Biodiesel Test Glossary

Test descriptions are taken from:

• ASTM D 6751-07a
• BQ-9000

Select from Glossary links below:

A–C | D–G | H–K | L–P | Q–T | U–Z

Acid Number (ASTM D664)

The acid number is used to determine the level of free fatty acids or processing acids that may be present in biodiesel. Biodiesel with a high acid number has been shown to increase fueling system deposits and may increase the likelihood for corrosion.

Acid number measures a different phenomenon for biodiesel than petroleum based diesel fuel. The acid number for biodiesel measures free fatty acids or degradation by-products not found in petroleum based diesel fuel. Increased recycle temperatures in new fuel system designs may accelerate fuel degradation which could result in high acid values and increased filter plugging potential.

Ash (ASTM D482)

Ash-forming materials may be present in diesel fuels in two forms: (1) abrasive solids and (2) soluble metallic soaps. Abrasive solids contribute to injector, fuel pump, piston and ring wear, and also to engine deposits. Soluble metallic soaps have little effect on wear but can contribute to engine deposits.

Calcium and Magnesium Combined (EN 14538)

Calcium and magnesium may be present in biodiesel as abrasive solids or soluble metallic soaps. Abrasive solids can contribute to injector, fuel Pump, piston, and ring wear, as well as to engine deposits. Soluble metallic soaps have little effect on wear, but they may contribute to filter plugging and engine deposits. High levels of calcium and magnesium compounds may also be collected in exhaust particulate removal devices, are not typically removed during passive or active regeneration, and can create increased back pressure and reduced time to service maintenance.

Carbon Residue (ASTM D4530)

Carbon residue gives a measure of the carbon depositing tendencies of a fuel oil. While not directly correlating with engine deposits, this property is considered an approximation. Although biodiesel is in the distillate boiling range, most biodiesels boil at approximately the same temperature and it is difficult to leave a 10% residual upon distillation. Thus, a 100% sample is used to replace the 10% residual sample, with the calculation executed as if it were the 10% residual. Parameter E (final weight flask charge/original weight flask charge) of Test Method D 4530-93 is a constant 20/200.

Cetane Number (ASTM D613)

Cetane number is a measure of the ignition quality of the fuel and influences white smoke and combustion roughness. The cetane number requirements depend on engine design, size, nature of speed and load variations, and on starting and atmospheric conditions. The calculated cetane index, Test Methods D 976 or D 4737, may not be used to approximate the cetane number with biodiesel or its blends. There is no substantiating data to support the calculation of cetane index with biodiesel or biodiesel blends.

Cloud Point (ASTM D2500)

Cloud point is of importance that it defines the temperature at which a cloud or haze of crystals appears in the fuel under prescribed test conditions which generally relates to the temperature at which crystals begin to precipitate from the fuel in use. Biodiesel generally has a higher cloud point than the petroleum based diesel fuel. The cloud point of biodiesel and its impact on the cold flow properties of the resulting blend should be monitored by the user to ensure trouble-free operation in cold climates.

Copper Strip Corrosion (ASTM D130)

This test serves as a measure of possible difficulties with copper and brass or bronze parts of the fuel system. The presence of acids or sulfur-containing compounds can tarnish the copper strip, thus indicating the possibility for corrosion.

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Distillation Temperature (ASTM D86 or ASTM D1160)

Biodiesel exhibits a boiling point rather than a distillation curve. The fatty acids chains in the raw oils and fats from which biodiesel is produced are mainly comprised of straight chain hydrocarbons with 16 to 18 carbons that have similar boiling temperatures. The atmospheric boiling point of biodiesel generally ranges from 330 to 357°C thus the specification value of 360°C is not problematic. This specification was incorporated as an added precaution to ensure the fuel has not been adulterated with high boiling contaminants.

Electrical Conductivity at delivery to purchaser (ASTM D2624)

The ability of a fuel to dissipate electric charge that has been generated during pumping and filtering operations is controlled by its conductivity. If a fuel's conductivity is sufficiently high, the static electric charge dissipates fast enough to prevent its accumulation and dangerously high electrical potentials are avoided.

Flash Point (ASTM D93)

The flash point, as specified, is not directly related to engine performance. It is, however, of importance in connection with legal requirements and safety precautions involved in fuel handling and storage that are normally specified to meet insurance and fire regulations. The flash point for biodiesel has been set at 93°C (200°F) minimum, so biodiesel falls under the non-hazardous category under National Fie Protection Association codes.

Free Glycerin & Total Glycerin (ASTM D6584)

The free glycerin method is used to determine the level of glycerin in the fuel. High levels of free glycerin can cause injector deposits, as well as clogged fueling systems, and result in a buildup of free glycerin in the bottom of storage and fueling systems

The total glycerin method is used to determine the level of glycerin in the fuel and includes the free glycerin and the glycerin portion of any unreacted or partially reacted oil or fat. Low levels of total glycerin ensure that high conversion of the oil or fat into its mono-alkyl esters has taken place. High levels of mono-, di-, and triglycerides can cause injector deposits and may adversely affect cold weather operation and fuel filter plugging.

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Kinematic Viscosity (ASTM D445)

For some engines it may be advantageous to specify a minimum viscosity because of power loss due to injection pump and injector leakage. Maximum allowable viscosity, on the other hand, is limited by considerations involved in engine design and size, and the characteristics of the injection system. The upper limit for the viscosity of biodiesel (6.0 at mmˆ2/s at 40 degrees Celsius is higher than the maximum allowable viscosity in specification D 975 Grade 2-D and 2-D low sulfur (4.1 mm/s at 40 degrees Celsius) Blending biodiesel with diesel fuel close to its upper limit could result in a biodiesel blend with viscosity above the upper limits contained in Specification D 975.

