respectively. Adding 1% to 2% by volume of biodiesel to petroleum diesel significantly improves the lubricity of diesel fuel. However, increasing the biodiesel blend beyond 2% has very little impact on the diesel fuel lubricity improvement. The fuel produced reduces the need for sulfur to obtain the desired lubricity characteristics.

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

Fuel Clouding

During cold weather, fuel clouding or wax separation may occur, especially with higher blends of biodiesel. This is referred to as the cloud point. This may lead to fuel filter clogging and hard starting. This should not be a problem with blends of 5% biodiesel, but is a concern at higher levels. One manufacturer recommends the cloud point should be 10°F below the coldest temperature. The pour point is the temperature where the fuel is no longer pumpable, resulting in no fuel being delivered to the engine, leaving it inoperable.

If 100% 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 10°F above the cloud 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 appear to be some additives developed specifically for the biodiesel fuels. 

Cetane Ratings

Cetane rating describes the ignition characteristics of diesel fuel. Using a diesel fuel with a cetane rating lower than the manufacturers’ recommendation can be detected by the diesel knock produced. Fuels with higher ratings will cause an engine to operate more efficiently and will tend to start more easily. Most petroleum fuels on the market have a cetane rating ranging from 40 to 55. The biodiesel fuels have higher ratings, usually in the low to mid 50s.

For older engines, a minimum cetane rating of 40 is frequently recommended. For newer ones, 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 any problems.

Other issues regarding biodiesel fuels include moisture absorption and some seal and material compatibility. All of these issues become more important when using higher blends of biodiesel. Nonetheless, at the 5% level, several normal recommended practices should be used. 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 ensuring the fuel caps are properly installed and more frequently draining water from the water trap on the fuel storage tank to separate the water from the fuel as it is drawn from the storage tank.

When changing from diesel to biodiesel, more contaminants will be present in the fuel initially because the biodiesel acts as a solvent. In the fuel tanks, the biodiesel will break down some of the contaminants adhering to the inside wall of the tank. 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. One manufacturer recommends changing at one-half the normal intervals for the first seven filter changes.

The energy available in each pound of biodiesel fuel is 8% to 10% less than petroleum diesel. For canola- and soybean-derived biodiesel, lower heating value is about 17,900 to 17,400 British thermal units (BTUs) per pound. For petroleum diesel, it is 19,300 BTUs per pound. The density of biodiesel is about 4% to 5% greater than the petroleum diesel.

Under normal engine loads and at 20% or less for biodiesel blend, the operator will not likely perceive a difference in engine performance when switching to biodiesel.

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