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. The standard Ball-on-Cylinder Lubricity Evaluator (BOCLE) test method as well as a modified version of this test were used. In a cooperative test between Chevron Research and Technology Company and Stanadyne Automotive Corp., pump stand testing was also conducted to characterize the low sulfur fuel. The addition of sulfur had no positive effect on fuel lubricity and, in some cases, had negative effects.