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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 high frequency reciprocating rig (HFRR) was developed in the early 1990s as a test method to assess diesel fuel lubricity in order to provide wear protection for fuel injection pumps. This was necessary in response to the many field failures that occurred following the introduction of ultra-low sulphur diesel in Sweden. The prevalent fuel injection equipment (FIE) technology at this time utilised rotary pumps capable of reaching maximum fuel pressures of ∼650 bar in systems for direct injection engines. The continued drive for efficiency led to many changes in FIE technologies, materials and pressures. Modern high pressure common rail pumps reach significantly higher pressures, with 2200 bar available today and pressures up to 3000 bar discussed in the industry.