Multiple species coherent anti-stokes Raman spectroscopy (CARS) in turbulent jet flames

Several multi-color CARS approaches have been recently demonstrated. One of these approaches, dual-Stokes CARS, is a straight-forward addition of two single-color CARS processes. This approach has been used to take simultaneous single-pulse measurements of temperature and the mass fractions of N2, CO, O2 and CO2 in turbulent nonpremixed jet flames of CO/N2. The simultaneous measurement of all major species allows the nonresonant susceptibility of the mixture to be calculated directly rather than assumed, thus eliminating a potential source of error in the measurements. The measurement of all major species also allows calculation of the mixture fraction, defined as the local mass fraction of fluid originating from the primary stream. Direct measurement of the mixture fraction is very useful as it is necessary for the accurate modeling of turbulent reacting flows. The accuracy of the BYU dual-Stokes CARS instrument has been determined by performing calibration measurements over flat flames of CO/N2 of known composition. This has shown that measurement of four species using CARS is possible and sufficiently accurate to justify use of the technique in the characterization of turbulent flames. Measurements were then taken in turbulent nonpremixed jet flames of the same fuel, which directly demonstrate the applicability of the instrument to turbulent reacting flows. A sample of data from more extensive measurements in turbulent nonpremixed jet flames is also given to show the extent to which multiple species CARS has been employed.