Ultrafast Coherent Stokes Raman Scattering of CH4 and CO2 for Simultaneous Measurement of Fuel and Flame Temperature

A three-beam ultrafast coherent Stokes Raman scattering (CSRS) system is demonstrated for simultaneous measurement of the Q-branch of the v1 and 2v2 modes of CO2 and the v2 mode of CH4. Time-domain spectroscopic models were developed for both CO2 and CH4 and a fitting algorithm was constructed to extract CO2 temperature and CH4 temperature separately from the same CSRS spectrum. The CSRS system was applied at various locations in a CH4/air co-flow diffusion flame (Yale Burner). Measured spectra contained transitions belonging to O2 and H2 in addition to those from CH4 and CO2. Mean local temperature measurements spanned from fuel-temperatures of 340 K to flame-temperatures above 2000 K and single-shot precision was analyzed across the measured range. This work successfully demonstrated the ability to collect instantaneous fuel and flame temperatures simultaneously in a non-premixed CH4/air flame using a single CSRS diagnostic configuration.