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This paper looks at the underlying fundamentals of diesel fuel system lubrication for the highly-loaded contacts found in fuel injection equipment like high-pressure pumps. These types of contacts are already occurring in modern systems and their severity is likely to increase in future applications due to the requirement for increased fuel pressure. The aim of the work was to characterise the tribological behavior of these contacts when lubricated with diesel fuel and diesel fuel treated with lubricity additives and model nitrogen and sulphur compounds of different chemical composition. It is essential to understand the role of diesel fuel and of lubricity additives to ensure that future, more severely-loaded systems, will be free of any wear problem in the field.

The Co-ordinating European Council (CEC) for the development of performance tests for transportation fuels, lubricants and other fluids has set up a working group to develop a laboratory pump rig test able to discriminate between diesel fuels of different lubricity performance. This test was expected to correlate with the performance of fuels and Fuel Injection Equipment (FIE) in the field, therefore providing a way to avoid costly field trials. This test could also enhance the understanding of the results from the High Frequency Reciprocating Rig (HFRR) method. The CEC working group was supported by representatives of Oil Companies, Test Houses, Additive Companies and all the European FIE Manufacturers. After a thorough investigative phase, the group focused on a Bosch VE 4 distributor-type pump run according to the Bosch WP2 test cycle. This choice was also widely accepted throughout the industry.