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Biodiesel Frequently Asked Questions

Questions & Answers

Q: What is Biodiesel?
A: Biodiesel is a clean burning alternative fuel, produced from domestic, renewable resources. Pure biodiesel (B100) contains no petroleum, but it can be blended at any level with petroleum diesel to create a biodiesel blend. Blends typically range from B5 (5% biodiesel and 95% petroleum diesel fuel) to B20 (20% biodiesel and 80% petroleum diesel fuel). It can be used in compression-ignition (diesel) engines with little or no modifications. Biodiesel is simple to use, biodegradable, nontoxic, and essentially free of sulfur and aromatics.

Q: Why should I use biodiesel?
A: There are several advantages to using biodiesel and biodiesel blends:

  1. It's better for the environment! Biodiesel has a lower toxicity level than petroleum diesel and lower emissions of carbon monoxide, sulfur oxides and particulates.
  2. It's better for your engine! Biodiesel has a greater lubricity and reduces engine wear.
  3. It's renewable! Unlike petroleum, we can produce more biodiesel every year.
  4. It increases national security! Using biodiesel helps reduce U.S. dependence on foreign oil.
  5. It is produced domestically! Biodiesel production stimulates local economies and promotes local agriculture, both of which put money back into the U.S. economy.

Q: How do biodiesel emissions compare to petroleum diesel?
A: Biodiesel is the only alternative fuel to have fully completed the health effects testing requirements of the Clean Air Act. The use of biodiesel in a conventional diesel engine results in substantial reduction of unburned hydrocarbons, carbon monoxide, and particulate matter compared to emissions from diesel fuel. In addition, the exhaust emissions of sulfur oxides and sulfates (major components of acid rain) from biodiesel are essentially eliminated compared to diesel.

Of the major exhaust pollutants, both unburned hydrocarbons and nitrogen oxides are ozone or smog forming precursors. The use of biodiesel results in a substantial reduction of unburned hydrocarbons. Emissions of nitrogen oxides are either slightly reduced or slightly increased depending on the duty cycle of the engine and testing methods used. Based on engine testing, using the most stringent emissions testing protocols required by EPA for certification of fuels or fuel additives in the US, the overall ozone forming potential of the speciated hydrocarbon emissions from biodiesel was nearly 50 percent less than that measured for diesel fuel.

Biodiesel emissions have decreased levels of polycyclic aromatic hydrocarbons (PAH) and nitrited PAH compounds that have been identified as potential cancer causing compounds. Test results indicate PAH compounds were reduced by 75 to 85 percent, with the exception of benzo(a)anthracene, which was reduced by roughly 50 percent.

Q: Can I use biodiesel in my existing diesel engine?
A: Typically biodiesel blends up to 20% (B20) can be operated in any diesel engine with little or no modification to the engine or the fuel system. Biodiesel has a solvent effect that may release deposits accumulated on tank walls and pipes from previous diesel fuel storage. The release of deposits may clog filters initially and precautions should be taken to change them when needed. Ensure that only biodiesel meeting the Tennessee Department of Agricultures' specification is used.

Q: How do I make the switch to biodiesel?
A: If you plan to switch to B100 (100% biodiesel), it is often recommended that you start with B5 (5% biodiesel) and gradually increase the biodiesel concentration over a period of several months. The reasons are two-fold. First, biodiesel has strong solvent properties. It tends to clean fuel tanks and lines of built-up residues, which will then accumulate in the fuel filter. So you may have to change your filters more frequently when first using biodiesel. Second, it allows you to optimize the diesel to biodiesel ratio for your weather conditions. You should be aware that in the coldest months of the year, the biodiesel ratio will probably have to be decreased, unless you add an external heating device to your engine. However, as the temperature rises, so can your biodiesel concentration.

Q: Will I void the manufacturer's warranty if I use biodiesel?
A: Warranties vary significantly from one manufacturer to the other. Most will not categorically void a warranty if you use biodiesel. However, most warranties will not cover damage that was caused by a fuel (be it biodiesel of any other fuel) because those damages were not caused by a defect in the machine. For instance, if you damage a diesel engine by accidentally putting gasoline in the tank, the manufacturer will probably not repair the engine under warranty. Therefore, it may be more difficult to get warranty coverage for problems that may been caused by biodiesel. Furthermore, many manufacturers are reluctant to recommend use of blends higher than B5 in their engines. Check carefully with the individual manufacturer to verify what is covered and/or recommended.

Q: Where can I purchase biodiesel?
A: Biodiesel is available in over 30 refueling stations across Tennessee.

An up to date listing of East Tennessee biodiesel refueling stations can be found at https://www.etcfc.org/refuel.html#biodiesel.

