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.
