SOOT-VISUALIZATION STRATEGIES USING LASER TECHNIQUES - LASER-INDUCED FLUORESCENCE IN C2 FROM LASER-VAPORIZED SOOT AND LASER-INDUCED SOOT INCANDESCENCE

Strategies for spatially resolved soot volume-fraction measurements have been investigated in sooting laboratory flames with known soot characteristics. Two techniques were compared: Laser-Induced Fluorescence in C2 from Laser-Vaporized Soot (LIF(C2)LVS), and Laser-Induced Incandescence of soot (LII). The LII signal is the increased temperature radiation from soot particles which have been heated to temperatures of several thousand degrees as a consequence of absorption of laser radiation. The LIF (C2)LVS technique is based on the production of C2 radicals from laser-vaporized soot which occurs for laser intensities greater-than-or-equal-to 10(7) W/cm2. A laser wavelength is chosen such that besides vaporizing the soot, it also excites the C2 radicals, and the subsequent C2 fluorescence signal is detected. The signals from both techniques showed good correlation with soot volume fractions in the studied flame. The dependence of the signals on experimental parameters was studied, and the influence of interfering radiation, such as background flame luminosity and fluorescence from polyaromatic hydrocarbons, on studied signals was established. The potential of the two techniques for imaging of soot volume fractions in laboratory flames was demonstrated. Advantages and disadvantages of the studied techniques are discussed.