In order to increase efficiency, modern propulsion systems are required to operate at significantly higher temperatures than in the past. An increased heat load is therefore placed on the fuel that is used as a coolant and on the engine lubrication system. Lubricating oils are typically limited to working temperatures below about 400F. Oil deoxygenation presents an attractive option for significantly increasing this temperature limit. We propose to develop a novel system that will be capable of deoxygenating inline the complete lubricating oil flow for a typical modern military aircraft. The proposed system will use a fixed volume of recycled, essentially oxygen free nitrogen gas to remove the dissolved oxygen from the oil within a contacting device. The oxygen will then be eliminated chemically from the nitrogen in a catalytic converter so that the gas may be returned to the contactor for repeated oxygen stripping. We will perform tests on various contacting devices and a catalytic converter to demonstrate and characterize the deoxygenation characteristics of MIL spec lubricating oil. We will use these data to make projections of the size, weight and durability for a full-scale deoxygenation system and the dependence of this projection upon the output dissolved oxygen level.
Benefit: Lubricating oil may begin to loose its effectiveness as its temperature is raised to around 400F and oxidation begins to occur. Oil must therefore be maintained below this critical temperature. This imposes a limit on engine operating windows and may require large, heavy heat exchangers to cool the oil. By removing the dissolved oxygen from the lubricating oil it is anticipated that its maximum operating temperature may be substantially increased. This will be beneficial to both the engine designer and operator as follows: 1) The designer may save weight, as the lubricating oil will require a smaller, lighter heat exchanger to transfer heat away to the air or fuel cooling fluid. 2) The designer may increase engine peak cycle temperatures since the oil within the lubrication system can sustain a greater temperature before breakdown occurs. 3) The end user may reduce maintenance cycle frequency as the oil will tend to deteriorate at a decreased rate Both military and civilian designers and end users of both gas turbine and reciprocating power plants may realize these benefits. For the civilian and military aircraft markets, the reduced weight and increased engine temperatures will make oil deoxygenation a very appealing option for increasing aircraft cycle efficiency and power-weight ratios. For larger, ground based and ocean going power systems, size and weight may not be such a concern. However, deoxygenation will inevitably present significant potential savings of maintenance costs arising from reduced system down time, labor costs and oil usage. BENEFITS OVER OTHER TECHNOLOGIES We are not aware of other commercial or experimental technologies being developed for deoxygenation of lubricating oil. Efforts have been made to perform online deoxygenation of jet fuel using membrane technology. However, membranes are typically large, heavy, fragile and prone to fouling. They also require a continuous high flow rate of oxygen free gas that must be supplied from engine compressor bleed. This requires a gas-gas heat exchanger and additional mechanical components. We have conducted experiments concerning the deoxygenation of jet fuel using a fuel-gas contactor system. However the device used for that work is unsuitable for much thicker lubricating oil.
Keywords: Oil, De-Oxygenation, Thermal Stability, Lube Oil, Catalyst, Gas Turbine
