Due to stricter environmental laws and the aiming for high-efficiency technology, more and more tribologically loaded metallic components are being operated at their loading limits. One example from automotive industry are media lubricated high pressure pumps for gasoline direct injection. Injection pressures of about 250 bars are state of the art although it has been shown that higher pressures have a significant influence on the subsequent spray formation and therefore both on the efficiency of the combustion process and the particle emission. However metallic components couldn´t fulfill the tribological demands caused by the increase in pressure. One approach to face the challenges in these highly stressed tribological systems is the application of engineering ceramics. Especially silicon carbide and silicon nitride based ceramics are known for their wear resistance and good frictional behavior in terms of low friction coefficients under media lubricated conditions. A problem that has to be taken into account however are localized regions where poor lubrication conditions up to dry friction may occur.
To investigate the potential of these two ceramic materials for media lubricated high-pressure gasoline injection pumps in particular, model experiments under reciprocating sliding motion were conducted. In these experiments specimens with pellet/plate geometry were used under isooctane lubrication while being loaded with normal loads up to 200 N. In addition to the purely material dependent properties, the influence of specifically designed micro surface textures, applied via laser ablation, was characterized. Focus of research was laid on partial, local velocity dependent texturing as well as on media flow control by channel-like micro structures to assure a sufficient lubrication in all regions of contact.
Joint project: High Pressure Gasoline Direct Injection (HD-BE). Funded by the Federal Ministry for Economic Affairs and Energy (BMWi) based on a decision by the German Parliament.