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 ha ve been investigated in sooting laboratory flames with known soot char acteristics. Two techniques were compared: Laser-Induced Fluorescence in C2 from Laser-Vaporized Soot (LIF(C2)LVS), and Laser-Induced Incand escence of soot (LII). The LII signal is the increased temperature rad iation from soot particles which have been heated to temperatures of s everal thousand degrees as a consequence of absorption of laser radiat ion. The LIF (C2)LVS technique is based on the production of C2 radica ls from laser-vaporized soot which occurs for laser intensities greate r-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 s tudied flame. The dependence of the signals on experimental parameters was studied, and the influence of interfering radiation, such as back ground flame luminosity and fluorescence from polyaromatic hydrocarbon s, on studied signals was established. The potential of the two techni ques for imaging of soot volume fractions in laboratory flames was dem onstrated. Advantages and disadvantages of the studied techniques are discussed.