ASTM: What It Means and How to Attain ItASTM International (ASTM), originally known as the American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services.
ASTM D6751 Is the name given to the entire suite of tests performed on biodiesel fuel. For a batch of biodiesel fuel to meets or exceed ASTM D6571, it must, by definition, meet or exceed the various specifications that comprise D6751. The following paper discusses some of the most important specifications that are incorporated within the ASTM D6751 suite of tests and describes how the BioPro™ line of processors successful meets them. |
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ASTM D6584: Free & Total Glycerin
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Description of test Free and total glycerin levels within the finished biodiesel are tested under the D6584 specification and are important to biodiesel producers. Free glycerin is an indicator of improperly washed fuel. If the amount of free glycerin exceeds the ASTM specified limit of 0.020% by mass, then it is likely to separate or solidify over time. This is very likely to result in excessive deposits left on valves and engine components as well as clogging and fouling in fuel pumps and lines. |
Why the BioPro passes this test: Because the BioPro line of biodiesel processors employs a three stage washing system with two stages that include vigorous agitation, it has been designed to pass the Free Glycerin test. In fact, we have never seen a fuel sample that was washed in a BioPro that has failed the test for free glycerin. The primary reaction that occurs to transform oils and fats into biodiesel is called a transesterification reaction. The Total Glycerin test indicates how complete the transesterification reaction has been. Fuel that does not meet the specified ASTM maximum value of 0.24% for total glycerin is not as likely to damage an engine as fuel that has excessive free glycerin, however there are negative effects to a high total glycerin number. A high level of total glycerin can lead to cold flow problems as well as a higher viscosity fuel, which can inhibit the spray pattern of a vehicle’s injectors and contribute to carbon buildup and inconsistent starting in cold weather. Fortunately, the BioPro runs a two-stage duel catalyst series of reactions with the capacity to perform an 80/20 reaction as well. The BioPro processors precisely monitor reaction temperature as well as employ a powerful motor dedicated solely to agitating the feedstock during the reaction process. If the user follows the straightforward directions given in the owner’s manual, he will successfully pass D6584. Numerous tests both in-house and by customers in the field have proven the BioPro consistent ability to meet or beat the total glycerin spec. |
EN 14538: Potassium and Sodium by Spectrometric Analysis
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Description of test Technique for detecting and measuring metallic elements in fuel. Along with other metallic elements in the fuel, sodium and potassium can cause hard deposits on the piston crowns, valves and injectors. They can also cause filter clogging and abrasion to engine components. The primary source of potassium and sodium in the fuel is soap formed during the reaction that is not properly removed during the washing stages. |
Why the BioPro passes this test: The 3-stage wash cycle performed by the BioPro™ 190 is the most thorough water washing system on the market. A key factor to its efficiency is the turbulent wash stages in which the water is blended to the point of homogeneity with the fuel. This maximizes the fluid interface and ensures that all wash-related aspects of the ASTM D6751 spec. are met or exceeded. Once again, numerous tests performed by Springboard Biodiesel, LLC. and BioPro™ customers have repeatedly proven the reliability of the BioPro™ washing system. |
ASTM D2500: Cloud and Pour Point
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Description of test The cloud point represents the lowest temperature at which crystals begin to form in the fuel. The pour point is the temperature at which the fuel ceases to flow due to cold temperature solidification. While there is no temperature specification given on ASTM D2500, it is stated that these temperatures should be known. This prevents blenders from using fuel in an application where it is likely to cloud or solidify due to a cold environment. Somewhere in between the cloud and pour point of a specific fuel is the Cold Filter Plugging Point. This is the temperature at which enough of the fuel is solidified that it will plug a fuel filter and cause a dramatic loss of power in a vehicle. While this does not result in any damage to the vehicle, it is a severe inconvenience. Cloud and pour point of a fuel is most closely tied with the characteristics of the fats and oils that the fuel is made from. As a general rule, biodiesel will gel at a temperature of about 30F colder than the feedstock that it was made from. Think of canola oil gelling in your refrigerator at around 40F. If this canola oil was made into biodiesel, it would likely have a gel point in the low teens. |
Why the BioPro passes this test: There is a factor in the cloud point of biodiesel that is not entirely feedstock dependent. If the reaction that transformed the feedstock into biodiesel progressed to a low level of completion, then there will remain in the biodiesel a fairly high level of un-reacted triglycerides. In addition to causing the fuel to fail the bound glycerin test (D6584) the cloud point will be reduced due to the fact that the remaining triglycerides will solidify at a much warmer temperature than the rest of the fuel. As was mentioned above, the BioPro™ series of biodiesel processors have outstanding reaction capabilities to ensure that the best possible reaction is achieved. This will in turn result in the lowest possible cloud point for a given feedstock. |
ASTM D445: Viscosity
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Description of test Viscosity is the measurement of resistance of a fluid to flow. To ensure that adequate supply of fuel reaches the injectors and that there is a proper spray pattern of fuel from the injectors, the viscosity of the fuel must fall within a given range. The test limits for acceptable fuel viscosity are set at 1.9-6.0 cst. If a sample of fuel is poorly reacted (having a large percentage of triglycerides) it is likely to have a viscosity greater than 6.0 cst. At this high viscosity, a poor spray pattern and resulting incomplete fuel combustion is likely to occur. |
Why the BioPro passes this test: Once again, the exceptional ability of the BioPro™s to perform consistently complete and thorough reactions ensures that the resulting fuel will be well within the ASTM viscosity specification. |
ASTM D664: Total Acid Number (TAN)
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Description of test The ASTM D664 test determines how acidic a particular sample of fuel is. It is entirely acceptable for fuel samples to be slightly acidic. The limit set for fuel acidity is 0.5 mgKOH/gram. This means that it takes 0.5 milligrams of Potassium Hydroxide to neutralize the acids in one gram of biodiesel.. The TAN is an indicator of aged fuel that is likely to develop insoluble organic compounds that could present a risk of polymerization and clogging of fuel lines. It also signals acidic fuel that may have solvent properties that are more aggressive than properly processed biodiesel. This fuel poses a risk to various seals, lines, and elastomers in the fuel delivery system. There are two common reasons that a sample of fuel maybe too acidic.
