Biodiesel ASTM Tests (D6751)

Have you ever wondered how good your fuel really is? Do you wonder if it’s good enough to sell? Well, there is a way to find out. It’s called ASTM Testing and it’s the gold standard that is used by the IRS and by the EPA in the United States to determine if Biodiesel really is up to the commercial standard.

To have your fuel ASTM Tested is extremely easy! Several labs across the United States are set up to perform these tests according to the EPA and IRS requirements. To have your fuel tested, you simply send in a specified amount of fuel to the lab you choose, they run a series of tests, and then they typically email, mail, or fax you back the results.

To make it easy for our customers to have their fuel tested, we partnered with a lab out of Vancouver, Washington called Fuel Only. They offer a wide variety of tests and usually have results ready within 72 hours.

There are 15 unique tests that make up the Biodiesel ASTM Standard and most labs will allow you to perform all of these tests at the same time or just a few of them depending on your preference. The tests performed on Biodiesel are laid out in the ASTM D 6751-08 standard. We have summarized each one of these tests below.

ASTM D6584-Total & Free Glycerin Total 0.24% Free 0.02%
This test is by far the most important one. It’s a measurement of how much glycerin is left in the finished product. Too much glycerin indicates the reaction didn’t go well or that the fuel wasn’t properly washed.

ASTM D445-Viscosity @ 40 deg. C Limit 1.9-6.0 cst
This is an indicator of how viscous the Biodiesel is. If it’s too thick it won’t flow right in the fuel system. It’s very rare that Biodiesel ever fails this test. If it does, it’s usually an indication that there’s still a lot of oil in the fuel or some other contaminant.

ASDM D664-Acid Number Limit 0.50 mg KOH/gm
This indicates how acidic the fuel is (similar to what a titration measures, only much more accurate). If fuel is acidic it’s an indication of high free fatty acid levels or other acidic contaminants still present in the fuel. Highly acidic fuel can corrode fuel injection components.

ASTM D1160-Distillation Temperature Limit 360 Deg F Max
This is a test that measures what components “boil off” as a sample is heated. Biodiesel has a known boiling point. If during distillation the sample exceeds that point excessively, it’s a good indication that there may still be oil in the sample. If it all distills off too low, then other contaminants may also be present.

ASTM D613 Cetane Number – 47 Minimum
This test relates to how well the sample will ignite. Biodiesel purposely put this number higher than diesel in the specification to brag about how good Biodiesel is. It’s extremely rare that this test fails, if it does, it means your sample probably isn’t Biodiesel or has high levels of contaminants in it.

ASTM D2500 – Report To Customer – No Limit
This indicates at what temperature a sample of Biodiesel clouds up. It gives an indication of when Biodiesel will begin to gel. Granted, clouding & gelling are two different things, but this test will give you a good ball park figure.

ASTM D93 – Flash Point Limit 93 Deg C Minimum
This test indicates at what point a sample of Biodiesel will ignite in the presence of a flame as the temperature of the sample is raised. If it ignites before 93 Degrees Celcius (approx. 200 Deg. F), it indicates the presence of a highly combustible material in the fuel (usually methanol). This also impacts how the Biodiesel may be shipped. If its flash point is too low, the transport vehicle must be marked as flammable and hazardous. If this test is failed, it usually means you haven’t removed all the methanol from the Biodiesel (ie. The Biodiesel wasn’t properly washed all the way).

ASTM D5453 – Sulfur Content – S15 – <=15PPM, S500 – <=500 PPM
This test is looking for the presence of sulfur in Biodiesel. Onroad Biodiesel can only have 15 parts per million (0.0015%) of sulfur. Biodiesel for off-road use can only have up to 500 parts per million (0.05%). This is a mandate by the EPA. Fail this test and you can’t sell the Biodiesel in the US. This also applies to diesel fuel too. It’s rare for Biodiesel to fail this test unless there are contaminants in the fuel.

