Intracavity laser absorption spectroscopy of sooting acetylene/air flames

Intracavity laser absorption spectroscopy (ICLAS) is used to measure the absolute concentration profiles of HCO and C 2 in low-pressure acetylene/oxygen/nitrogen flames with equivalence ratios ϕ=0.8, 1.0, 1.5, 2.0 and 2.5. The flames with ϕ=2.0 and 2.5 are soot-producing, with light extinction reaching 0.1% per pass in the flame with ϕ=2.5. This strong broadband extinction does not affect the sensitivity of ICLAS, however. The temperature profiles of the flames were measured using laser-induced fluorescence of the OH radicals. For C 2 concentration measurements, the (0–2) vibronic transition of the Swan band is used. The lines of this transition are located close to the HCO lines, making it possible to measure the two radical concentrations simultaneously. The C 2 concentration is highest in the ϕ=1.5 flame, and lower in the lean and heavily sooted ϕ=2.5 flames.