Low Temperature Limits for Gas Turbine Engine Oils

Viscosity and low temperature lubricant characteristics determine turbine engine starting capability, and lubricant motion with respect to the contact surfaces at low ambient temperature. Such low ambient temperatures influence the oil viscosity and also the variation of its curve shape versus the temperature. According to the aforementioned research method, the requirements for accuracy and reliability increase for predicting the work of contact surfaces (bearings) over a wide range of speeds, temperatures and loads. The purpose of this proposal consists of a complex study of physical and mechanical processes between the gas turbine engine oil lubricating system (oil pump, oil filter, oil pipe, and engine rotor bearings) and tribological oil parameters. These parameters include oil viscosity at low ambient temperature [–40 0F], shear stress, shear rate, friction coefficient, and oil film thickness. They will be used to develop a modeling tool and associated methodology to effectively and accurately determine the maximum allowable viscosity for engine oils. For determining the effectiveness of oil lubricity during the start up period between contact surfaces, and the influence of the low ambient temperature [-40 0F], different gas turbine engine oils will need to be tested under a non-stationary process. This non-stationary process, in particular, start and stop has significant influence on the reliability and longevity of oil pump, oil filter, and bearings under extremely low temperature conditions. Recording tribology parameters (oil viscosity, shear stress, shear rate, oil film thickness, friction coefficient, and wear) in this non stationary process requires a new approach about the classification of lubricants concerning their starting properties, and their allowable viscosity under low temperature conditions.