Dual‐pump CARS measurements of N₂, H₂ and CO in a partially premixed flame

A three‐laser, dual‐pump coherent anti‐Stokes Raman scattering (CARS) technique for the simultaneous detection of nitrogen, carbon monoxide and hydrogen has been developed and tested. Hydrogen Q‐branch lines were used for the determination of relative hydrogen concentrations, which offers a much wider range of detectivity in contrast to approaches in which S‐branch transitions are used. Consequently, hydrogen concentrations could be measured over a whole range of temperatures, from room air to a flame. Measurements were taken in a heated cell and in a partially premixed propane/air flame. Measurements in the cell were in good agreement with theoretical spectral calculations. From measurements in the flame, the relative concentrations of hydrogen and carbon monoxide, which were generated as intermediate species, could be determined. Furthermore, diffusion effects of hydrogen could be observed with the presented approach.