Vegetable Oil Blended Diesel Fuel

Vegetable Oil Blended Diesel Fuel, or Biofuels Blended Diesel (BBD), or Waste Oil Blended Diesel Fuel (WOBDF) is the process of making a diesel fuel out of a blend of oils and solvents. The purpose of making a Vegetable Oil Blended Diesel Fuel is to thin the resulting blended fuel to near the viscosity of diesel fuel, to improve the blend’s burn characteristics, and reduce its gel-point. The resulting solution should be a uniform solution without precipitates.
History
Rudolf Diesel was the inventor of the engine that bears his name. His first attempts were to design an engine to run on coal dust, but a few years later redesigned his engine to run on vegetable oil. The idea, he hoped, would make his engines more attractive to farmers having a source of fuel readily available from their agricultural products. In a 1912 presentation to the British Institute of Mechanical Engineers, he cited a number of efforts in this area and remarked, "The fact that fat oils from vegetable sources can be used may seem insignificant today, but such oils may perhaps become in course of time of the same importance as some natural mineral oils and the tar products are now."
Periodic petroleum shortages spurred research into alternative fuels, such as vegetable oil as a diesel substitute during the 1930s and 1940s, and again in the 1970s and early 1980s when straight vegetable oil enjoyed its highest level of scientific interest. The 1970s also saw the formation of the first commercial enterprise to allow consumers to run straight vegetable oil in their automobiles, Elsbett of Germany. In the 1990s Bougainville conflict, islanders cut off from oil supplies due to a blockade used coconut oil to fuel their vehicles.
Academic research into vegetable oil-based fuels fell off sharply in the 1980s with falling petroleum prices and greater interest in biodiesel as an option that did not require extensive vehicle modification. With the rise of petroleum prices after 2000 renewed interest in vegetable oil-based fuels has increased. And, with greater use of biodiesel consumers and producers of biodiesel have found that it tends to gel in cold weather. Amateurs have found by blending various solvents with biodiesel they can keep it liquid at low temperatures. Since then some have found that by adding more solvents to an oil the oil can be made to burn efficiently in a diesel engine not requiring the chemical process for making biodiesel, and will remain liquid at temperatures as low as -30F (-34c).
Low Temperature Gelling
There are other factors in choosing a solvent for blending. The most common other factor is the gel-point of the resulting solution. The gel-point of oils and solvents is the point at which a substance begins to solidify. When biodiesel is cooled below a certain point, some of the molecules aggregate and form crystals. As biodiesel is cooled further it will gel and then solidify plugging the fuel filter. There are a number of commercially available additives that will significantly lower the pour point and cold filter plugging point of pure biodiesel. Winter operation is also possible by blending biodiesel with other fuel oils including #2 low sulfur diesel fuel and #1 diesel / kerosene or even gasoline (petrol).
Gel-point of Blended Biofuels Diesel
Vegetable oils tend to gel at about 32F (0c).
Diesel fuel gels at about -22F (-30c).
Kerosene (paraffin) gels at about -60F (-51c).
And, gasoline (petrol) gels at about -131F (-90c).
However, a blend gels at a point between the gel points of its components, and is a function of the volumetric relationship between those components.
Cosolvent blending
“Vegetable oils are an attractive renewable source for alternative diesel fuels. However, the relatively high kinematic viscosity of vegetable oils must be reduced to make them more compatible with conventional compression-ignition engines and fuel systems. Cosolvent blending is a low-cost and easy-to-adapt technology that reduces viscosity (and gell point) by diluting the vegetable oil with a low-(molecular weight solvent).”
The common method of Blending Biofuels Diesel
The most common method of blending is to blend a petroleum distillate with a vegetable oil to thin it out to near the viscosity of diesel fuel. The most common petroleum distillates used in blending are gasoline (petrol), kerosene (paraffin) and/or diesel fuel. Note: kerosene (paraffin) is not a street-legal fuel in some nations, so there might be heavy fines resulting in their use.
Other commonly used solvents
Other solvents successfully used in making blended biofuels for diesel engines are: Acetone, Methyl Ethel Ketone (MEK), Pure Gum Turpentine (PGT), Xylene, Toluene, lacquer thinner, citrus oils, mineral spirits, paint thinner. Note: some of these solvents are not street-legal, so there might be heavy fines resulting in their use. They may also be hard on hoses and seals.
Theory behind Blending Biofuels Diesel
A solvent is used to reduce the viscosity of the source oil, because the viscosity of vegetable oils varies from plant oil to plant oil; however, the average is about 12 times as viscous as diesel fuel. Viscosity is also a function of temperature, thus blend ratio is also a function of operating temperature.
Commonly used solvents in Blending Biofuels Diesel
