Vapor Phase Lubrication for Expendable Gas Turbine Engines

Vapor phase lubrication (VPL) is an emerging technology that is currently targeted for application in limited life, expendable engines. It has the potential to cut 90 percent of the cost and weight of the lubrication system, when compared to a conventional liquid lubricated system. VPL, is effective at much higher temperatures than conventional liquid lubrication (600°C versus 200°C), so considerably less cooling for the bearing is required, to the extent that the bearing materials often dictate the maximum upper temperature for its use. The hot no. 8 bearing and the cold no. 1 bearing of the T63 engine were used to evaluate the applicability of this technology to the expendable engine environment. The no. 8 bearing was a custom made hybrid with T15 steel races, silicon nitride balls, and a carbon–carbon composite cage; it was run for 10.7 h at a race temperature of 450°C at full power, without incident. Prior to engine tests, a bearing rig test of the no. 8 bearing demonstrated an 18.6 h life at a race temperature of 500°C at engine full power speed of 50,000 rpm. Cold bearing performance was tested with the standard no. 1 bearing, which consisted of 52100 steel races and balls, and a bronze cage; it was run for 7.5 h at a race temperature of 34°C at flight idle power, without incident. A self-contained lubricant misting system, running off compressor bleed air, provided lubricant at flow rates of 7–25 ml/h, depending on engine operating conditions. These tests have demonstrated for the first time that a single self-contained VPL system can provide adequate lubrication to both the hot and cold bearings for the required life of an expendable cruise missile engine. [S0742-4795(00)01302-2]