Phosphor thermometry for high temperature gas turbine applications

Abstract

In the paper developments and some preliminary experiments concerning the application of thermographic phosphors for surface temperature and heat flux measurements in gas turbine combustion chambers are presented. When illuminated with W light (typically from a pulsed laser) these material exhibits phosphorescence, which is temperature dependent by Virtue of variations in the relative intensity of distinct emission lines or of variations in the time constant of the exponential emission decay which occurs once excitation has ceased. Both modes of sensitivity have been investigated with a range of phosphors including are YAG-:%, YAG:Dy and Y203:Eu. Of these YAG:Dy has been shown to be best suited to measurements in combustion chambers. It is sensitive to temperatures in the range 300 to 1500% emits light in the blue green region of the spectrum where blackbody radiation is relatively weak and exhibits both modes of sensitivity.In addition a number of techniques for laying down phosphor coatings on metal substrates are reviewed and an experimental investigation of two techniques is presented. Firstly, the use of chemical binders similar to those used in thermal paints and, secondly, a new cost effective coating technique refmed to as Electrostatic assisted Combustion Chemical Vapour Deposition (EACVD) which has been developed in the Materials Department at Imperial College. The latter allows thin layers of phosphors to be laid down without the need for a chemical binder and with close control of coating composition and thickness. To demonstrate the technique a 2pm thick layer of Y203:Eu has been laid down on a nimonic substrate and a performance comparison made with a similar coating laid down using the alternative chemical binder technique. The EACVD coating has been shown to be more robust than those laid down with chemical binders whilst the coating shows similar temperature sensitivity.

An analysis of Y2O3:Eu3+ thin films for thermographic phosphor applications

“…The photoluminescence properties of the thin luminescent films were measured using a 190 mm focal length corrected cross 2 Czerny-Turner monochromator 5 with a 254 nm wavelength of a 4 W mercury hand lamp. The spectrum was collected with an attached thermoelectrically cooled (down to À30 1C) 1024 Â 128 pixel charged-couple device located at the exit slit of the spectrometer.…”

“…While thermistors can be deposited onto a component to give accurate temperature measurements; again, the challenge of a physical connection needs to be overcome. These devices can impede the operation of the engine and when in operation over long periods of time, the stresses induced on these devices can lead to their eventual failure [2,4]. Therefore, non-contact and non-intrusive techniques are under constant development.…”

“…To design a more fuel-efficient engine for aircraft or energy generation, determining the temperature of the internal components during operation is a critical measurement in evaluating the efficiency of the engine. Conventional techniques such as pyrometry, thermocouples, or thermistors, can only provide a limited amount of reliability, reproducibility and accuracy for measuring temperature under these conditions [1][2][3][4][5]. The problem that all these conventional techniques have in common is that they can only measure the temperature in one spot.…”

Phosphorescent thermal history sensors

“…Reversible changes in thermographic phosphors have been used for many years to measure surface temperatures or heat fluxes under conditions relevant to gas turbines [12][13][14][15][16][17][18]. There are, however, temperature driven processes associated with phosphors that lead to irreversible changes in their emission characteristics.…”

Temperature Sensing inside Thermal Barrier Coatings using Phosphor Thermometry

“…Calibration of the life time decay against temperature was performed placing the sample into an optically accessible furnace [22]. When the sample was into the furnace, the temperature was set to the maximum value of interest (950°C in this case) and then the furnace was switched off.…”