Influence of the cumulative effects of multiple laser pulses on laser-induced incandescence signals from soot |
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Authors: | S De Iuliis F Cignoli S Maffi G Zizak |
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Institution: | 1.CNR-IENI, sede di Milano,Milan,Italy |
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Abstract: | The effect of multiple laser pulses reaching soot particles before an actual laser-induced incandescence (LII) measurement
is investigated in order to gain some insights on soot morphological and fine structure changes due to rapid laser heating.
Soot, extracted from a premixed and a quenched diffusion flames, is flowing through a tubular cell and undergoes a variable
number of pulses at different fluence. The response of soot is studied by the two-color LII technique. Transmission electron
microscopy (TEM) analysis of laser-modified soot aggregates from the diffusion flame is also presented. The results indicate
that even at low laser fluences a permanent soot transformation is induced causing an increase in the absorption function
E(m). This is interpreted as an induced graphitization of soot particles by the laser pulse heating. At high fluences the vaporization
process and a profound restructuring of soot particles affect the morphology of the aggregates. Soot from diffusion and premixed
flames behaves in a similar way although this similarity occurs at different fluence levels indicating a different initial
fine structure of soot particles. |
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