LAUSR

Abstract Infrared (IR) planar laser-induced fluorescence (LIF/PLIF) exploits the vibrational level transitions of small gas molecules to achieve spatially-resolved spectroscopic information of the species for combustion and flow-field studies. While typical LIF utilizes electronic excitations with ultraviolet or visible lasers, IR LIF presents an alternative for molecules that are not readily accessible with a conventional UV/visible excitation-collection system. In view of the complexities rooting from longer vibrational level lifetimes and more densely-spaced energy levels, a comprehensive vibrational energy transfer model is developed for state-to-state population evolution and transition process characterization, and a typical CO 2 /CO/H 2 O/O 2 /N 2 system relevant to combustion gas mixture is studied by considering a total of 265 energy states and 85,036 transition pathways. The resultant fluorescence signal is thereby studied, with quantitative dependence on local temperature, pressure, gas composition, as well as excitation laser parameters including wavelength, power level and linewidth. Further optimization of collection scheme can be achieved by considering the time-histories and major transition pathways pertaining species evolution on different energy levels. The study develops general modelling and methodology for characterizing the temporal and spectral behavior of a vibrationally-excited molecular system, and demonstrates the potential for quantitative, spatially-resolved diagnostics using IR LIF/PLIF.