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Ultra Low Sulfur Diesel 101

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Emissions Standards Continue to Tighten

You may have heard that The U.S. Environmental Protection Agency has adopted a tough set of diesel emissions standards aimed at drastically reducing the sulfur content of diesel fuel to improve air quality. A good thing indeed.

To meet those standards, petroleum refiners are producing Ultra Low Sulfur Diesel (ULSD) or S15, a cleaner diesel fuel that has a maximum sulfur content of 15 parts per million (ppm). When the full retail phase-in is complete, this fuel will be a direct replacement for Low Sulfur Diesel or S500 (which has a sulfur content of 500 ppm) culminating in more than a 95% sulfur reduction.

In a move similar to eliminating lead from gasoline to protect catalytic converters, sulfur reduction in diesel fuel is necessary to preserve the proper function of the advanced emissions control systems on new diesel engines. The combination of this cleaner burning fuel and the sophisticated emissions devices on the new engines will result in more than a 90% reduction in soot and oxides of nitrogen.

Look for the Label

Beware 2007 vehicle owners: Not all retail outlets (excluding California) are required to offer ULSD fuel until December 1, 2010. For a period of time, through this transition period, some fueling stations may not have ultra low sulfur diesel (ULSD) available. The pumps must have a label stating that they dispense ULSD, so if the label isn't on a pump, don't put the fuel in your 2007 vehicle—severe damage to the emissions control systems could result. Find a station that has ULSD to fill your 2007 vehicle.

Please note, however, that all diesel fuel in California was transitioned to ULSD by September 1, 2006, and no labeling is required.

But Can I Use ULSD in My Older Diesel Car?

All 2007 and later diesel vehicles sold in the U.S. for on highway use will be required to use ULSD. No problem here, these engines are designed to run on this fuel. But what about older engines—engines that were designed to run on Low Sulfur Diesel (S500) or its very early brother, S5000?

The argument here certainly isn’t in defense of higher sulfur fuel—its many drawbacks are quite evident. But sulfur in the fuel enhances lubricity, and older engines depend on it to protect their pumps and injectors from premature wear. To combat the loss of this lubrication, packages of additives that increase lubricity will be blended with the fuel prior to distribution.

Biodiesel to the Rescue

While synthetic additives will initially fill the role of lubricant, there is plenty of room for development of biodiesel blends that can easily handle the task. Because of its vegetable oil base, biodiesel contains no sulfur and has a very high lubricity factor. These two qualities make it an ideal candidate for blending with ULSD to solve the problem of lubricity while keeping the sulfur ratio intact.

Stay tuned. Biodiesel started out as a niche fuel touted mainly by environmentalists and the agriculture industry, but it is proving to be quite useful as an additive as well as transitional fuel while cleaner alternatives continue to be developed. For it pure versatility—as a straight fuel, and as a multifaceted additive—biodiesel has certainly earned its stripes.

Clearly the advantages are compelling, but as with any transition from one technology to another, there are hurdles to be cleared. Mainly it boils down to logistics. It will take time to develop the blends that perform well under various conditions (cold flow characteristics, adequate lubricity, fuel efficiency) and to get the blends into the infrastructure pipeline.

Cold Weather Considerations

The refining process used to attain the sulfur ratio of ULSD affects the naturally occurring paraffins (wax) inherent in diesel fuel in such a way that can cause the fuel to gel more readily in cold temperatures.

Though most retail fuel should be properly winterized for your local climate, some testing and experimenting with additional treatment processes will probably be in order. Higher doses of anti-gel additives may be necessary for extremely low temperatures—and not all additives that have traditionally been used for treating conventional low sulfur diesel will be compatible with—or effective on—ULSD.


Keep the Following Points In Mind:
  • First look for packaging labels that indicate compatibility with ULSD.
  • Secondly, be aware that mixing conventional low sulfur kerosene with ULSD as a flow enhancer will increase the sulfur ratio and could damage emissions control equipment.
  • Finally, even in cases where it is available—cutting ULSD with ultra low sulfur kerosene may be ineffective as a flow enhancer.

Please note: This article is aimed for the on-highway usage portion of the diesel emissions regulations. The actual legislation encompasses all uses of diesel fuel, including agricultural, marine and non-highway usage such as railroads.

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