What is Lubricity?

What is Lubricity?

Starting in the 1990's, diesel fuel has been increasingly more regulated by the US EPA due to the Clean Air Act. In October 1993 the sulfur content of fuel was limited to a maximum of 500 ppm, referred to as low sulfur diesel. The next step was in June 2006 when they limited the sulfur content to only 15 ppm, this was to meet the new emissions standards that included Diesel Particulate Filters and NOx absorbers, this is ultra low sulfur diesel (ULSD)

The EPA mandate to reduce emissions from diesel engines by lowering the sulfur to 15 ppm has prompted studies in regards to fuel pump wear and fuel lubricity. Hydrogen treating (or hydrotreating) is the most common process used by many refineries to reduce the sulfur content of diesel fuels. Sulfur and nitrogen-containing compounds and heavier compounds including heavy aromatics that are natural lubricating agents are reduced or removed under severe hydrotreating. Fuels with reduced levels of these compounds can cause accelerated wear in pump and injection systems. Catastrophic fuel injection failure can occur as experienced in Sweden in 1991 when low sulfur and low aromatics diesel fuel was introduced. Although technology exists that can manufacture injection and pump systems that can tolerate lower lubricity fuels, it is essential that existing fleets that do not have these advanced systems be protected by providing fuel with sufficient lubricity.
Diesel fuel lubricity is a characteristic that has a significant effect on fuel pump wear.
Since the pumps have to be designed with close clearances in the areas where the fuel is being pushed, there is some potential for the surfaces of the pumps to contact, causing wear. Since it is the fuel that is being pumped, the fuel must act as its own lubricant. It has been found that the lubricating properties of the fuel are somewhat enhanced by:

  • The sulfur-containing compounds in the fuel
  • The nitrogen-containing compounds in the fuel
  • Some of the heavier compounds in the fuel (including heavy aromatics)
  • The inherent viscosity (resistance to flow) of the fuel

Since ULSD requirements affect some of these characteristics, the introduction of such fuels has caused lubricity concerns. However, it appears highly likely that greater use of lubricity additives will solve the lubricity problems resulting from diesel fuel hydrotreating.

Lubricity is often tested with the High Frequency Reciprocating Rig (HFRR) and the test results are shown in µm, there are different standards that the fuel has to meet and it is measurable when mixing the available fuel additives to determine the actual lubricity improvements over standard fuel.

In California Propel Fuels has come up with a new option for Diesel owners, Diesel HPR, this is a high performance renewable fuel that meets the ASTM D975 petroleum diesel specification for use in all Diesel engines. This Diesel HPR from Propel offers a higher lubricity than the Diesel No. 2 ASTM D975 fuel that you can buy at the pump. Diesel HPS has a maximum wear scar of 500 µm where standard Diesel No. 2 that has a maximum wear scar of 520 µm. 

DmaxStore recommends to use opti-lube fuel additives as they are some of the best on the market. They offer opti-lube XL (Xtreme Lubricity) that is used to increase the lubricity of the fuel to protect your fuel system from damage that may be caused by the ULSD. 

According to an independent study by Arlen Spicer Opti-lube XPD has a 319 micron improvement, Opti-Lube Summer Blend has a 189 micron improvement, and Opti-lube Winter Blend has a 175 micron improvement over standard No. 2 Diesel fuel.