Novel Method for Evaluating the Aging of Aviation Turbine Engine Oils via High-Temperature Bearing Deposit Tests

Aviation turbine engine oils require excellent thermal-oxidative stability because of their high-temperature environments. High-temperature bearing deposit testing is a mandatory method for measuring the thermal-oxidative performance of aviation lubricant oils, and the relevant apparatus was improved in the present study. Two different commercial aviation turbine engine oils were tested, one with standard performance (known as the SL oil) and the other with high thermal stability, and their thermal-oxidative stability characteristics were evaluated. After 100 h of high-temperature bearing testing, the SL oil was analyzed by using various analytical techniques to investigate its thermal-oxidative process in the bearing test, with its thermal-oxidative degradation mechanism also being discussed. The results indicate that the developed high-temperature bearing apparatus easily meets the test requirements of method 3410.1 in standard FED-STD-791D. The viscosity and total acid number (TAN) of the SL oil increased with the bearing test time, and various deposits were produced in the bearing test, with the micro-particles of the carbon deposits being sphere-like, rod-like, and sheetlike in appearance. The antioxidant additives in the oil were consumed very rapidly in the first 30 h of the bearing test, with N-phenyl-1-naphthylamine being consumed faster than dioctyldiphenylamine. Overall, the oil thermal-oxidative process involves very complex physical and chemical mechanisms.