On surface temperature measurements with thermographic phosphors: A review

Thermographic phosphors for thermometry: A survey of combustion applications

The temperature dependence of luminescent coatings which measure surface pressure is a well established problem. Temperature correction of the surface pressure measurement is often carried out by incorporating a second luminescent coating or by co-immobilizing a second luminophore to provide a surface temperature profile. This usually complicates the measurement process by requiring a second camera or sophisticated filtering to distinguish between the two luminescent processes. Here, a single-camera, temperature-corrected PSP (pressure-sensitive paint) system was developed. A new oxygen-permeable sol–gel-based paint, containing both a temperature- and a pressure-sensitive luminophore is described. The fluorescence decay times of the two luminophores are separated by several orders of magnitude. This allows pressure- and temperature-dependent luminescent decay measurements to be separated in the time domain. In addition, the two luminophores were selected such that their absorption and emission spectra occur in similar spectral regions. This avoids the need for different excitation sources or detection filters. Hence a single camera with a gated image intensifier can be used to measure the lifetime of each luminophore within the same cycle. Image alignment issues experienced in dual-camera systems are also avoided. This new PSP has the potential to provide a temperature-corrected surface pressure profile using a single excitation source and detection system.

https://iopscience.iop.org/article/10.1088/0957-0233/13/10/307/pdf

Temperature-corrected pressure-sensitive paint measurements using a single camera and a dual-lifetime approach

A method of eliminating pixelization effect from en face optical coherence tomography (OCT) image when a fiber bundle is used as an OCT imaging probe is presented. We have demonstrated that applying a histogram equalization process before performing a weighted-averaged Gaussian smoothing filter to the original lower gray level intensity based image not only removes the structural artifact of the bundle but also enhances the image quality with minimum blurring of object’s image features. The measured contrast-to-noise ratio (CNR) for an image of the US Air Force test target was 14.7dB (4.9dB), after (before) image processing. In addition, by performing the spatial frequency analysis based on two-dimensional discrete Fourier transform (2-D DFT), we were able to observe that the periodic intensity peaks induced by the regularly arrayed structure of the fiber bundle can be efficiently suppressed by 41.0dB for the first nearby side lobe as well as to obtain the precise physical spacing information of the fiber grid. The proposed combined method can also be used as a straight forward image processing tool for any imaging system utilizing fiber bundle as a high-resolution imager.

Pixelation effect removal from fiber bundle probe based optical coherence tomography imaging.

In this study a novel technique for 2D spray temperature measurement is presented. For this purpose the thermographic phosphor (TP) Mg4GeO5.5F:Mn was dispersed in n-dodecane and atomised using a conventional semi solid-cone nozzle. The thermographic phosphor was excited electronically by a frequency tripled Nd:YAG laser (355 nm). An ICCD-camera in combination with an image doubler detected the subsequently emitted phosphorescence at both peak emission wavelengths located at 633 nm and 659 nm, respectively. Utilising suitable calibration measurements, the local spray temperature was determined by evaluating the intensity ratio of both emission wavelengths. To the knowledge of the authors this is the first approach of spray temperature measurement exploiting the temperature dependent intensity ratio of thermographic phosphors.

Spray thermometry using thermographic phosphors

Mapping the surface temperature of ceramic and superalloy turbine engine components using laser-induced fluorescence of thermographic phosphor

An endoscopic imaging system for turbine engine pressure sensitive paint measurements

It is well known that phosphor thermometry may be used in environments characterized by high brightness from blackbody background or combustion flames. The present work describes measurements performed inside an operating turbine engine. For this application, two thermographic phosphors were chosen to cover the expected temperature range. The first, Yttrium Oxide doped with Europium (Y2O3:Eu) has received much attention as a temperature-indicating material for higher temperature ranges. The second, Yttrium Vandidate doped with Thulium (YVO4:Tm) is relatively new, and was chosen for several reasons. First, it exhibits a bright emission line at 475 nm, which is much bluer than Y2O3:Eu line at 611 nm. Blackbody emission will have less effect on the detection of blue emission as opposed to the red. Second, YVO4:Tm also exhibits temperature dependence from at 100 C to above 900 C in the range not covered by Y2O3:Eu. This testing proved that temperature measurements are possible in this environment, given proper selection of the emission wavelength and temperature range.

http://web.ornl.gov/~webworks/cppr/y2001/pres/123382.pdf

Tom Bonsett

Papers

Mapping the surface temperature of ceramic and superalloy turbine engine components using laser-induced fluorescence of thermographic phosphor

An endoscopic imaging system for turbine engine pressure sensitive paint measurements

Phosphor Thermometry in an Operating Turbine Engine