Molecular filtered Rayleigh scattering applied to combustion

Molecular filtered Rayleigh scattering (FRS), employing an iodine vapour fi lter and an injection-seeded Nd:YAG laser, was utilized to measure instanta neous and average temperature fields in combustion environments. With FRS t hermometry, the vapour within the cell strongly absorbs background scatteri ng from surfaces and particles, while much of the Doppler-broadened Rayleig h scattering is not absorbed by the iodine transition; the gas temperature can then be deduced from the measured transmission of the molecular Rayleig h scattering. For demonstration purposes and to evaluate the accuracy of th e technique, we employed a near-adiabatic hydrogen-air flame. The accuracy of the FRS measurements was investigated by comparing FRS-derived temperatu res with those (1) calculated assuming adiabatic equilibrium conditions and (2) recorded with the CARS (coherent anti-Stokes Raman spectroscopy) techn ique. For the hydrogen-air flames, the FRS method gave temperatures within 2% of the expected value. The FRS thermometry instrument was then applied t o a stagnation-flow, premixed methane-air flame, images recorded here demon strate the utility of the FRS method for temperature imaging, particularly near surfaces. In this flow field, we compared the FRS temperatures with th ose from a one-dimensional model and investigated the radial extent of the uniform temperature region, to assess the assumption of one-dimensionality. In addition, we demonstrated the feasibility of simultaneous measurements of the temperature and velocity fields, the latter derived from the particl e image velocimetry technique.