A Brief Analysis of the Development of Aeroengine Lubricants
Release time:
2022-10-29
Author:
Goncord Oil
To ensure the reliable, safe, and efficient operation of aircraft engines while reducing maintenance costs, engine lubrication systems and lubricants have also undergone significant advancements in response to a wide range of challenges.
To ensure the reliable, safe, and efficient operation of aircraft engines while reducing maintenance costs, engine lubrication systems and lubricants have also undergone significant advancements in response to a wide range of challenges.
The lubrication system and lubricating oil of an aircraft engine primarily provide lubrication, cooling, cleaning, and corrosion protection for components such as bearings and the accessory gearbox. They also serve to dampen engine vibrations. The engine’s bearings support the compressor and turbine, while the accessory gearbox drives the hydraulic pump, fuel pump, and starter‑generator—critical systems for the aircraft. This underscores the vital importance of lubricating oil to both the aircraft and its engine.
Lubricating oil is stored in the oil tank. During engine operation, the oil pump maintains continuous pressure, pumping the lubricant through the supply lines to the bearing cavities and to the accessory gearbox and its drive mechanisms. Medium- and large‑size aircraft engines typically employ pneumatic seals to seal the bearing cavities; consequently, the return line from these cavities discharges an aerosol‑like mixture of oil and air. The rotor bearings upstream of the combustion chamber (in the compressor section) operate at lower temperatures than those downstream of the combustion chamber (in the turbine section), resulting in a temperature differential of up to 100°C within these bearing cavities. After performing its lubrication function, the oil–air mixture and the oil discharged from the accessory gearbox are pumped to heat exchangers for cooling, followed by oil–air separation, and finally returned to the oil tank to begin the next cycle. The lubrication system can complete up to three cycles per minute. Upon engine shutdown, the oil pump ceases operation, and the heat contained in the lubricant can no longer be actively dissipated; instead, it must rely on natural cooling, thereby increasing the risk of oxidation and carbonization.
Lubricating components of various types at different temperatures—ranging from bearings to gears; experiencing continuous fluctuations in lubricant temperature within the circulation system; operating for most of the time in the presence of hot air; and coming into contact with diverse materials, including metals and elastomeric seals. These characteristics impose stringent requirements on the lubricant’s thermal stability, oxidation resistance, compatibility, and load-carrying capacity.
After decades of development and accumulation, high‑thermal‑stability and high‑performance specifications—represented by U.S. military standards MIL‑PRF‑23699G and SAE AS5780D—have been established to address oil coking and enhance the compatibility of elastomeric seals. By improving these two critical attributes of engine lubricants, engines can operate more safely and efficiently, reduce unnecessary maintenance, and lower operating costs. Consequently, it is an inevitable trend for users to adopt high‑thermal‑stability or high‑performance lubricants in the future.
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