Carbon dioxide UV laser-induced fluorescence in high-pressure flames

Laser-induced fluorescence (LIF) of carbon dioxide is investigated with excitation between 215 and 255 nm with spectrally resolved detection in 5–40 bar premixed CH4/O2/Ar and CH4/air flat-flames at fuel/air ratios between 0.8 and 1.9. The LIF signal consists of a broad (200–450 nm) continuum with a faint superimposed structure, and this signal is absent in similar H2/O2/Ar flames. There is strong evidence this signal arises from CO2, as the signal variations with excitation wavelength, equivalence ratio and flame temperature all correlate with CO2 absorption cross-sections. The signal is linear with pressure and laser fluence within the investigated ranges.