A quantitative characterization and calibration technique for high-temperature aerosol phosphor thermometry

Worley, C. A Quantitative Characterization and Calibration Technique for High-Temperature Aerosol Phosphor Thermometry. University of Wisconsin-Madison, 2023.

This work characterizes two thermographic phosphors, Eu:BAM and Ce:LuAG, at internal combustion engine relevant temperatures. The characterizations focused on determining the laser-induced luminescence dependence on temperature.

To develop the temperature calibrations, Eu:BAM and Ce:LuAG were introduced separately into an aerosol jet that was heated up to 1100 K. Both scattering and luminescence signals were collected to enable calibration of a scattering referenced aerosol phosphor thermometry (SRAPT) technique. SRAPT ratio values were calculated at the zero seeding density case, allowing for future ease of use for in-cylinder measurements where seeding densities will likely fluctuate. In addition to the temperature calibration, precision parameters, such as fractional sensitivity and single-shot temperature precision index, were determined for each phosphor. For Eu:BAM, the best measured single-shot precision of 20 K occurred at 800 K, with an average precision of 25 K between 700 K – 1000 K. Meanwhile, Ce:LuAG had its best single-shot precision of 16 K at 800 K, with an average precision of 20 K between 700 K to 1000 K. For future in-cylinder turbulent jet ignition measurements, it is suggested that Ce:LuAG be used with a seeding density of approximately 600 mm−3 for phosphor particles with a diameter of approximately 1 µm. This selection will optimize the single-shot temperature precision for the experiments.

In addition to the SRAPT calibration, Eu:BAM was characterized in a tube furnace. While previous bulk powder furnace calibrations have been discredited for APT usage, this attempt mimicked aerosol seeding densities within the furnace. This technique is advantageous compared to aerosol jet calibrations due to the ease of obtaining accurate well-controlled temperatures > 1000 K in furnaces. While a promising technique for rapid calibrations to estimate a new phosphor’s possibilities, this approach should not entirely replace aerosol calibrations due to some differences observed between the current approach and the aerosol measurements in a heated jet.