Simultaneous temperature and relative oxygen and methane concentration measurements in a partially premixed sooting flame using a novel CARS-technique

Using combined 'smeared' vibrational coherent anti-Stokes Raman spectroscopy (VCARS) and dual-broadband rotational CARS (DBB-RCARS) simultaneous measurements of temperature and relative concentrations of O-2/N-2 and CH4/N-2 have been conducted in a fuel-rich (phi = 10), laminar, partially premixed CH4/air-flame. The equivalence ratio was calculated from the relative concentration data determined. Using a dye laser which has been tuned to the Q-branch transitions of methane both WARS and DBB-CARS signals were generated and detected simultaneously by a conventional DBB-RCARS-setup and a planar BOXCARS phase-matching scheme. In contrast to previous approaches, an important advantage of this technique is that no modification of the experimental setup is necessary which would increase the complexity of the system. Due to its molecular symmetry. methane can only be observed by VCARS. The DBB-RCARS approach was used to probe nitrogen and oxygen. In this way the measured signal is separated into two parts. The relative intensity of the 'smeared' WARS signal determines the relative concentration of methane and-the residual DBB-RCARS signal is evaluated by a conventional contour fit to obtain the temperature and the relative concentration of oxygen. Radial temperature and concentration profiles are measured at different downstream positions in the flame. A comparison of the obtained temperatures with previous results from spontaneous Raman scattering and filtered Rayleigh scattering indicates good agreement. (C) 2003 Elsevier B.V. All rights reserved.