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Why the BioPro passes this test: Because the BioPro™ processor performs a wash with fresh or only slightly acidic water, meeting this specification has never been a problem that typical BioPro™ customers have had to deal with. Typical test results have come in at only a fraction of the required specification. BioPro™ customers that have purchased a SpringPro™ T76 Drywash system will find that they are superbly equipped to meet TAN. Not only does the 2 stage reaction process of the BioPro™ processors result in a lower than usual initial soap level in the raw fuel, but the SpringPro T76 Drywash system itself is specifically designed to minimize TAN. It does this through the use of a duel tower lead/lag setup, which is tailored for the use of an absorbent media in the lead column to remove bulk soaps and an ion exchange resin in the lag column to polish out residual contaminants. This setup and configuration has proven effective for easily meeting the TAN where other systems cannot. |
ASTM D63: Flash Point
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Description of test The flash point is the lowest temperature at which the vapor of a combustible liquid can be made to ignite momentarily in air. The flash point of a fuel relates directly to the ignitability of the fuel. A low flash point can indicate residual methanol remaining from the conversion process. A high flash point can mean the reaction has not proceeded to completion. In a diesel engine, a low flashpoint can cause premature ignition, irregular timing, excessive fuel blow by into the crankcase oil, and excessive emissions. A high flash point can lead to poor ignition, resulting in inconsistent firing, and variable engine performance. It can also indicate potential clogging of fuel lines, filters and injector clogging in cold climates. |
Why the BioPro passes this test: A low flashpoint is almost invariably caused by excessive methanol in the fuel. The thorough wash of the BioPro™ 190 is extremely effective at removing this excess methanol (see the section entitled EN14538). A high flashpoint (although rarely encountered as a problem in the industry) is indicative of a poor reaction. Please see the section entitled ASTM D6584 for more information on the exceptional BioPro™ reaction sequence. Flash point has never been a problem in any of the tests done on finished fuel made in a BioPro processor. |
STM D2709: Water and Sediment
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Description of test Though water is always present in fuel, it is important to control its content. A gross contamination can be detected by a cloudy appearance. Excessive water may indicate a water wash/removal process is not performed correctly. |
Why the BioPro passes this test: Tests run on fuel made in BioPro™ processors typically turn out at only a small fraction of the allowable water content. This is due to the unique evaporation system in the BioPro™. Many small-scale producers of biodiesel rely on extended settling or circulation to attempt to remove trace water. The unparalleled evaporation system of the BioPro™ utilizes a 1/3 hp stir motor and prop to vigorously agitate the fuel while a 250cfm fan blows air over the surface of the fuel creating ideal conditions for rapid and thorough evaporation. |
ASTM D1160: Distillation, 90% Recovery
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Description of test D1160 employs a method of determining the full range of volatility characteristics of a hydrocarbon-based liquid by progressively boiling off a sample under controlled heating. Biodiesel is fundamentally different than petroleum-based diesel, and this is particularly evident with distillation. Biodiesel has a fairly homogeneous consistency of straight chain hydrocarbons, all with 16 to 18 carbons. Consequently it exhibits a boiling point rather than a distillation curve. A high distillation value may indicate the conversion reaction has not gone to completion, Low values indicate methanol carryover. High values lead to poor starting, especially in cold weather; low values can lead to poor timing and seal material failure. |
Why the BioPro passes this test: To understand why the BioPro™ consistently passes this test please note that it is dependent on reaction and washing rigor and see sections entitled ASTM D6584 and EN 14538. |
EN 14112: Oxidative Stability
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Description of test This test measures the propensity of a fuel to oxidize over time. As a fuel oxidizes it tends to form insoluble compounds that may clog filters and injectors. In addition to this, it has a greater likelihood of polymerizing under the high temperatures and pressures of an injection system. This results in a “varnish” buildup on the surfaces of engine parts exposed to the fuel. While to a large extent, oxidative stability is a function of feedstock (typically, the more saturated the fat or oil, the greater the oxidative stability) fuel production procedures have an effect as well. Residual catalyst and other dissolved metals, can catalyze the oxidation of the fuel. |
Why the BioPro passes this test: The thorough wash of the BioPro™ processor (see EN14538) as well as the chemical resistant and stainless steel construction of all of the BioPro™ components minimize this contamination. This is especially true in the case of brass and copper which are widely known as destabilizing agents for biodiesel. The designers of the BioPro™ took great care and expense to make sure that no wetted parts on the machine were made of these metals. |
Sample Test Results
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To the right is a test result received by a random customer who sent in a sample of his fuel made from waste kitchen grease to a testing laboratory. |
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