Since the viscosity of diesel fuel is twice that of gasoline (petrol), then one needs to use twice as much diesel fuel as gasoline (petrol) for the same thinning effect. And, the viscosity of kerosene (paraffin) is halfway between that of diesel fuel and gasoline (petrol), so half again as much kerosene (paraffin) is needed as gasoline (petrol) to produce a functional vegetable oil-based road fuel for diesel engines.
The typical functional blend ratios and useful temperature ranges
50% diesel fuel to 50% vegetable oil will run fine in a heated fuel line up to 212F (100c), and down to 28F (-2c) operating temperature.
30% kerosene (paraffin) to 70% vegetable oil will run fine in a heated fuel line up to 212F (100c), and down to 15F (-10c)operating temperature.
20% gasoline (petrol) to 80% vegetable oil will run fine in a heated fuel line up to 120F (50c) and down to 0F (-18c)operating temperature.
Blends of more than one solvent can be used
Some people prefer blending diesel fuel, vegetable oil and gasoline (petrol). Here are some functional relationships between the three components:
5% gasoline (petrol), to 40% diesel fuel, to 55% vegetable oil.
10% gasoline (petrol), to 30% diesel fuel, to 60% vegetable oil.
15% gasoline (petrol), to 20% diesel fuel, to 65% vegetable oil.
20% gasoline (petrol), to 10% diesel fuel, to 70% vegetable oil.
25% gasoline (petrol), to 0% diesel fuel, to 75% vegetable oil.
Blends with biodiesel
It is also common practice to blend solvents into biodiesel to prevent it from gelling at cold temperatures.
Gasoline (petrol), to Biodiesel blend ratios:
5% gasoline (petrol), to 95% biodiesel 28F (-2c) operating temperature.
10% gasoline (petrol), to 90% biodiesel 20F (-7c) operating temperature.
15% gasoline (petrol), to 85% biodiesel 10F (-12c) operating temperature.
20% gasoline (petrol), to 80% biodiesel 0F (-18c) operating temperature.
25% gasoline (petrol), to 75% biodiesel -10F (-23c) operating temperature.
Note: not all biodiesel gels at the same temperature, so biodiesel made from high melting point esters (HMPE) amy require higher levels of gasoline (petrol) added to it to prevent gelling.
The Blending Method
Blending methods vary; however, the most common method of making Blended Biofuels Diesel (BBD) is to blend the solvent with the source vegetable oil prior to settling, de-watering and filtering, because blending solvents with vegetable oils has three basic functions. Blending reduces the viscosity of the source oil, reduces its gel-point, and tends to force water, and other contaminants, out of solution. This means that thinned oil will drop its contaminant load much more quickly than the more viscous source oil. Where it is common for Straight Vegetable Oil users will settle their oil for weeks, blenders find they can settle their blend for as little as a few hours to a few days.
Thinned vegetable oils will also pass through a filter more quickly than the more viscous source oil. Where Straight Vegetable Oil users may gravity feed their SVO through a filter taking days, thinned vegetable oils will pass through a filter in minutes.
Blended oils will also remain liquid at lower temperatures, so that filtering can take place at much colder temperatures than the source oil will allow.
A solvent that is readily soluble in vegetable oils, such as petroleum distillates, do not require a great deal of agitation to dissolve into the source vegetable oil, and will remain in solution indefinitely. Thus, most blenders fill a settling drum to about 75% full with the source oil, then pour on top of that oil their solvent, such as gasoline (petrol), then rock the drum a little, or swirl a paddle a few times around in the solution.
Settling
Settling Blended Biofuels Diesel (BBD) prior to filtering is simply allowing the blend to remain undisturbed in its settling drum for anywhere from 3 hours to 3 days.
After an adequate settling period most blenders will drain off the precipitates that settle to the bottom of the settling drum. To facilitate drain off the precipitates blenders will tend to have a cone-shaped, or bell-shaped bottom on their settling drum, and will have a valve at the bottom for draining off those precipitates.
Precipitates
The precipitates that settle out from a blend will begin to settle out within minutes after agitation ceases. Those precipitates are primarily particulates and liquids. The particulates precipitates are mostly particles of dust, free-carbon and food particles. The liquid precipitate is mostly water, but there can also be animal fat and lacquers. The water precipitate can contain dissolved components which are common in the commercial kitchen, such as: salt, sugar and spices. Animal fat is problematic because of its high melting point. Lacquer is naturally occurring in vegetable oils.
Filters and Filtering
Cartridge and bag filters that are deigned for filtering drinking water are commonly used for filtering Blended Biofuels Diesel (BBD). They are very effective for filtering these fuel blend; however, one must keep in mind that some nations blend alcohol at various percentages into gasoline (petrol) fuel stocks. The alcohol content in gasoline (petrol) can cause deterioration of fuel hoses, seals and filter seals, so if one blends with gasoline (petrol), then one should be aware of the alcohol content in this fuel. Or, filter with bag filters which are not affected by alcohol content in the fluid stream being filtered.

Main Menu

See Also

Main Menu