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Federal regulations require all highway diesel fuel to have a maximum sulfur level of 500 ppm, effective October 1993. California regulations require a maximum 10% aromatics content in addition to the low sulfur content. The hydrotreating processes used to reduce fuel sulfur and aromatics contents to meet these new regulations have the potential of reducing fuel lubricity by reducing the amount of polar impurities such as nitrogen compounds which provide lubricity. This is a great concern for many fuel injection equipment suppliers and fuel producers. Several low aromatics diesel fuels were produced in a pilot plant facility and analyzed using a Ball-on-Cylinder Lubricity Evaluator (BOCLE). These fuels were then tested in a pump endurance test facility using two types of fuel-lubricated rotary-distributor fuel injection pumps.

The sulfur content of all highway diesel fuel was required to be reduced to a maximum of 0.05 wt % starting October 1993. This federal requirement results in further fuel processing by refineries. The hydrotreating process used to reduce fuel sulfur has the potential to reduce the fuel's lubricating characteristics. Fuel producers and fuel injection equipment suppliers have been concerned about the likelihood of increased component wear upon the introduction of these new fuels. Low sulfur fuels have been produced and marketed in Southern California since 1985 with no apparent evidence of any field problem. Nevertheless, concern outside of this area exists. Therefore, one such fuel with a sulfur content well below 0.05% was used to conduct a vehicle test to evaluate its effect on the fuel injection pump. This fuel and a low aromatics diesel fuel were used to investigate the effect of various levels of two different sulfur compounds on the lubricity characteristics of the fuels.