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Many components on both aircraft and ground vehicles rely on fuel for lubrication and cooling of sliding contacts. Reliable performance of these power sources depends on the fuel providing sufficient lubrication to protect each of the many contact types within the pump and injection system. This characteristic of fuel has come to be known as lubricity. The subject of fuel lubricity has gone through a number of phases, most of which resulted from changing the composition of the fuel, which historically has been driven by fuel stability and by environmental regulations. This paper reviews these phases in chronological order. Beginning with the fuel system failures reported in aviation equipment in the 1960s and 70s, through the Military experience with low lubricity kerosene fuels in compression ignition engines in the 80s and 90s, to the ongoing introduction of more severely refined diesel fuel in progress in many developed countries around the world.

The average oil change interval for passenger vehicles in the USA is gradually increasing, and is currently approaching 8,320 km (5,200 miles). This paper details the results of lubricant condition monitoring on samples taken from hundreds of vehicles at intervals ranging from 0 to 25,600 km (16,000 miles). The data indicate steady additive depletion by 4,800 to 9,600 km (3,000-6,000 miles), resulting in a concomitant decrease in measured oxidation resistance. Oxidation and nitration of the basestock was also found to be present at this point, resulting in a gradual increase in both kinematic and HTHS viscosity. As a result, it is predicted that excessively long drain intervals will produce a measurable increase in fuel consumption and associated CO2 emissions. Many owners' manuals recommend service intervals of 12,000 and 4,800 km (7,500 and 3,000 miles) under “normal” and “severe” service conditions, respectively.