Molecular filtered rayleigh scattering applied to combustion and turbulence

Molecular Filtered Rayleigh Scattering (FRS) has been demonstrated to measure the instantaneous and average temperature field in combustion environments. FRS employs an optical cell placed in front of an intensified CCD camera which records the Rayleigh scattered signal from the flow field illuminated by a sheet of laser light from a Nd: YAG pulsed laser. The laser is tuned to an absorption line of iodine vapor which is contained in the optical cell. This causes background scattering from solid surfaces and particles to be strongly absorbed, while much of the Doppler broadened Rayleigh scattering is transmitted through 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. Methane-air flames were investigated to show the effectiveness of FRS to obtain instantaneous two-dimensional temperature information in a buoyantly driven flame. The FRS thermometry system was then utilized to investigate a stagnation-flow methane/air flame and compare the results with a 1-D model. To enhance the capabilities of FRS, the feasibility of simultaneously measuring the instantaneous velocity field using Particle Image Velocimetry was also demonstrated.