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The problem with diesel – Part 2

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World Coal,

The first part of this article looked at the problems presented by the use of ultra-low sulfur diesel. In this part, Michael Holloway, Certified Laboratories, US, looks at the effects of ultra low sulfur diesel on heavy-duty diesel engines.

Less lubricating
In 1993, low sulfur diesel (less than 500 ppm sulfur) was six times drier, or less lubricating, than standard diesel fuel (less than 3000 ppm sulfur). This reduction in sulfur (the natural lubricant in diesel fuel for injector pumps and injectors) has been found to cause dramatic wear and failure.

The new ULSD is 33 times drier than today’s low sulfur diesel. Because ULSD is so dry, wear in injection systems could become a major problem. Premature wear in injection systems results in failure and replacement. It also results in reduced fuel economy, because worn injectors produce poor fuel spray patterns and can allow too much fuel into the combustion chamber.

Low aromatic content
The effects of low aromatic content (10% or less) are yet to be understood. Most engine manufacturers have replaced old seals with shrink resistant seals in injector pumps and injectors. However, other elastomers in the fuel system may be affected.

Increase in cetane
The increase in cetane to 48 is a welcome improvement and will help to reduce emissions, improve starting time and aid in combustion that is more complete. However, this increase in cetane still does not meet the requirements of the Engine Manufacturers Association for minimum cetane rating of 50. Cetane is rated on a scale of 30 to 60; a cetane rating of 50 or higher is highly preferred over a cetane rating of 48.

Reduction of fuel economy.
A comprehensive study by Volvo Truck Corp. reported in Fleet Owner Magazine that the reduced energy density of ULSD results in a 2% reduction in fuel economy compared to regular low sulfur diesel. That is because the refinery process used to remove the sulfur reduces the actual weight of the diesel fuel by 1.5%, resulting in less energy per gallon of fuel. This news comes at a time of record fuel prices and will cost customers at least US$ 0.04 – 0.06/gal in reduced fuel economy.

A host of issues with ULSD
Lubrizol, one of the world's largest raw material refinery additive manufacturers recently conducted a webcast that focused on many of the forthcoming problems associated with the new diesel fuels ULSD and biodiesel. As part of this webcast, John Taracha, the company's product manager for refinery and oilfield products, stated that:

  • New ULSD fuels have lower lubricity, lower oxidation stability, lower conductivity (static electricity safety concern), poor cold flow, lower density (translates to energy) and less solvency (means more waxy deposits).
  • ULSD has less solvency, which means more paraffin (waxes), resulting in increased deposit formation.
  • ULSD has more acidic characteristics compared to previous high sulfur diesel.
  • Ultra-low sulfur kerosene (ULSK), which is used to blend with diesel for low temperature applications, will be very difficult to obtain during 2013.
  • The new fuels will pick up storage tank water-bottoms and other contaminants in the water when it is first introduced.

The final part of this article looks at the use of biodiesel as an alternative diesel fuel and the benefits of using a fuel treatment programme.

Written by Michael Holloway, Certified Laboratories, US.

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