High Temperature Liquid Lubricant Development Part II: Bench Test Development

High temperature liquid lubricants are essential to the success of the low heat rejection engine under development. Engine tests in Part I of this paper have demonstrated that existing commercial lubricants are totally inadequate to perform under escalated thermal environments. Engine failures occur primarily due to either lubricant degradation, or performance issues related to lubricant degradation. Stability of lubricants must be enhanced. The most important lubricant requirements are oxidative stability and deposit sludge control. Bench tests that correlate with model engine tests are useful tools for lubricant development. Nine oxidation and deposit tests were selected. A database was established to evaluate their capability to correlate with the lubricant as it performed within the engine. Modifications were made to three of these nine tests to explore the possibility of improving correlation. Most oxidation tests are capable of predicting performance of most oils. Severity of these oxidation tests need to be increased to shorten test durations, and to better differentiate the ranking. Deposit characteristics in engine tests are more complicated. Existing deposit tests fail to predict oil performance. A different test is required to correlate with deposits or sludge at each location of an engine. Possible directions of design change for deposit tests are discussed.