Comparison of Three Schemes of Two-Photon Laser-Induced Fluorescence for CO Detection in Flames.

Two-photon excitation laser-induced fluorescence of carbon monoxide suffers from interference from mainly C and strong pressure quenching. This paper presents an investigation of three excitation/detection schemes for two-photon excitation laser-induced fluorescence on carbon monoxide. The schemes are evaluated for pressure and quenching partner dependencies and C interference. Three different emission bands lie in the Hopefield-Birge system: The Ångström BΣ→AΠ band, with two-photon excitation through BΣ←XΠ around 230 nm; the Herzberg band CΣ→AΠ, with two-photon excitation through, CΣ←XΠ, around 217 nm; and the third positive group bΣ→aΠ, also with excitation of BΣ←XΠ around 230 nm. The measurements are performed in laminar premixed flames with various equivalence ratios as well as in a high-pressure cell, where pressure and species concentrations are varied in order to investigate the fluorescence quenching dependence