ASTM approves low-metals grade in B100 biodiesel specification D6751

Based on compelling new biodiesel fuel-quality data from some of the nation’s top research institutions, ASTM International has approved a new low-metals (LM) grade of biodiesel in D6751, the ASTM specification for low-carbon B100 biodiesel used as a blendstock with middle-distillate fuels such as diesel fuel.

The new performance standard bolsters confidence in the fuel for original equipment manufacturers (OEMs) and fleets, providing further evidence that biodiesel fuel quality is high, continually improving and meeting robust quality standards.

Throughout its 30-year history, the biodiesel industry and Clean Fuels Alliance America (previously known as the National Biodiesel Board) have proactively led cooperative research projects with OEMs and leading research institutions to determine if ASTM specifications for B100 needed to be modified to ensure biodiesel blends would perform reliably and effectively when diesel fuel or diesel-engine regulations changed.

This latest round of research followed that same strategy to test the impacts of B20 on the long-term durability of diesel particulate filters in new technology diesel engines (NTDEs) outfitted with modern aftertreatment systems, including selective catalytic reduction (SCR) and diesel particulate filter (DPF) units.

This recently completed research was conducted with Southwest Research Institute and the National Renewable Energy Laboratory in a large, multiyear cooperative program with engine and aftertreatment OEMs.

The testing compared long-term (over 1,000 hours of accelerated aging) impacts of NTDEs running on B20 with a lower level of metals—equivalent to B100 containing a total of 4 parts per million (ppm) for sodium, potassium, calcium and magnesium—to the impacts of conventional ultra-low sulfur (ULSD) diesel.

The results indicated that biodiesel containing a maximum of 4 ppm total metals resulted in ash that was similar to that deposited by ULSD, exhibited a similar ash-cleaning removal efficiency, did not have a negative effect on DPF pressure drop or regeneration rates, and did not appear to have any deleterious physical effects on the DPF substrate.

These studies were recently presented at the SAE Congress in Detroit in April and published as SAE papers 2023-01-0297 and 2023-01-0296.

The work was instrumental in the passage of a successful ballot by the ASTM D02 Fuels Committee to approve a new LM grade of ASTM D6751 biodiesel with a maximum of 4 ppm total metals (Na+K+Ca+Mg), down from the existing grades that allow up to 10 ppm total metals.

A final contributing factor to the persuasive technical data required to modify ASTM specifications has been the biodiesel fuel-quality report published by NREL.

Now in its fifth year, this annual report documents the quality of biodiesel produced in the United States and Canada by BQ-9000-certified producers, which represent over 90 percent of North American production.

According to the most recent NREL report from June 2022, the current average of B100 total metals in the marketplace today registers below 1 ppm total, well below the 4 ppm specification recently adopted in the new LM grade of biodiesel at ASTM.

“The annual BQ-9000 quality reports demonstrate general compliance with this new low-metals grade by the industry, even today,” said Scott Fenwick, technical director for Clean Fuels. “Soybean growers, through the soybean-checkoff program, continue to invest in fuel quality and engine testing to provide more confidence to engine manufacturers and fleets that biodiesel is fit for purpose in the diesel engines of yesterday, today and tomorrow, and will have only positive impacts on performance and durability.”

The rigor of these cooperative research efforts and the positive results, along with the already low level of metals in commercial production in the field, bode well for biodiesel use in the new ultra-low emissions diesel engines (ULEDE) coming to market in 2027-’31.

Clean Fuels will continue to work closely with ASTM International, OEMs, and leading research institutions to ensure that B20 and higher biodiesel blends continue to offer fleets an easy, reliable and sustainable decarbonization solution now and for decades to come.

As ASTM International celebrates its 125th anniversary this year, it has chosen the ASTM D6751 specification for biodiesel as one of the Top 10 most-influential standards that ASTM has ever produced.