Characterisation of the chemical classes present in diesel fuel to identify the components that contribute to lubricity

Abstract

Lubricity is the ability of a substance to prevent wear in a system where interacting surfaces are in close contact with each other. Some critical components in high pressure diesel injection systems are dependent on diesel fuel for lubrication and thus the lubricating properties of diesel fuel are very important. The relationship between the chemical composition and lubricating properties of diesel fuel were investigated, in an attempt to identify chemical classes and components in diesel that could improve lubricity. From literature, hetero-atom containing compounds and aromatic hydrocarbons were thought to be important. The chemical compositions of diesel fuels were determined using comprehensive twodimensional gas chromatography coupled to time of flight mass spectrometry. Four different column combinations were investigated and compared for the separation of these samples. The separations obtained for each column combination were compared graphically and mathematically. Better compound separation was achieved as the polarity of the stationary phase in the first dimension increased. Using a column with an ionic liquid stationary phase in the first dimension presented unique separations of aliphatic hydrocarbons but the improved compound separation resulted in the overlap of certain compound classes. The best class separation was achieved by using a polyethylene glycol column in the first dimension. Multivariate statistical analysis was used to investigate the relationship between the chemical compositions and the measured lubricities of these fuels. A provisional model was determined, which showed that lubricity improved as the relative amount of aromatic hydrocarbons and oxygenates increased. The model also showed that oxygenates play a more important role than aromatic hydrocarbons in improving lubricity. The influence of chain length was also investigated and less volatile oxygenated compounds seem to contribute more to lubricity.