Triple-pump coherent anti-Stokes Raman scattering (CARS): temperature and multiple-species concentration measurements in reacting flows

Abstract

Two types of triple-pump coherent anti-Stokes Raman scattering (CARS) systems for the simultaneous measurement of temperature and multiple-species concentrations are presented. In the first system, the ro-vibrational transitions of N 2, O 2, and H 2 are probed using three narrowband pump beams and a broadband Stokes beam. In the second system, pure rotational transitions of N 2/O 2 and the ro-vibrational transitions of N 2/CO 2 are probed using two narrowband pump beams, a broadband pump beam, and a broadband Stokes beam. The use of a broadband pump source in the second CARS system allows rotational and ro-vibrational transitions of different molecules to be probed simultaneously. For both CARS systems, the signals appear at two distinct wavelengths. The CARS signals at the two wavelengths are separated by dichroic mirrors before being detected by two spectrometer-CCD detection systems. For proof-of-concept demonstrations, single-shot and averaged measurements are performed in an atmospheric-pressure hydrogen–air diffusion flame and in a carbon dioxide-seeded, near-adiabatic hydrogen–air flame stabilized over a Hencken burner. These are, to our knowledge, the first reported experiments of triple-pump coherent anti-Stokes Raman scattering for the simultaneous measurement of temperature and multiple-species concentrations.