ASTM D4951 – Phosphorus <= 0.001% , Sodium & Potassium <=0.005%, Calcium & Magnesium <=0.005%
This one is actually 3 tests combined and is done by spectrochemical analysis. The limits for Calcium & Magnesium combined are a max of 5 ppm, Sodium & Potassium have a max of 5 ppm. Phosphorus is 1 ppm. If you fail this test it’s an indication that the fuel wasn’t properly washed. It’s also a good indication that there’s still soap in the fuel too. I’ve seen some customers fail this simply because the water they were using to wash with had some of these components in it. This is also the test that is extrapolated out to identify the 41 PPM limit of soap in NaOH reacted Biodiesel and 66 PPM limit of soap in KOH reacted Biodiesel when testing fuel for soap content.

ASTM D2709 – Sediment & Water – Max 500 PPM (0.05%)
This indicates the presence of free water and sediment in Biodiesel. The test is performed by spinning a sample of Biodiesel in a centrifuge at high speed. Water obviously will cause problems in fuel systems and sediment can plug filters and leave deposits. There some speculation that this test may be removed in the near future for ASTM D6304, which is Water Testing by Karl Fisher because the Karl Fisher is a more accurate representation of all water in the fuel. If you fail this test, you most likely haven’t dried or filtered your fuel enough.

ASTM D874 – Sulfated Ash – Max of 200 PPM (0.02%)
In this test a sample of fuel is burned and the ash residue is measured. If the ash levels are too high (ie. sulfated ash) then the sample fails. It’s usually an indication that there are contaminants in the fuel since Biodiesel will burn completely.

ASTM D4530 – Carbon Residue – Max 500 PPM (0.05%)
Carbon residue in fuel can lead to carbon deposits in the engine. Too much can cause engine problems down the road.

ASTM D130 – Copper Strip Corrosion Rating – #3 Maximum
This tests the corrosive nature of the Biodiesel sample. If it’s too high, then it can corrode internal engine components. It usually indicates contaminants in the fuel.

EN14112 – Oxidation Stability – 3 Hours Minimum
The fuel is tested to see how quickly it oxidizes. If it oxidizes too quickly this means the fuel can go bad too fast while in storage. Several variables will impact this measure such as the type of oil that’s used, however there are several additives on the market that can help improve oxidative stability. Even adding Vitamin E to Biodiesel in small amounts can help.

ASTM D6217 – Cold Soak Filter Ability Max 360 or 200 seconds
The fuel sample is chilled to a certain temperature, then brought back up to ambient room temperature. The fuel is then passed through a small micron screen. The time the fuel takes to pass through the screen is then measured. This measurement indicates how well the fuel will do in cold weather at gelling up. The standard is 360 seconds for fuel used in temperatures -12 Deg Celcius (about 10 Deg. F) and above. It should take less than 200 seconds for fuel that will be used in temperatures below -12 Deg C. There’s an excellent description of how this test is performed here:

And there you have it! All the tests they perform in the full ASTM D6751-08 Biodiesel test panel! If your Biodiesel can pass all of these tests,  then you’ve conquered the first step it takes to sell Biodiesel commercially in the United States. Europe and other countries have their own quality specifications, but for the most part they’re very similar to the US standard.

Bently Biofuels also has an excellent write-up of the different tests performed and what they may indicate. We highly recommend it.
That page can be found here:

If you’d like to learn more about the ASTM test packages we offer for testing your fuel, visit our ASTM Testing page at:

About Utah Biodiesel Supply

Utah Biodiesel Supply is an industry leader in offering innovative ways to empower our customers to produce Biodiesel. From free online instructional videos on how to get started making this great renewable fuel to promotional items to help our customers proclaim their energy independence, Utah Biodiesel Supply has it covered. With the widest selection available of Biodiesel equipment, supplies, and promotional items, you're sure to learn something new about Biodiesel every time you visit.

One comment on “Biodiesel ASTM Tests (D6751)

  1. Pingback: Making Biodiesel In Cold Weather - Tips & Tricks | Utah Biodiesel Supply Blog

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.