Within the cluster of excellence “Tailor-made Fuels from Biomass” at RWTH Aachen University new biofuels are developed and investigated. Because common-rail injection pumps are generally lubricated by the fuel itself, the tribological characteristics of the fuel candidates is of interest. The lubricity and viscosity of the alternative fuels differ from diesel. Hence, a reliable function of the tribological contacts, which are designed for the operation with diesel, cannot be guaranteed. To achieve a reliable operation even for fuels with, for instance, a lower viscosity or worse lubricity an optimisation of the tribological contacts is necessary.
The focus of the investigations presented in this paper lies on the piston-cylinder-contact. Prior to the simulative study the losses in a pump operating with various fuel candidates are quantified by means of efficiency measurements. By these measurements the great impact of the fuel’s rheology on the pump performance is clarified.
Based on detailed EHD-simulations with various fuels under typical operating conditions, an optimisation of the piston-cylinder-contact is presented. The optimisation aims for the reduction of solid friction by changing the pressure field on the piston. The approaches can basically be separated into grooved and contoured pistons. The potential of the different approaches is discussed based on simulation results and effects, which occur in the lubricating film of the optimised contacts.