By Paul Abelson
senior technical editor
As Katrina's impact on prices at the diesel pump faded, the New Year brought new fuel concerns to truckers, and some of the most common questions being asked involve ultra-low-sulfur diesel.
Recently, one reader put it this way: "My fuel supplier tells me that in 2006 we're going to have to use a new, lower sulfur diesel. He says it's going to cost more. I remember the last time we changed sulfur, it screwed up a lot of engines. Will it do that again? How much is it going to cost? What's the risk using it and why do we have to keep changing anyway?"
Many of you, no doubt, have similar memories of the large price jump and the engine problems that occurred in 1998. That's when sulfur content was capped at 500 parts per million, a huge drop from the 3,000- to 5,000-ppm fuels in use before the change.
However, the problems many truckers experienced had more to do with fuel chemistry than sulfur content. Diesel is a non-uniform mixture of hydrocarbons, refined from compounds distilled from crude petroleum. They are similar to jet fuel, kerosene and home heating oil.
In 1998, the California Air Resources Board believed that the changeover in sulfur content presented an opportunity to change the balance of paraffinic and naphthenic molecules to a greater degree than the EPA-mandated fuel.
Naphthenic molecules are like hexagons joined together in tight bunches. They resist gelling, but evaporate more easily and are more difficult to burn completely. Paraffinic molecules look like a string of plus signs. They burn more clearly, but tend to gel more easily.
CARB went for the cleaner, more complete combustion. What the board didn't consider was that many elastomer seals in fuel systems take a set according to the fuels used. When the balance of molecules changed, seals reacted, dried out and cracked.
Once damaged seals were replaced, new ones adjusted to the new fuels and haven't given any trouble since. Molecular balance, not sulfur content, was the cause of those problems.
Ultra-low-sulfur diesel has actually been in service since 1999. In California, for instance, 15-ppm sulfur fuel is sold as Environmentally Clean Diesel at BP's ARCO stations, and from many other brands. Fleets operating with ULSD report fewer maintenance problems and better oil analyses, allowing extended oil drain intervals.
In limited quantities, tankers deliver ultra low sulfur diesel, but when it is in every fuel stop, it must go through pipelines. Pipelines alternately carry different fuels, including high-sulfur fuels like jet fuel. Residual sulfur can contaminate the ultra-low-sulfur diesel. Pipeline operators want fuels entering the pipeline to have 8-ppm sulfur or less to keep delivered fuel within limits. That will raise prices more than the nickel per gallon that the EPA projected, perhaps as much as 15 cents per gallon.
The EPA will allow refiners to ship up to 20 percent of their volume as 500-ppm LSD into 2007. Major refiners will be supplying only ultra-low-sulfur diesel into the supply system by June 1 this year, the deadline for supplying 15-ppm fuel into distribution. Smaller ones will continue to refine LSD. Given time to go through the system, the deadline to start selling ultra-low-sulfur diesel is Oct. 15 this year.
If you have a pre-2007 engine, and can find 500-ppm low sulfur diesel, you can still use it legally. But for a new truck, you'll need the ultra-low-sulfur version.
Ultra-low-sulfur diesel is necessary because of EPA's extremely clean standards for diesel engine exhaust. The only way to meet the 2007 and 2010 standards is with exhaust after-treatment, devices, downstream of turbochargers. Catalytic converters (handle NOx) and diesel particulate filters (DPFs) can be "poisoned" by gases and acids produced when sulfur burns. Sulfur in exhaust also contributes to acid rain. ULSD prolongs devices' effective life.
Paul Abelson may be reached at firstname.lastname@example.org.