Full-spectrum fitting method applied to YAG:Dy : Impact of oxygen content and laser fluence on wall-temperature phosphor thermometry for combustion

Abstract

Achieving the European net-zero greenhouse gas emissions target requires the development of sustainable combustion processes across various industrial sectors. These promising alternatives introduce new challenges, such as modifying wall heat transfer. Accurate surface temperature measurements are essential for understanding these effects. Laser-Induced Phosphorescence (LIP) provides a semi-invasive method that exploits the temperature-dependent phosphorescence spectra of thermographic phosphors. YAG:Dy is a thermographic phosphor that emits a phosphorescence signal over the range of 300 K to 2000 K. However, its poor sensitivity with the intensity ratio method and its low sensitivity at lower temperatures with the lifetime method limit its use to high-temperature combustion applications. Additionally, its sensitivity to ambient oxygen reduces the accuracy of those methods. This study evaluates the performance of the Full-Spectrum Fitting (FSF) method, developed by the EM2C Laboratory in Lechner et al. (2022), when applied to YAG:Dy. The method leverages the phosphor’s spectral temperature dependence over a wide range (303 to 1773 K), achieving an accuracy of 0.3 K and a precision of 8.4 K under given experimental conditions. It is observed that there is a laser fluence threshold above which temperature determination using the FSF method becomes independent of laser fluence. The impact of YAG:Dy’s sensitivity to oxygen concentration on temperature measurement is quantified. In the worst case, uncertainty in oxygen concentration can introduce a temperature error ranging from 7 to 19 K. Guidelines are provided to help mitigate these sensitivities in combustion applications.