A study of thermographic phosphor thermometry in an operating turbofan engine

Abstract

A new method of remote thermometry utilizing the temperature dependent optical properties of thermographic phosphors was evaluated for use in measuring high-pressure turbine blade metal temperatures in an operating turbofan engine test rig. Thermographic phosphors, ceramics doped with a rare earth metal, were bonded to the turbine blades. These phosphors exhibit fluorescence when optically excited by a laser, and both the intensity and the rate of decay of the fluorescence are temperature dependent An optical fiber probe was used to carry the excitation laser light to the blade surface, and to receive the resulting fluorescence. The blades rotated at speeds up to 30,000 rpm. Synchronization was achieved by a digital pattern recognition circuit, capable of locating a specific blade with each revolution. The investigation concentrated on thennographic phosphor characteristics, phosphor binding methods, and probe optical efficiency. Although poor performance of the selected phosphor binding methods impeded the location of the fluorescence signal in the operating gas turbine engine, many operating characteristics of the technique were determined, and the new measurement technique was established as a promising candidate for further research in the temperature measurement of rotating surfaces inside a turbine engine.