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Low Temperature Flow (ASTM D4539)

The low temperature flow test was developed in order to predict low-temperature operability of fuels to which a wax modifier has been added to improve said quality. The low-temperature operability of low-level biodiesel fuels blends can be a limiting factor in some applications. That is, biodiesel ester components typically have relatively high cloud points (–15 to 10 degrees Celsius reported for different biodiesel methyl esters.) Thus, the addition of up to 5% biodiesel ester to a diesel fuel can degrade the low-temperature operability of the low-level biodiesel fuel blend.

Lubricity (ASTM D6079)

A lubricity additive shall be incorporated in the base fuel when the operability temperature is –20 degrees Celsius or lower. This requirement is based upon a correlation between the operability temperature and lab bench test results (using the high frequency reciprocating rig test).

For some engines, diesel fuel is a lubricant for the injection system; therefore it must have sufficient lubricity to ensure fuel system durability and hence emission durability requirements. Diesel fuel lubricity can be defined as the ability of a fuel to prevent or minimize wear in diesel fuel injection equipment.

Oxidation Stability (ASTM EN14112)

Products of oxidation in biodiesel can take the form of various acids or polymers, which, if in high enough concentration, can cause fuel system deposits and lead to filter clogging and fuel system malfunctions. Additives designed to retard the formation of acids and polymers can significantly improve the oxidation stability performance of biodiesel.

Phosphorus Content (ASTM D4951)

Phosphorus can damage catalytic converters used in emissions control systems and its level must be kept low. Catalytic converters are becoming more common on diesel-powered equipment as emissions standards are tightened, so low phosphorus levels will be of increasing importance. Biodiesel produced from U.S. sources has been shown to have low phosphorus content (below 1 ppm) and the specification value of 10 ppm maximum is not problematic. Biodiesel from other sources may or may not contain higher levels of phosphorus and this specification was added to ensure that all biodiesel, regardless of the source, has low phosphorus content.

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Relative Gravity (ASTM D1298)

Relative Gravity testing is required to determine biodiesel production lot and storage tank homogeneity before other testing is carried-out. The need to test for homogeneity is based upon the type of storage tank used, as follows:

• Non Mechanically Mixed or Agitated Tanks

  For each production lot, testing shall be performed to insure the product in the tank is homogeneous.
  Tank homogeneity is established by obtaining tank samples at the upper, middle and lower regions of the tank. All three samples must conform to the Tank Homogeneity requirements. If homogeneity requirements are met then the upper, middle and lower samples can be combined to form a composite sample for testing purposes.

• Mechanically Mixed or Agitated Tanks

  In cases where mechanical tank mixing methods are used, tank homogeneity is established after 5 consecutive production lots meet the Tank Homogeneity requirements. Once established, the producer shall identify the method with which production lot samples will be acquired for testing. If homogeneity cannot be established, then a composite or all levels sample shall be used

Sodium and Potassium Combined (EN 14538)

Sodium and potassium may be present in biodiesel as abrasive solids or soluble metallic soaps. Abrasive solids can contribute to injector, Fuel pump, piston and ring wear, and also to engine deposits. Soluble metallic soaps have little effect on wear, but they may contribute to filter plugging and engine deposits. High levels of sodium or potassium compounds may also be collected in exhaust particulate removal devices are not typically removed during passive or active regeneration, and they can create increased back pressure and reduced period to service maintenance.

Sulfated Ash (ASTM D874)

Ash-forming materials may be present in diesel fuels in two forms: (1) abrasive solids and (2) soluble metallic soaps, and (3) un-removed catalysts. Abrasive solids and un-removed catalysts contribute to injector, fuel pump, piston and ring wear, and also to engine deposits. Soluble metallic soaps have little effect on wear but can contribute to filter plugging and engine deposits.

Sulfur (ASTM D5453)

The effect of sulfur content on engine wear and deposits appears to vary considerably in importance and depends largely on operating conditions. Fuel sulfur can also affect emissions control systems performance and various limits on sulfur have been imposed for environmental reasons. B100 is essentially sulfur-free.

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Visual Appearance Inspection (procedure 2) (ASTM D4176)

Visual inspection indicates successful biodiesel reaction in 2 distinct layers. Top layer: 80–90% product, lighter colour than the bottom layer, it is biodiesel Bottom Layer: 10–20% of the reaction, darker colour, a mixture of glycerin, catalyst/lye, alcohol & possibly food particles A milky middle layer in the test batch indicates a production of soap (due to water in vegetable oil or too much lye). Biodiesel with this middle layer should undergo a water wash. Unsuccessful reactions result in no layering or one solid batch of soap.

Water in Oil (ASTM D6304)

Moisture is considered a chemical contaminant when suspended or mixed with lubricating oils. It presents a combination of chemical and physical problems for the lubricant and machinery, respectively. The effects of water are insidious. Failure due to water contamination may be catastrophic, but it may not be immediate. Many failures blamed on lubricants are truly caused by excess water. The following are some of the effects of water on equipment:

• shorter component life due to rust and corrosion;
• water etching/erosion and vaporous cavitations;
• hydrogen embrittlement;
• oxidation of bearing Babbitt;
• wear caused by loss of oil film or hard water deposits;

Water & Sediment (ASTM D2709)

Testing shall be conducted in accordance with ASTM D 1796 (modified) or D2709. The test in ASTM D 1796 shall be modified by substituting the centrifuge tube specified in ASTM D 2273 for that in ASTM D 1796. In the event of a dispute, ASTM D 1796 (modified) shall be the referee test.