Dual-Pump CARS Measurements in Counter-Flow Flames using OPO

A new laser system has been developed to measure temperature and major species concentrations using dual-pump N2-CO2 coherent anti-Stokes Raman scattering (CARS). The second harmonic output from an injection-seeded Nd:YAG laser was used as one of the narrowband pump beams.The second narrowband pump beam was generated from an optical parametric oscillator injection-seeded at the idler wavelength using an external cavity diode laser.A broadband dye laser produced the Stokes beam. The three beams were focused between two opposing nozzles of a counter-flow burner facility to measure temperature and major species concentrations in a variety of partially premixed and non-premixed methane and hydrogen flames at atmospheric pressure. Sandia CARSFT code was used to conduct a least squares fit process. Temperature was obtained from fitting only the nitrogen spectrum at every measurement location. In general, excellent agreement was observed between measured temperature profiles and those predicted using an opposed-flow flame code in conjunction with detailed chemistry for methane flames.