Simultaneous Two-Dimensional Visualization of Soot and OH in Flames Using Laser-Induced Fluorescence

Abstract

Two-dimensional visualization of soot has been realized in flames with the use of laser-induced fluorescence in C₂ from laser-vaporized soot [LIF(C₂)LVS]. Soot particles are heated to vaporization temperatures by the absorption of laser radiation. C₂ radicals produced by this process are excited at wavelengths around 563 nm through the transition v’ = 0 d³Π_g ← v” = 1 a³Π_u, and the subsequent fluorescence at ∼516 nm is detected. By frequency-doubling of the laser radiation, wavelengths around 281.5 nm are achieved, which can excite OH radicals to the v’ = 1 A²∑⁺ state from v” = 0 X²Π, with subsequent fluorescence at ∼310 nm. With the use of both these excitation wavelengths, and a Cassegrainian split-mirror telescope as the imaging detection system in front of the charge-coupled device (CCD) camera, simultaneous two-dimensional single-shot images of soot and OH were obtained on a single CCD chip, thus enabling both sooting regions and reaction zones in flames to be monitored.