Submitted to: Society of Tribologists and Lubrication Engineers
Publication Type: Abstract Only
Publication Acceptance Date: 5/24/2001
Publication Date: N/A
Technical Abstract: The last two decades have seen substantial increase in the production of high saturate base oils, mainly API Gr. II and III type. This shift from Gr I type oils obtained through conventional refining is mainly due to strict government and environmental regulations. This has triggered a worldwide production of high performing, high quality basestocks for use in lubricant formulation. These oils are currently produced using the state-of-the art hydrocracking, isodewaxing, hydrofinishing technology resulting in less than 1% aromatics and undetectable amount of sulfur and nitrogen. The removal of polyaromatic compounds along with various heterocyclic structures has resulted in enhanced thermal, oxidative and low temperature viscometric behavior of the base fluid. As the aromatic content reaches the minimum value, various physical, chemical and performance-based properties of base oils are controlled by the abundance and composition of the saturates particularly n-, iso- paraffin and naphthenic molecules. Iso-paraffins and naphthenes typically comprise more than 99% of the saturate concentrate in modern Group II and III oils. Hence, it was observed that the nature and length of branching has a profound effect on the diffusion, viscometric and oxidative properties of these oils. The current study deals with detailed structural assignment of the base oils at the molecular level using quantitative NMR spectroscopy. The effect of structure on diffusion and T1 relaxation time is discussed. Thermo-oxidative behavior is compared using PDSC and thin film micro oxidation technique. The usefulness of statistical approach in predicting physiochemical properties and engine test performance are highlighted.