Impact of biofuel lubricity on wear in highly loaded contacts

The ability of a fluid to affect friction and wear in a tribological system that operates in the regime of boundary lubrication is known as lubricity. This work studies the influence of selected molecular features on lubricity on the basis of experimental studies performed with a High Frequency Reciprocating Rig (HFRR). First the chemical and tribological background for the regime of boundary lubrication are presented with special emphasis on the tribological system of the HFRR test. In addition to the standardised evaluation procedure, a three-dimensional evaluation of the worn specimens and a consideration of the friction between the two specimens takes place. For the investigation of the molecular characteristics first the wear behaviour in the HFRR test is investigated. To do so, the influence of the test parameters on the test results is considered with selected fluids. Distinct wear patterns can be recognised when examining a wide range fluids with different lubricities. Three principal wear types are introduced to describe and analyse the patterns. On the basis of the experimental results, a discussion of the tribological origin of the different wear patterns and their effects on lubricity measurements is given. Based on this preliminary work, the relationship between certain molecular characteristics and the lubricity of potential biofuels and similar molecules is investigated. These investigations include comparative studies on the influence of the spatial molecular structure and various functional groups is considered