Recent developments of thin-filament pyrometry

Thin-Filament Pyrometry (TFP) has been proven to be a useful approach to measure flame temperature. It involves placing a SiC fiber in hot gases and correlating the radiance of the glowing fiber to a calibrated temperature reference. The TFP approach offers simplicity and low cost, and it is useful in situations where other techniques are difficult to apply, such as highpressure environments. In this paper, some recent developments of TFP are discussed. The accuracy of radiation correction, a procedure that is necessary for all TFP measurements, was evaluated by comparing thermocouple derived gas temperature and gas temperature measured by laser techniques (CARS and Raman/Rayleigh scattering) at the same position above a laminar flat premixed CH4/air calibration flame. The aging behavior (emissivity changing with time) that could affect the accuracy of TFP measurements was studied by examining the fiber spectral signal over hours at high temperature. Two TFP approaches were tested and discussed. The first approach utilizes one narrowband interference filter and relies only on a calibration at one temperature. Other temperatures can be inferred according to Planck's law as long as the material is stable (no significant aging effect) and the optical setup is kept unchanged. This approach avoids the need for spectral characterization of the detector and knowledge of the emissivity model of the fiber. The second approach based on color-ratio principles was applied to yield simpler and more robust measurements. It relies on the fiber greybody assumption and camera spectral response characterization, but is free of temperature calibration.