Dual pump CARS measurements in counter-flow flames using an injection-seeded optical parametric pump source
Abstract
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). For the N2 molecule, Raman transitions near 2300 cm-1 were excited using 532-nm pump beam and Stokes beam at 607 nm; while the probe beam at 560 nm was scattered from the induced polarization to generate CARS signal near 496 nm. For the CO 2 molecule, the pump and probe beams were reversed, with the CARS signal produced at the same wavelength. 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. Folded BOXCARS phase-matching was implemented. 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 CH4/O2/N2 partially premixed and non-premixed flames and a number of H2/O2/N 2 non-premixed flames at atmospheric pressure. The generated CARS signal was dispersed using a 0.5-m spectrometer and was detected using an imaging camera. Sandia CARSFT code was used to conduct a least squares fit process comparing the square-root of the background-corrected normalized CARS signal with theoretical calculations. Temperature was obtained from fitting only the nitrogen spectrum at every measurement location. Knowing the temperature and N2 mole fraction values, CO2 mole fractions were determined by conducting the least-squares fit on the entire dual-pump CARS spectra. 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. For hydrogen flames, the shape and magnitude of temperature profiles were predicted well; however, there was some discrepancy regarding the spatial location.
Degree
M.S.M.E.
Advisors
Lucht, Purdue University.
Subject Area
Mechanical engineering
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