How will diesel fuel properties, other than sulfur, change with S15 (ULSD)?

There are several diesel fuel properties other than sulfur that will change as a result of moving to S15 (ULSD).

* Lubricity:Lubricity is a measure of the fuel's ability to lubricate and protect the various parts of the engine's fuel injection system from wear.The processing required to reduce sulfur to 15 ppm also removes naturally-occurring lubricity agents in diesel fuel. To manage this change the American Society for Testing and Materials (ASTM) adopted the lubricity specification defined in ASTM D975 for all diesel fuels and this standard went into effect January 1, 2005.
* The D975 specification is based on the High Frequency Reciprocating Rig (HFRR) test (D 6079) and requires a wear scar no larger than 520 microns.


* Energy Content:In general, the processing required to reduce sulfur to 15 ppm also reduces the aromatics content and density of diesel fuel, resulting in a reduction in energy content (BTU/gal).
* The expected reduction in energy content is on the order of 1% and may affect fuel mileage.


* Cetane Number:In general, the processing required to reduce sulfur to 15ppm also reduces the aromatics content resulting in an increase to the cetane number.

There are some potential drawbacks to using ULSD fuel. These drawbacks include cost, availability, lubricity, and cold flow properties. At this time, the cost of ULSD is difficult to estimate due to the fact it is not available in Colorado. EPA estimates “that when fully implemented the sulfur reduction requirement will increase the cost of producing and distributing diesel fuel by about five cents per gallon.” Other sources indicate this cost per gallon will be higher. This increased cost is due to additional refining costs to remove the sulfur from the fuel. Another issue hindering the widespread use of ULSD at this time is the availability of the fuel. Currently the fuel is available in limited parts of the country, primarily on the east coast. At this time, the fuel is not available in Colorado.

The process used to refine ULSD also results in a loss of lubricity, which could potentially result fuel system component wear. However, additives or blending ULSD with biodiesel increases the lubricity of ULSD. Puget Sound Clean Cities reports that they have not encountered any problems with ULSD when properly formulated with additives or biodiesel. Other potential issues with ULSD are the cold flow properties. In cold weather, the cloud point of ULSD is higher than conventional diesel. Therefore, ULSD may require added precautions, such as additives or heated storage tanks, when the ambient temperature gets very low.

The Lubricity Question
The buzzword around the ULSD issue is definitely lubricity. Without lubricity additives—which include biodiesel—ULSD would be hard on diesel engines, Mannato says. Early discussions about the biodiesel industry cornering the market as a lubricity agent have died down, but are not totally muted. Biodiesel might be able to fill niche markets as a lubricity agent, Nazzaro says. In the near term, however, most industry experts say synthetic lubricity additives will dominate.

Cost is one factor. Conventional lubricity additives are competitively and consistently priced, while the price of biodiesel is based on supply and demand, and is prone to greater fluctuations. To be attractive as a lubricant, biodiesel needs to be priced lower than diesel fuel, Nazzaro says.

The blend rates for chemical lubricity additives—often measured in parts per million—also come into play, Noyes says. It’s generally considered easier to achieve desired ULSD lubricity levels with synthetic additives than with biodiesel. Simply stated, it takes less synthetic additive, on a gallon-for-gallon basis, to get the job done. To use biodiesel as a lubricity solution nationwide would require additional storage capacity.

Capacity is another issue. Currently, there just isn’t sufficient biodiesel production to fulfill even a 1 percent blend for the entire U.S. diesel supply. “The (biodiesel) model is just not mature enough to be counted on as a lubricity agent,” Nazzaro says.
Nazzaro believes the oil industry may be willing to look at the alternative fuel more closely in the future. Consistency, quality and reliability will remain the crucial factors, the last of which, some say, would require biodiesel to be available at almost every terminal in the United States.