Multiplex CARS for simultaneous measurement of temperature and CO_2 and H_2 concentrations in a combustion environment

Abstract

Simultaneous temperature and CO(2) concentration measurements with multiplex coherent anti-Stokes Raman scattering (CARS) spectra of CO(2) were performed. CARS spectra of pure CO(2) and various mixtures of CO(2) and N(2) in a furnace were recorded at various temperatures to test the computer code that simulates CO(2) CARS spectra using recent spectroscopic constants. The temperatures obtained from the CO(2) CARS spectra were in good agreement with thermocouple temperature measurements. However, the CO(2) concentrations cannot be accurately extracted from these spectra. It is believed by the authors that the cross-coherent effect, which has not been included in the present model, and the difficulty of accurately accounting for the background are two important factors affecting the CO(2) concentration measurements. H(2) pure rotational lines S(4) and S(5) were found in the CO(2) CARS spectra of a hydrocarbon flame. These assignments were confirmed from intensity ratio measurements of S(4) and S(5) lines at different temperatures. A theoretical study shows that the H(2) concentration measurement from the S(5) line should be more sensitive than that of the S(4) and S(9) lines at the flame temperature. CARS spectra of preanalyzed mixtures of N(2), CO(2), and H(2) in a furnace were recorded to investigate the feasibility of inferring the H(2) concentration from these spectra. Simultaneous CO(2) and H(2) multiplex CARS spectra were also recorded in a CH(4)/O(2) diffusion flame and in the MSU/DIAL test stand to observe the high temperature spectra. The results of these measurements are presented.