Editor's Note

Seeing the ULSD Glass Half-Full
By Tom Bryan | November 10, 2006
There's a thin line between pragmatism and pessimism, and I may have crossed it in early 2006 when I wrote a somewhat biting op-ed piece about the perceived potential of biodiesel as an ultra-low sulfur diesel (ULSD) blending agent.

In my March Editor's Note, "Has Biodiesel Already Missed the ULSD Boat?," I pointed out that from what I heard at the 2006 National Biodiesel Conference and Expo, biodiesel was by and large not being used as a ULSD lubricity additive or a dilutor for off-spec fuel. During one session at the conference, at least three refiners said they had no plans to use biodiesel for either purpose. Focusing on that lowlight, I proceeded to question those in the industry who propagated a seemingly artificial hope. I wasn't wrong-specialty additives are still beating out biodiesel in this area-but there were some emerging positive peripherals just over the horizon that I falied to recognize.

This month, Biodiesel Magazine Staff Writer Ron Kotrba sheds light on what may be the most encouraging news about biodiesel's compatibility with ULSD. In his page 40 feature, "Are DPFs Better with Biodiesel?," Kotrba speaks with researchers who say B100 and biodiesel blends offer significant advantages over ULSD when it comes to the operational efficiency and proper functioning of diesel particulate filters. The story builds upon National Biodiesel Board CEO Joe Jobe's October "NBB In Sight" column, in which he highlighted a National Renewable Energy Laboratory (NREL) study that tested B5 and B20 blended with ULSD, with and without DPFs. What Jobe pointed out last month, and what Kotrba's story details this month, is that biodiesel helps to reduce the temperature at which particulates are burned off in the soot trap, lowering backpressures caused by a plugged DPF.

Part of the DPF's job is to alter the composition of nitric oxide in exhaust to nitrogen dioxide. That's beneficial because nitrogen dioxide is a more efficient oxidizer of particulates than air, so increasing the concentration of nitrogen dioxide via the oxidation of nitric oxide-whether that's with an oxidation catalyst upstream from a DPF or a catalyzed DPF-lowers the temperature needed to burn off the soot effectively. It appears that biodiesel enhances the "burn-off" of collected soot-a process of regeneration-and it keeps the filter from plugging and compromising vehicle performance.

B100 yields an extreme enhancement of oxidation while the effects of B20 are appreciable, too. Researchers are still trying to determine what the "threshold impact" is-or how low a biodiesel blend may be and still appreciably boost oxidation. Initial data is hopeful, though, as the NREL report concludes that biodiesel causes a significant increase in regenerate rate, even at the 5 percent blending level.

Furthermore, researchers are discovering that by lowering the temperature at which oxidation can take place, biodiesel use leads to lower fuel consumption and less engine wear.

There's a small caveat on this pile of delightful data. As Kotrba's article mentions, the polarity of biodiesel when mixed with ULSD-especially at the B20 level-has an antagonistic effect on the formation of deposits. Researchers say that if complete transesterification of the renewable fuel is not achieved, the ramifications can be pretty negative. It's one more critical reason the industry needs to be ultra-vigilant about fuel quality.
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