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

Thermographic phosphors (TPs) exhibit a temperature sensitive emission spectrum when excited with ultraviolet radiation. In this study, 14 μm diameter SiC fibers are coated with ZnO or Dy:YAG using a ceramic binder to a total diameter of 70 ± 9 μm. ZnO and Dy:YAG fibers were used to measure fiber temperatures in the range of 294-450 K and 450-1245 K, respectively. The coated fiber provides higher signal levels compared to TP particle seeding and is no more invasive than the commonly used thermocouple. A calibration is performed to relate fiber temperature to the ratio of luminescent signal collected within two different bands of the fiber emission spectrum. Temperature was measured along the inlet of a series of nitrogen diluted ethylene diffusion flames stabilized on the Yale coflow burner to determine suitable thermal boundary conditions for computational modeling. The boundary condition temperatures were derived from a spline fitting of data acquired from the two fiber types in order to obtain fiber temperature sensitivity from 294 to 1245 K. The peak near-burner temperature was found to be higher than ambient conditions and to increase and shift its location radially outward with increased fuel percentage.