Intensity-ratio and color-ratio thin-filament pyrometry: Uncertainties and accuracy

Thin-filament pyrometry (TFP) has been proven to be a useful approach to measure flame temperature. It involves placing a thin filament (SiC fiber typically) in hot gases and inferring the gas temperature from the radiance of the glowing filament. The TFP approach offers simplicity and low cost, and it is useful in situations where other techniques are difficult to apply, such as high-pressure environments. In this paper, some recent developments of TFP are discussed. The physical backgrounds of two TFP approaches, namely the intensity-ratio approach and the color-ratio approach, are reviewed along with the required radiation correction. Several sources of error, such as the fiber aging behavior (fiber properties varying with time), spectral emissivity and calibration, have been investigated. Measurements in well-calibrated laminar flames show very good agreement with reference temperatures based on N₂ coherent anti-Stokes Raman scattering (CARS) measurements. Uncertainty analysis has also been performed and provides insights on improving TFP measurement accuracy.