1997/08/18 Caterpillar

All Machines Powered By Caterpillar Diesel Machine Engines

In January 1994, a .05 percent limit on the amount of sulfur contained in diesel fuel for on-highway truck engines was mandated in the USA.

NOTE: The removal of sulfur from fuel reduces diesel engine particulate emissions.

Fuel sulfur limits have not generally been mandated for off-highway use. Some local governments do have regulations that include off-highway use. However, there is frequently no difference in the fuel that is sold for on or off-highway use. Other areas of the world are mandating similar limits and due to emission regulations, tighter sulfur limits can be expected in the future.

NOTE: "Lubricity" describes the ability of a fluid to minimize friction between, and damage to, surfaces in relative motion under loaded conditions. Diesel fuel injection systems rely to some extent, on the lubricating properties of the fuel.

Before fuel sulfur limits were mandated, lubricity was generally believed to be mainly a function of viscosity (the degree to which a fluid resists flow under an applied force). When sulfur was removed from the fuel to reduce particulate emissions, lubricity began to be an issue (particularly with lighter fuels, including Jet A-1, JP-8, JP-5, and others. Testing has shown that sulfur, or the lack of sulfur, has no effect on the fuel lubricity. The viscosity of the fuel with lowered sulfur content has not changed.

The most cost effective and commonly used means of removing sulfur from fuel is by a process know as hydro-treatment. Hydro-treatment removes other constituents from the fuel along with the sulfur such as:

* Nitrogen compounds

* Polar materials

* Bi-and polycyclic aromatics

* Oxygen compounds

NOTE: The removal of sulfur from the fuel has shown no detrimental effects on the engine. The removal of polar materials, polycyclic aromatics, and oxygen compounds have lowered the lubricity of the fuel. As a result of lowered lubricity, the fuel is less tolerant of water and dirt contamination. For this reason, it is increasingly important to choose a reputable fuel supplier and to properly maintain the fuel system.

Evaluating injector pump wear from low lubricity can be accomplished by durability tests. Durability tests can typically last for 1000 hours. The durability test is time consuming and cost prohibitive.

There are three recognized lubricity bench tests available:

* High Frequency Reciprocating Rig (HFRR)

* Scuffing Load Ball On Cylinder Evaluator (SLBOCLE)

* Modified ASTM D5001 Scuffing Bocle (SBOCLE)

The International Standards Organization (ISO) has recently approved a fuel lubricity specification. ISO specifies fuel lubricity using the HFRR test, operated at 60°C (140°F). Fuel test results must meet a maximum wear scar of .45 mm (.018 in). The Engine Manufactures Association (EMA) has included a preferred diesel fuel lubricity specification. The new EMA FQP1 Fuel Specification, measures fuel lubricity by the proposed ASTM SBOCLE test. The FQP1 Specification must meet the 3100 g minimum limit. Alternately, the HFRR test at 60°C (140°F) may be used with a .45 mm (.018 in) maximum wear scar limit or 25°C (77°F) .38 mm (.015 in) maximum wear scar limit.

NOTE: There are many after market additives available to treat fuel. Not all additives perform well in all fuel or in all fuel systems. Some lubricity additives may form deposits in the fuel injection system. If lubricity is an issue, consult your fuel supplier for proper recommendations regarding fuel lubricity additives.

NOTE: Caterpillar has adopted the EMA FQP1 lubricity limit as part of the Caterpillar preferred distillate fuels recommendation. See the above chart.