BIODIESEL QUALITY SPECIFICATIONS

The American Society for Testing and Materials International (ASTM) specification for biodiesel (B100) is ASTM D6751-07a. is summarized in the Specification Table below. This specification is intended to insure the quality of biodiesel to be used as a blend stock at 20% and lower blend levels. Any biodiesel used in the United States for blending should meet ASTM D6751 prior to blending. ASTM is a consensus based standards group comprised of engine and fuel injection equipment companies, fuel producers, and fuel users whose standards are recognized in the United States by EPA and most government entities including states with the responsibility of insuring fuel quality.

As with other ASTM fuel standards, ASTM D6751 is based on the physical and chemical properties needed for safe and satisfactory diesel engine operation. It is not based on the specific raw materials or the manufacturing process used to produce the biodiesel. The finished blend stock must meet the properties specified below as well as the following definition:

Biodiesel, [noun]: a fuel comprised of mono-alkyl esters of long chain fatty acids
derived from vegetable oils or animal fats, designated B100.

SPECIFICATION FOR BIODIESEL (B100) -ASTM D6751-07a

March 2007

Biodiesel is defined as the mono alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, for use in compression-ignition (diesel) engines. This specification is for pure (100%) biodiesel prior to use or blending with diesel fuel.

BOLD = BQ-9000 Critical Specification Testing Once Production Process Under Control
The carbon residue shall be run on the 100% sample.

A considerable amount of experience exists in the US with a 20% blend of biodiesel with 80% diesel fuel (B20). Although biodiesel (B100) can be used, blends of over 20% biodiesel with diesel fuel should be evaluated on a case-by-case basis until further experience is available.

The definition of biodiesel contained in ASTM D 6751, along with the physical and chemical property limits, eliminates certain "biofuels" that have been incorrectly called biodiesel in the past. The raw vegetable oil or animal fat feedstock, partially reacted oils or fats, coal slurries, or any other "biologically derived" fuels not meeting the definition and table above are not biodiesel and should not be confused with biodiesel.

The ASTM biodiesel standard began as a standard for B100 as a standalone motor fuel. During the ASTM ballot process, lack of experience with blends over B20 did not allow ASTM to come to consensus on the properties needed for satisfactory B100 operation. The standard was renamed to reflect its formal approval by ASTM as applying to a blend stock but not to a standalone motor fuel. While D6751 can be used as the standard for B100 as a neat motor fuel upon consultation with the equipment manufacturer, and is being used successfully for that purpose in the United States today, users and suppliers should recognize that D6751 does not have full ASTM consensus as a standalone fuel specification and that B100 is only recognized by a select few equipment manufacturers.

Buyers and sellers are encouraged to use ASTM D6751 for the commercial trading of biodiesel
(B100) whether the fuel is planned for B100 use or for blending. Other arrangements or specifications can legally be used provided both the buyer and seller agree upon them and so long as they meet pertinent local, state, and federal regulations (i.e. EPA sulfur limits, OSHA safety limits on flash point, etc.).

Some of the test methods listed in Specification Table perform more than one role to ensure that the fuel performs as intended in CI engines and as tests to ensure that the manufacturer produced a high-quality B100. The intent of each quality requirement in the Table is described below:

A minimum flash point for diesel fuel is required for fire safety. B100's flash point is typically much higher than diesel fuel's (150° C compared to 70° C) to ensure that the manufacturer has removed excess methanol used in the manufacturing process. Residual methanol in the fuel is a safety issue because even very small amounts reduce the flash point. Residual methanol, which can be found in biodiesel with low, out-of-specification flash point, can also affect fuel pumps, seals, and elastomers, and can result in poor combustion properties.

• Water and sediment refers to the presence of free water droplets and sediment particles. The allowable level for B100 is set at the same level allowed for conventional diesel fuel. Poor drying techniques during manufacturing or contact with excessive water during transport or storage can cause B100 to be out of specification for water content. Excess water can lead to corrosion and provides an environment for microorganisms. Fuel oxidation also can raise sediment levels, so this test can be used in conjunction with acid number and viscosity to determine if fuels have oxidized too much during storage.

• A minimum viscosity is required for some engines because of the potential for power loss caused by injection pump and injector leakage. This is not an issue for B100 and the minimum is set at the same level as for petroleum diesel. The maximum viscosity is limited by the design of engine fuel injection systems. Higher viscosity fuels can cause poor fuel combustion that leads to deposit formation as well as higher in-cylinder penetration of the fuel spray, which can result in elevated engine oil dilution with fuel. The maximum allowable viscosity in ASTM D975 for No. 2 diesel is 4.1 mm2/s at 40°C although most engines are designed to operate on fuels of higher viscosity than 4.1 mm2/s. ASTM D6751 allows for slightly higher viscosity than D975 primarily because that is where the normal viscosity of B100 lies. Consult your operational manual or your engine manufacturer if you intend to use a B100 in your engine that has a higher viscosity than the engine or fuel system was designed to use.

• The sulfated ash test measures the amount of residual alkali catalyst present in the biodiesel as well as any other ash forming compounds that could contribute to injector deposits or fuel system fouling.

