QUANTITATIVE MEASUREMENTS OF CO CONCENTRATIONS IN LAMINAR AND TURBULENT FLAMES USING TWO-PHOTON LASER-INDUCED FLUORESCENCE

摘要

Laser diagnostics can provide nonintrusive measurements of the instantaneous velocities and species concentrations, and statistical information from such measurements may be used to evaluate modeling approaches for turbulent nonpremixed combustion. An important flame constituent in these studies is carbon monoxide. Numerous studies have been performed in turbulent flames using single-shot Raman scattering measurements, despite extremely small optical scattering cross sections, which require the use of high-energy laser pulses. In the presence of hydrocarbons, high-energy laser pulses cause interfering light, for instance from emission due to laser-produced C{sub}2. In this study, we examine concentration measurements of CO using two-photon, laser-induced fluorescence (TPLIF). Excitation of the X{sup}1Σ{sup}+ -^sB{sup}1Σ{sup}+ transition of CO is attempted because laser photons can also photoionize the excited state. The photoionization rate can help make TPLIF detection of CO quantitative. This is examined in several laminar and turbulent flames by direct comparison with simultaneous Raman measurements of CO concentration. Excellent agreement is observed for a number of laminar flame conditions. Disappointing results are obtained in turbulent CO/H{sub}2/N{sub}2 jet flames. Reasons for the anomalous results are explored.