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The problem with diesel – Part 1

Published by
World Coal,

Michael Holloway, Certified Laboratories, US, looks at the problems presented by the use of ultra-low sulfur diesel.

Diesel fuel can be a major expense and in recent years it can contribute to costly downtime and components failure. The quality of diesel fuel has declined within the past few years. There are several reasons for this declination. Rougher grades of crude are being extracted, forcing producers to take shortcuts in the refining process in order to maintain the same gross profit margins. The best parts of the crude fractions are being used to produce jet fuel, kerosene and unleaded gasoline. Emission laws that came into effect in 1993 have sought to reduce the amount of sulfur found in petroleum products. Sulfur is a natural anti-wear and biocide compound and, therefore, a reduction in quality has lead to a dramatic increase in engine component wear and microbial infection of the fuel.

ULSD fuel problems
For these reasons, the quality of diesel fuel has been compromised resulting in:

  • Reduced cetane levels: this contributes to a decrease in ignition performance, an increase in starting time and detonation wear, and an overall increase in the amount of dollars per litre spent to achieve a performance power level.
  • Increased friction and wear: injector, pump and cylinder wear will increase due to reduced lubricity.
  • Water contamination: this will contribute to rust and corrosion of fuel tanks, lines, and engine components.
  • Fuel oxidation: which will lead to the formation of gum, varnish, lacquer and carbon coke on injectors, valves, pistons, and liners.
  • Increased emissions: NOx, carbon monoxide, hydrocarbon and particulate emissions will all be increased.

EPA regulations on air pollution have been the driving force behind most of the changes in diesel fuel and diesel engines since 1993. In 1993, the sulfur content of diesel fuel was reduced from an average of 3000 ppm to 500 ppm. The aromatic content was also reduced to 35%. These changes resulted in many serious maintenance problems for diesel injection systems. Sulfur in diesel fuel is the natural lubricant for diesel fuel injection systems, as well as fuel pumps. This reduction in sulfur content caused wear on the systems to increase to five times previous levels. The reduction in aromatics caused seals in fuel pumps and injectors to shrink and leak.

These problems occurred in addition to the normal diesel problems, such as low cetane, water, contaminants and biological growth. From on 1 June 2006, refiners started producing ultra-low sulfur diesel (ULSD) with a sulfur content of no more than 15 ppm. ULSD had to be in the hands of retailers no later than 1 September 2006.

ULSD has to comply with the following specifications:

  • 15 ppm or less of sulfur.
  • Minimum levels of 48 cetane for large refiners and 47 cetane for small refiners.
  • No more than 10% aromatics.

These specifications are the same as those required by the California Air Resources Board (CARB) for several years and by the Texas Natural Resource Conservation Commission since 1 October 2005. The June 2006 date was the national implementation date for ULSD.

The second part of this article looks at the effects of ultra low sulfur diesel on heavy-duty diesel engines.

Written by Michael Holloway, Certified Laboratories, US.

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