Fluorescence quantum yield of carbon dioxide for quantitative UV laser-induced fluorescence in high-pressure flames

摘要

The fluorescence quantum yield for ultraviolet laser-induced fluorescence of CO_2 is determined for selected excitation wavelengths in the range 215-250 nm. Wavelength-resolved laser-induced fluorescence (LIF) spectra of CO_2, NO, and O_2 are measured in the burned gases of a laminar CH_4/air flame (φ = 0.9 and 1.1) at 20 bar with additional NO seeded into the flow. The fluorescence spectra are fit to determine the relative contribution of the three species to infer an estimate of fluorescence quantum yield for CO_2 that ranges from 2-8 × 10~(-6) depending on temperature and excitation wavelength with an estimated uncertainty of ±0.5 × 10~(-6). The CO_2 fluorescence signal increases linearly with gas pressure for flames with constant CO_2 mole fraction for the 10 to 60 bar range, indicating that collisional quenching is not an important contributor to the CO_2 fluorescence quantum yield. Spectral simulation calculations are used to choose two wavelengths for excitation of CO_2, 239.34 and 242.14 nm, which minimize interference fromrnLIF of NO and O_2. Quantitative LIF images of CO_2 are demonstrated using these two excitation wavelengths and the measured fluorescence quantum yield.