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How will ultra-low sulfur diesel affect data center generator performance?

While ultra-low sulfur diesel (ULSD) fuel is a boon for the environment, it could negatively affect your data center generator performance and lead to equipment failure.

The Environmental Protection Agency (EPA) is partly responsible for a revolutionary transformation of the diesel engine industry by mandating cleanup of diesel fuel. The program was a tiered implementation of standards to gradually reduce the sulfur content in diesel fuel from more than 3,000 parts per million (ppm) down to 15 ppm in ultra-low sulfur diesel (ULSD) fuel. Almost every country worldwide is participating, and there is promise that this will benefit the planet through avoidance of millions of tons of harmful diesel emissions.

Most of the attention to ULSD is going in the direction of the green initiative and how wonderfully clean diesel has become. For those of us working in the data center industry, USLD poses a low-probability threat to uptime, but there may be a high degree of fallout if failure occurs.

The process to refine diesel into ULSD affects the chemical properties of the product. The upsides of this process, known as hydro treating:

  • Removes sulfur
  • Virtually eliminates aromatic properties
  • Diminishes lubricity
  • Lowers conductivity
  • Reduces energy density

The possible downsides of hydro treating:

  • Increases fuel leaks
  • Reduces conductivity
  • Lowers economy
  • Extends drain intervals
  • Raises fuel cost

Potential risks of ULSD in the data center
Leaks. ULSD could cause injector fuel pump leaks and O-ring failure. Aged seals may shrink, and if there is reduced elasticity in seals they may not adapt to the change to ULSD.

Reduced lubricity. The fuel system is negatively impacted and there seems to be an increase of particulate matter. There is a known clogging of fuel filters when ULSD is introduced. Some fuel injector and fuel pump failures may be attributed to the new product as well.

Conductivity. ULSD has less conductivity than conventional diesel. With lower conductivity, it is more likely to collect an electric charge. Facility managers need to be assured that proper grounding is done during fuel delivery.

Reduced energy. There is less BTU in ULSD and less power will result. There is also a reduction in MPG.

Increased cost. The EPA says the added cost of production for ULSD is about 7 cents per gallon, while my consumer survey reveals 20 to 25 cents per gallon by the time it is dispensed at the pump.

Most of the attention to ULSD is about how clean diesel has become. For those of us in data centers, there may be a high degree of fallout if failure occurs.

Please know that the problems presented are not absolute in nature. The fact is that failures were seen across the country in different climates and in a variety of equipment. The researchers have not pinpointed specific equipment manufacturers, models or climate conditions to aid in identifying specifics, although colder climates may see a higher rate of incidents. It is clear that the introduction of ULSD had caused these difficulties, which are well beyond what is normally seen in the many industries reporting problems with ULSD use.

There is a new game in town -- it is about efficiency, energy conservation and a green initiative. Your data center emergency generator has new fuel -- it is less powerful than the old fuel, it offers reduced lubricity, there are new opportunities for failure and you get less MPG than you are accustomed to. ULSD can reduce the response time of your data center's emergency generator by as much as 5% when called to take over near-capacity loads in emergency situations. Consider the history of your generator repairs, maintenance record, the credentials of your service provider and the age of your emergency generator. Refineries are trying to compensate for many of these concerns by formulating new additives, but this continues to be a learning experience.

It's expected that the U.S. market will distribute about 60 billion gallons of ULSD in 2010. The market consists of about 70% highway diesel use, 6% railroad and marine use, 14% home use, and the remaining 10% for non-road use. The data center user community sits someplace within the non-road use. I present this because it has been difficult to draw attention to such a small piece of the pie.

Some crucial takeaways from this include the need for a heightened awareness of grounding safety during fuel delivery; increased diligence in visual inspections of your emergency generators -- especially for fuel leaks, checking and replacing filters and spare filter availability; and the importance of knowing the contents of your fuel tank, understanding the additives used, and testing emergency generators. I suggest block-load and step-load testing, and retro-commissioning will check the performance of your emergency generators. ULSD is a grand opportunity to validate the performance of the emergency generators that support your data center.

ABOUT THE AUTHOR: Bob Doherty makes it clear that he is not an engineer -- he is a data center manager with more than 40 years of experience. He is the founder and president of OMS in Your Data Center LLC, which primarily focuses on data center energy conservation best practices. Send Bob an email at and check out

What did you think of this feature? Write to's Matt Stansberry about your data center concerns at

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