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 C2 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 C2 interference. Three different emission bands lie in the Hopefield-Birge system: The Ångström B(1)Σ(+)→A(1)Πu band, with two-photon excitation through B(1)Σ(+)←X(1)Π around 230 nm; the Herzberg band C(1)Σ(+)→A(1)Πu, with two-photon excitation through, C(1)Σ(+)←X(1)Π, around 217 nm; and the third positive group b(3)Σ→a(3)Π, also with excitation of B(1)Σ(+)←X(1)Π 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.