The advent of low-sulfur petrodiesel fuels has raised concern about the inherent lubricity of these fuels. It has been shown that these fuels possess poorer lubricity than their non-desulfurized counterparts, largely due to the removal of polar oxygen- and nitrogen-containing compounds in these fuels. Biodiesel, an alternative diesel fuel derived from the transesterification of vegetable oils or animal fats, possesses inherent lubricity. It has also been generally accepted that biodiesel can restore lubricity to low-sulfur diesel fuels at blend levels of 1-2% biodiesel in the petrodiesel fuel. Tests using the high-frequency reciprocating rig (HFRR) lubricity tester have now shown that compounds with carboxylic acid moieties or several hydroxy groups such as monoacylglycerols (monoglycerides) possess excellent lubricity. Thus lubricity of fatty compounds depends strongly on structure. These materials, considered contaminants in biodiesel arising often during its production, are lubricity-imparting species in biodiesel. This paper discusses such recent results related to the lubricity of fatty compounds and biodiesel.
