Lubricant Inerting

The recent development of nitrogen concentrators that can filter a stream of almost pure nitrogen from air now makes it practicable to operate closed lubrication systems in an inert atmosphere to limit lubricant oxidation during use—so called “lubricant inerting.” This paper outlines previous work on this topic and indicates the possible benefits of lubricant inerting using nitrogen concentrators. Two important issues are then explored: whether existing lubricant additives can work effectively in a low oxygen environment and the extent to which inerting extends lubricant life in a tribological system. It is found that friction modifiers and extreme pressure additives work as effectively or better in the absence of oxygen compared to their performance in dry air with 21% oxygen (O₂). Some ashless phosphorus antiwear additives function better when no oxygen is present, some are less effective in nitrogen than in air, and some appear indifferent to the presence or absence of oxygen. High temperature lubricant testing in a tribometer indicates that degradation, as measured by viscosity increase, Fourier-transform infrared spectroscopy (FTIR), and total acid number (TAN), is almost completely suppressed in nitrogen and is greatly reduced when only 2% O₂ is present. The work carried out to date suggests that lubricant inerting has the potential to provide a step-change in lubrication technology, offering greatly extended lubricant lives, enabling much higher operating temperatures, and contributing considerably to sustainability.