Boundary condition thermometry using a thermographic-phosphor-coated thin filament

Area of Science:

• Materials Science
• Combustion Science
• Optical Diagnostics

Background:

• Thermographic phosphors (TPs) are materials with temperature-dependent emission spectra under UV excitation.
• Accurate temperature measurements are crucial for understanding combustion phenomena and validating computational models.
• Existing methods like thermocouple use can be invasive or provide lower signal levels compared to advanced techniques.

Purpose of the Study:

• To develop and calibrate coated silicon carbide (SiC) fibers as thermographic phosphors for high-temperature measurements.
• To measure temperature distributions in ethylene diffusion flames for establishing thermal boundary conditions.
• To assess the feasibility of using coated fibers as a non-invasive thermometry technique in combustion.

Main Methods:

• Coating 14 μm SiC fibers with Zinc Oxide (ZnO) for 294-450 K and Dy:YAG for 450-1245 K.
• Calibrating the luminescent signal ratio against temperature for each fiber type.
• Measuring temperatures along the inlet of nitrogen-diluted ethylene diffusion flames using the coated fibers.

Main Results:

• Coated fibers provided higher signal levels than TP particle seeding and comparable invasiveness to thermocouples.
• A continuous temperature sensitivity from 294 K to 1245 K was achieved by combining ZnO and Dy:YAG data.
• Near-burner peak temperatures were higher than ambient, increasing and shifting radially outward with higher fuel percentages.

Conclusions:

• Coated SiC fibers are effective, non-invasive thermometry tools for combustion research.
• The developed method provides accurate thermal boundary conditions for computational fluid dynamics (CFD) modeling of diffusion flames.
• Flame temperature characteristics are sensitive to fuel concentration, with higher concentrations leading to elevated and radially dispersed peak temperatures.