CARS thermometry in a 2-m-diameter methanol pool fire

We report what is believed to be the first application of coherent anti-Stokes Raman scattering (CARS) to full-scale fire testing. A CARS instrument has been constructed at the newly commissioned FLAME (Fire Laboratory for Accreditation of Models and Experiments) facility at Sandia, where the CARS system has been used for thermometry in 2-m-diameter, turbulent methanol pool fires. Fielding of CARS in such a large-scale facility presents several challenges, including long-distance propagation of laser beams, shielding of optics from intense heat, the impact of beam steering and fiber-optic coupling of the CARS signal to remotely located detection equipment. The details of a CARS instrument that meets these challenges are presented, along with the construction of the unique new FLAME facility itself, which has been designed to accommodate optical and laser-based diagnostics to full-scale fire experimentation. The performance of the CARS instrument is investigated in a premixed methane-air flat flame to estimate the precision in single-shot CARS temperatures. Single-shot CARS spectra and best-fit temperatures from a methanol pool fire are presented, and an estimate of the pdf of the temperature fluctuations from the pool-fire environment is obtained.