Two-dimensional temperature field measurements using a molecular filter based technique

Filtered Rayleigh Scattering (FRS) has been investigated to determine the feasibility of the technique to obtain instantaneous two-dimensional temperature measurements in reacting flows. The laser frequency, of an injection seeded Nd:YAG laser, is tuned to an absorption line of iodine which is contained in an optical cell. The iodine filter is placed in front of an intensified CCD camera recording the scattered light. Background scattering from solid surfaces and particles is strongly absorbed by the iodine, while much of the Doppler broadened Rayleigh scattering is transmitted by the filter. The gas temperature can then be deduced from the measured transmission of the molecular Rayleigh scattering. Two different premixed flames were investigated, a hydrogen-air flame created using a Hencken burner and a methane-air flame. The accuracy of the FRS measurements was investigated by comparing FRS-derived temperatures with calculated values and temperatures recorded with coherent anti-Stokes Raman spectroscopy. For the hydrogen-air flames, the FRS method gave temperatures within 2% of the expected value (from measurement and/or calculation). Methane-air flames were investigated to demonstrate the effectiveness of FRS to measure temperatures near surfaces (within 300 μm) and to obtain "large field" two-dimensional temperature information in a buoyantly driven flame. A detailed uncertainty analyses is provided to show the strengths and limitations of the FRS technique for temperature measurements in reacting flows.