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Research Suggests Biodiesel Blending is Often Inaccurate; New Radiocarbon Analysis Method Directly Quantifies Carbon of Biological Origin in Blends

While sampling blended biodiesel fuels purchased from small-scale retailers, researchers at the Woods Hole Oceanographic Institution (WHOI) found that many of the blends do not contain the advertised amount of biofuel.

Marine chemist Chris Reddy and colleagues sampled pure biodiesel and blends from more than a dozen distributors across the United States. When testing fuels listed as B20, they found that the actual percentage of biofuel ranged from as little as 10% to as much as 74%. Only 10% of samples met the specifications for biofuel blends required for vehicles of the US Department of Defense, one of the leading consumers of the products.

Reddy and colleagues worked with WHOI senior scientist Bill Jenkins and colleagues at the National Ocean Sciences Accelerator Mass Spectrometer facility to develop an extremely precise radiocarbon-based calibration method for determining if the balance of biofuels and petroleum is correct. The new method relies on the fact that petroleum is “radiocarbon dead” (contains no radiocarbon), while biofuels are enriched with radioisotopes that plants absorb from Earth’s atmosphere and soil.

Error propagation analysis demonstrated that this method calculates absolute blend content with ± 1% accuracy, even when real-world variability in the component biodiesel and petrodiesel sources is taken into account. The researchers independently confirmed this accuracy using known endmembers and prepared mixtures. This is the only published method that directly quantifies the carbon of recent biological origin in biodiesel blends, according to the team.

The calibration method accounts for the differences in chemical makeup of different types of oils, such as canola, coconut, soybean, or animal fats. This method also allows for a direct quantification of the amount of renewable carbon that is emitted from vehicles, which will aid researchers in determining the true environmental value of switching to biofuels.

Reddy and colleagues happened upon the discrepancy while studying the potential effects of a biodiesel spill in the marine environment. The new research was published online on 27 February in the journal Environmental Science and Technology.

Biodiesel blends are often made by local distributors through simple “splash blending,” whereby ingredients are poured together into a container in their respective amounts. The intent is that the simple act of pouring will ensure proper mixing.

But biodiesel is naturally thicker and more viscous than petroleum-based diesel, so it may be settling into separate layers within fuel tanks. Reddy and colleagues also pointed to simple human error—poor math, measurement, or stirring—as a possible reason for the inconsistencies.

The United States currently has a voluntary standard for proper preparation of blended fuels, but no enforcement. The nation does have an enforceable standard for B100 biodiesel, and work on a B20 specification are underway.

The new fuel blending research builds on a 2004-2005 study by the National Renewable Energy Laboratory (NREL) that suggested some national-scale manufacturers were having a hard time producing proper blends of biofuel.



Leo Wells


Put a containerof water under the hood, stick in two electrodes, run one to the ignition the other to a ground. That will generate Hydrogen. Use a tube to supply the motor with Hydrogen.

Electrolisis decompresses the water into Hydrogen & Oxygen Gas. It's that simple to run a car with Hydrogen Fuel.



I don't know if you're getting a kick out of your science spoof, or if you really believe in your perpetual motion machine. If you do believe it go build it; you'll become the richest man in the world. If it's your idea of fun to say stupid things, please stop.

Paul Dietz

Biofuels made from algae grown from CO2 from a fossil fuel plant would have little or no 14C. This method would fail on them. But perhaps the whole point of biofuels is have fuels produced from atmospheric CO2, so maybe that's for the best.


How about who cares whether the mixture is correct. If you're buying B20 at the pump you can run any mixture at that point.

The whole blending concept will only matter for a couple years or until real 2nd gen oils come online.

If we don't get the fossil fuel replacement figured out sooner than later biodiesel will fall back to a small niche market and we will have bigger problems than whether someone got a 10% blend or a 74% blend when they only wanted 20%

Rafael Seidl

@ Paul Dietz -

that's a good point, one that also applies to fossil-based synthetic components like GTL. German engine oils specialist Fuchs recently proposed a system of chemical marker dyes that a special optical sensor in the vehicle would recognize as the fresh oil was added. Marker combinations would uniquely identify each oil product on the market. The ECU would store which oil was added when to eliminate legal hassles if there is ever oil-related damage to the engine or exhaust gas aftertreatment systems. This is especially important in the context of long-life oils or if a DPF is present.

A similar system could also be applied to neat fuel components. Provided the markers are added prior to blending, it would be difficult to cheat. An optical sensor in the fuel filler pipe could then recognize the composition of the fuel as it is added and adjust engine operating parameters accordingly. To prevent engine damage, it could also issue a warning if an incompatible fuel grade is detected.

Note that fatty acid methyl esters (FAME aka biodiesel) tend to slip past the piston rings more easily than conventional diesel. You might have B20 in the fuel tank but the sum of the fuel components suspended in the engine oil may well am amount to a B50 blend. Unfortunately, FAME compounds lead to accelerated degradation of engine oils formulated for conventional diesel fuel. In other words, filling up on biodiesel tends to shorten the required oil change intervals, especially for long-life formulations.


I have wondered if blend at the pump is possible. It had to do more with ethanol, but this might apply as well. You just punch a button that says what percentage you want and there you go.


This is really not that surprising, giving the lax supervision of retail diesel in general. Look at your typical diesel pump...see a Cetane sticker anywhere? Maybe youll see a "40" here and there. If there isnt one there, can it be assumed that this "diesel" cant even meet that standard? 21st century diesel motors that are expected to meet T2B5 aint going to do it with inferior petroD...and any bioD (47 Cetane min) that inevitably gets mixed with this stuff will also suffer a quality perception problem.

Where are the state regulators that are supposed to be enforcing this? Get off your hands.

Is the high price of diesel affected by the export of it, I wonder?

G.R.L. Cowan, hydrogen-to-boron convert

An alternative headline, shorter than "Research Suggests Biodiesel Blending is Often Inaccurate; New Radiocarbon Analysis Method Directly Quantifies Carbon of Biological Origin in Blends":

Shorting by Biodiesel Blenders Caught when Product Found To Be Insufficiently Radioactive

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