Enhanced ester (MIL‐PRF‐23699G) gas turbine engine lubricant degradation with VIM VAR M50 bearings

Abstract

AbstractPolyol‐ester lubricants have been used and developed for aviation gas turbine engines for many decades. The newest MIL‐PRF‐23699 lubricant class, called enhanced ester (EE), provides the best combination of thermal stability, load carrying capability, boundary lubrication and compatibility with fluoroelastomer O‐rings. Two candidate EE Class formulations and one high thermal stability class formulation conforming to MIL‐PRF‐23699G were evaluated for oil degradation with up to 3000 h of bearing operation. Lubricant degradation was studied using VIM VAR M50 bearings with M50 and silicon nitride balls under two operating conditions using two bearing test rigs. Oil degradation in terms of oxidation time, total acid number and viscosity was studied as a function of time with varying results for the three lubricants.