Measuring the temperature of a flame propagating through a quartz tube using high speed colour imaging and thin sic filament based two colour method

Abstract

Blackbody radiation from a thin filament of SiC can be applied to measure hot gases temperature. The technique, Thin-Filament Pyrometer(TFP), exhibits fast temporal response and high spatial resolution owing to the very fine diameter and low heat conductivity. The advantage of this approach is the low cost and simplicity, and it is applicable to the situations where other approaches are difficult to apply. In this study, the investigation of methane-air flame propagating through a tube of a 20mm internal diameter quartz tube with open ends has been carried out. SiC fibres were installed at both ends and the midsection of the tube as radiation emitters. The required volume of methane at each equivalence ratio was measured and injected into the rig and the mixture was ignited at one end (left). The propagating flame was recorded using two high-speed cameras at a frame rate of 2000 fps with one tracking the speed of the flame and another capturing the images of the glowing filament. The images of the glowing filament were then processed to determine the surrounding gas temperature using the two-colour technique. Unlike the two-colour technique using beam splitting and narrow bandpass filtering approach, which often results in misalignment between two grey level images, complicated configuration and high cost, the current technique uses the camera built-in colour-banded filter. The ratio between two of the RGB primary channels was used for the calculation of the temperature. The maximum speed and temperature were observed at equivalence ratio 1.1 with a bell-shaped curve. For cases where the flames were subjected to instabilities, the temperatures were found to fluctuate accordingly. The accuracy of TFP measurement was verified by a commercial Infra-pyrometer.