• Sulfur is limited to reduce sulfate and sulfuric acid pollutant emissions and to protect exhaust catalyst systems when they are deployed on diesel engines in the future. Biodiesel generally contains less than 15 ppm sulfur. The test for low-sulfur fuel (ASTM D5453) should be used for accurate results instead of D2622, which will provide falsely high results due to test interference with the oxygen in the biodiesel.

• The copper strip corrosion test is used to indicate potential difficulties with copper and bronze fuel system components. The requirements for B100 and conventional diesel are identical, and biodiesel meeting other D6751 specifications always passes this test. While copper and bronze may not corrode in the presence of biodiesel fuel, prolonged contact with these catalysts can cause fuel degradation and sediment formation.

• An adequate cetane number is required for good engine performance. Conventional diesel must have a cetane number of at least 40 in the United States. Higher cetane numbers help ensure good cold start properties and minimize the formation of white smoke. The ASTM limit for B100 cetane number is set at 47 as this is the level identified for "Premium Diesel Fuel" by the National Conference of Weights and Measures, as well as the fact that 47 has been the lowest cetane number found in U.S. biodiesel fuels. The cetane index (ASTM D976) is not an accurate predictor of cetane number for biodiesel or biodiesel blends since it is based on a calculation using specific gravity and distillation curve, both of which are different for biodiesel than for petrodiesel.

• Cloud point is important for ensuring good performance in cold temperatures. B100 cloud point is typically higher than the cloud point of conventional diesel. Low temperature properties and strategies for ensuring good low-temperature performance of biodiesel blends are discussed in more detail in the following chapters.

• Carbon residue gives a measure of the carbon-depositing tendency of a fuel and is an approximation of the tendency for carbon deposits to form in an engine. For conventional diesel fuel the carbon residue is measured on the 10% distillation residue. Because B100 boils entirely in the high end of the diesel fuel range and at approximately the same temperature it is difficult to leave only a 10% residual when distilling biodiesel. So biodiesel carbon residue specifies that the entire biodiesel sample be used rather than the 10% distilled residue.

• Acid number for biodiesel is primarily an indicator of free fatty acids (natural degradation products of fats and oils) and can be elevated if a fuel is not properly manufactured or has undergone oxidative degradation. Acid numbers higher than 0.80 have been associated with fuel system deposits and reduced life of fuel pumps and filters.

• Free and total glycerin numbers measure the amount of unconverted or partially converted fats and byproduct glycerin present in the fuel. Incomplete conversion of the fats and oils into biodiesel can lead to high total glycerin. Incomplete removal of glycerin can lead to high free glycerin and total glycerin. If these numbers are too high, storage tank, fuel system, and engine fouling can occur. Fuels that exceed these limits are highly likely to cause filter plugging and other problems.

• Phosphorus content is limited to 10 ppm maximum in biodiesel because phosphorus can damage catalytic converters and phosphorus above 10 ppm can be present in some vegetable oils. Biodiesel produced in the United States generally has low phosphorus levels, on the order of 1 ppm.

• The T90 distillation specification was incorporated to ensure that fuels have not been contaminated with high boiling materials such as used motor oil. B100 exhibits a. boiling point rather than a distillation curve. The fatty acids from which biodiesel is produced are mainly straight chain hydrocarbons with 16 to 18 carbons that have close boiling temperatures. The atmospheric boiling point of biodiesel generally ranges from 330°C to 357°C.

The D6751 specification also includes the following workmanship statement: "The biodiesel fuel shall be visually free of undissolved water, sediment, and suspended matter." B100 should be clear, although it may come in a variety of colors. Biodiesel color does not predict fuel quality.

Currently there are ASTM specifications for B100 (D6751) and for petrodiesel (D975), but there is not a separate approved specification for biodiesel blends. Current practice to insure the quality of biodiesel blends is to use petrodiesel (No. 1 or No. 2) meeting D975 and biodiesel meeting D6751 prior to blending. Once blended, it is very difficult to determine the quality of the B100 used to make the blend. ASTM specifications for finished biodiesel blends up to B20 are under development, so please check with ASTM or the National Biodiesel Board (NBB) for updated information.

B5 and lower blends generally meet the properties listed in ASTM D975, which defines the properties of conventional diesel fuel. B20 or higher blends can also meet the properties listed in ASTM D975 with the possible exception 'of viscosity and distillation, depending mostly on the diesel fuel with which it is blended. The engine community has generally agreed that a slightly higher distillation with biodiesel blends will not cause the technical problems associated with high boiling petrodiesel fuel-provided the increase is due to biodiesel meeting D6751. They have also stated that a higher viscosity than allowed by D975 may cause added stress on the fuel system and inadequate fuel atomization that can result in poor engine performance and injector coking. Biodiesel blends that meet ASTM D975 can generally be used interchangeably with diesel fuel for normal usage, as long as the biodiesel meets the requirements of ASTM D6751 and the cold flow properties of the blend are adequate for the geography and time of year the fuel will be used.