Infrared planar laser-induced fluorescence imaging and applications to imaging of carbon monoxide and carbon dioxide

This dissertation introduces infrared planar laser-induced fluorescence (IR PLIF) techniques for visualization of species that lack convenient electronic transitions and are therefore unsuitable for more traditional electronic PLIF measurements. IR PLIF measurements can generate high signal levels that scale linearly with both laser energy and species concentration, thereby demonstrating advantages over Raman and multiphoton PLIF techniques.; IR PLIF is shown to be a straightforward and effective tool for visualization of CO and CO₂ in reactive flows. The slow characteristic times of vibrational relaxation and the large mole fractions of CO and CO₂ in typical flows lead to high IR PLIF signal levels, despite the low emission rates typical of vibrational transitions. Analyses of rotational energy transfer (RET) and vibrational energy transfer (VET) show that excitation schemes in either linear (weak) or saturated (strong) limits may be developed, with the fluorescence collected directly from the laser-excited species or indirectly from bath gases in vibrational resonance with the laser-excited species. Use of short (∼1 μs) exposures (for CO) or short exposures combined with long-pulse, high-pulse-energy excitation (for CO₂) minimizes unwanted signal variation due to spatially-dependent VET rates.; Results are presented for flows ranging from room-temperature mixing to a benchmark CH₄ laminar diffusion flame. Linear excitation is appropriate for CO due to its slow vibrational relaxation. However, linear excitation is not well-suited for CO₂ imaging due to fast H ₂O-enhanced VET processes and the attendant difficulty in interpreting the resulting signal. Saturated excitation using a CO₂ laser (or combined CO₂ laser-OPO) technique is most appropriate for CO ₂, as it generates high signal and minimizes spatial variations in fluorescence quantum yield.; Since IR PLIF is applicable to most IR-active species, it has a high potential for expanding the diagnostic possibilities available to combustion researchers. Such diagnostics might include visualization of the fuel region of lifted flames, CO-formation regions in flames, or exhaust mixing processes in internal combustion engines as applied to residual-induced autoignition.