Measurements of turbine blade temperature in an operating aero engine using thermographic phosphors

Abstract

A diagnostic method is introduced for non-contact temperature measurements on the surface of a rotating turbine blade in an operating engine using laser-induced excitation of thermographic phosphor coatings on the blades. Temperature measurements of between 513 °C and 767 °C are demonstrated on a pair of moving turbine blades with a fiber optic probe mounted in the engine at rotational speeds of between 28 000 and 32 750 RPM. The method involves measuring the decay times of laser-induced luminescence from two thermographic phosphors applied to thermal barrier coatings on the turbine blades, one with a short, temperature-sensitive, decay time and the other with a longer, less temperature-sensitive decay time. The phosphors are excited by laser pulses at a wavelength of 355 nm and luminescence is collected at 456 nm from one phosphor and at 485 nm from the other. The effects of motion on the temperature determination are removed by using a ratio of luminescence intensities of the two phosphors. Potential interferences from chemiluminescence, particles, hot surfaces, and reflections within the engine are avoided by limiting the detection to a narrow spectral window around the luminescence wavelengths. The data exhibit high signal-to-noise ratios and the measured temperatures are within the expected range for this engine.