An up to date listing of West Tennessee biodiesel refueling stations can be found at https://cleancities.energy.gov/coalitions/locations/.

Q: Is Biodiesel the same thing as raw vegetable oil?
A: No! Biodiesel can be produced from any fat or vegetable oil (most U.S. biodiesel is made from soy bean oil), through a refinery process called transesterification. All vegetable oils have different properties that make them either a good source for biodiesel or not. Biodiesel can be made from fresh oil or even used cooking oil from restaurants.

The transesterification process is a reaction between the oil and alcohol, which removes the glycerin. Glycerin is a by-product of biodiesel production. Fuel-grade biodiesel must be produced to strict industry specifications (ASTM D6751) in order to insure proper performance. Biodiesel that meets ASTM D6751 and is legally registered with the Environmental Protection Agency is a legal motor fuel for sale and distribution. Raw vegetable oil cannot meet biodiesel fuel specifications, it is not registered with the EPA, and it is not a legal motor fuel.

Q: Is it approved for use in the U.S. and Tennessee?
A: Biodiesel is registered as a fuel and fuel additive with the Environmental Protection Agency (EPA) and meets clean diesel standards established by the California Air Resources Board (CARB). Pure (B100) biodiesel has been designated as an alternative fuel by the Department of Energy (DOE) and the US Department of Transportation (DOT). In most applications, if the biodiesel conforms to the ASTM International D6751 standards it can be used in the same equipment as other diesel fuels. Contact your equipment manufacturer or refer to your owner's manual for biodiesel use guidance for your equipment.

The Tennessee Department of Agriculture is currently testing biodiesel being sold and has developed fuel quality standards that provide a level of quality assurance necessary to protect diesel equipment when blends up to 20 percent are used.

Q: What type of certification process must I go through to produce or sell biodiesel in Tennessee?
A: The Tennessee Department of Agriculture tests all grades of biodiesel produced and sold in Tennessee. Their requirements are as follows:

  1. All Biodiesel blend stock intended for blending with diesel fuel shall meet the most recent version of ASTM D 6751, "Standard Specification for Biodiesel Fuel (B100) Blend Stock for Distillate Fuels."
  2. Blends of biodiesel and diesel fuels shall meet the following requirements: the base diesel fuel shall meet the most current requirements of ASTM D 975, Standard Specification for Diesel Fuel Oils; the biodiesel blend stock shall meet the most current requirements of ASTM D 6751, Standard Specification for Biodiesel Fuel (B100) Blend Stock for Distillate Fuels, with the following exception: Biodiesel may be blended with diesel fuel whose sulfur, lubricity, or aromatic levels are outside specification ASTM D 975, Standard Specification for Diesel Fuel Oils, Grades 1-D, low sulfur 1-D, 2-D, or low sulfur 2-D, provided the finished mixture meets pertinent national and local specifications and requirements for these properties.
  3. Biodiesel blends up to 5% by volume shall meet the most recent version of ASTM D 975, "Standard Specification for Diesel Fuel Oils". At such time that an ASTM standard specification is developed for blends up to 5%, the ASTM standard shall prevail as rule.
  4. Biodiesel blends more than 5% and up to 20% by volume shall meet the most recent version of ASTM D 975, "Standard Specification for Diesel Fuel Oils", except that the maximum temperature of the 90 percent volume recovered distillation point shall be five degrees centigrade greater than that specified in Table 1 of ASTM D 975. At such time that an ASTM standard specification is developed for blends greater than 5% and up to 20%, the ASTM standard shall prevail as rule.
  5. All biodiesel blends must meet the tenth percentile minimum ambient temperature values for low temperature operability as published in ASTM D 975 Appendix X.4. Low temperature operability may be qualified by either ASTM Standard Test Method D 4539 or ASTM Standard Test Method D 2500.
  6. Biodiesel conveyed at retail sale points that are available to the general consuming public shall not exceed 20% by volume.

The Department of Agriculture urges all potential blenders to request the biodiesel blend stock supplier to provide documentation that a representative sample of the material being produced has been inspected and tested by the Tennessee Department of Agriculture. If there are any questions regarding the inspection and test results, contact the Department of Agriculture for assistance in determining if the blend stock has been tested and approved. To discuss fuel quality issues, the Department of Agriculture may be contacted at 1-800-OCTANE1 (1-800-628-2631).

Q: How much biodiesel has been sold in the US?
A: Sales of biodiesel have dramatically increased in less than one million gallons in 1999 to approximately 75 million gallons in 2005. The National Biodiesel Board has released the following sales volume estimates for the US:

Quantity of Biodiesel Sold in the U.S.