Raman-scattering gas temperature measurements in particle-laden flows

The feasibility of making time-averaged Raman-scattering temperature measurements in highly luminous flows was investigated in tests on the Sandia Atmospheric Combustor Exhaust Simulator facility. The diluted exhaust stream from a methane-burning combustor was seeded with 5 micrometer diameter fly ash particles. Test temperatures ranged from 900 K to 1450 K at particle densities up to 6000 particles/cc. A pulsed argon-ion probe laser and a gated detection system for enhancement of signal-to-background ratio were used. Scans of the Stokes Q-branch vibrational Raman spectrum of nitrogen were fit by calculated spectra to determine temperature. The Raman-scattered signal was small but measurable in all cases. There was no apparent laser-induced interference from either fluorescence or particle incandescence. Good agreement between Raman-scattering temperature measurements and radiation corrected thermocouple measurements was obtained.