=Paper=
{{Paper
|id=None
|storemode=property
|title=Pulsed laser heating of differently aged soot probed using LII and LES
|pdfUrl=https://ceur-ws.org/Vol-865/Olofsson.pdf
|volume=Vol-865
}}
==Pulsed laser heating of differently aged soot probed using LII and LES==
<pdf width="1500px">https://ceur-ws.org/Vol-865/Olofsson.pdf</pdf>
<pre>
                   Pulsed laser heating of differently aged soot
                            probed using LII and ELS
         Nils-Erik Olofsson1 Jonathan Johnsson2 Henrik Bladh3 Per-Erik Bengtsson4
               Combustion Physics, Lund University, Box 118, SE-22100, Lund, Sweden
         1                                          2
          E-mail: nils-erik.olofsson@forbrf.lth.se, E-mail: jonathan.johnsson@forbrf.lth.se,
             3                                   4
              E-mail: henrik.bladh@forbrf.lth.se, E-mail: per-erik.bengtsson@forbrf.lth.se

  Laser‐induced incandescence (LII) is a laser‐based technique for measuring soot particle sizes
  and soot volume fractions e.g. in flames, furnaces and exhaust gases. The basic principle of the
  technique is a rapid heating of soot particles with pulsed laser light and then detecting the
  increased incandescence. During the last two decades LII has been extensively refined and
  evolved to one of the standard techniques when conducting in situ measurements on soot
  particles. However, there are still refinements to be made, not least in understanding the
  interaction between laser light and soot, which is crucial information in the evaluation process
  where this interaction is modeled together with the subsequent cooling of the soot particles.
           In this work the heating and vaporization effects of the LII laser pulse on differently
  aged soot have been studied by a combination of LII and elastic light scattering (ELS) with an
  experimental procedure similar to the one used in [1], but with additional possibility for
  pyrometry using two‐color LII. By using an Nd:YAG laser at 1064 nm for the LII and another at
  532 nm for ELS, and intersecting the laser beams in the probe volume, the elastic scattering
  can be utilized to probe heating and vaporization effects of the 1064 nm laser light. To
  generate the soot particles a McKenna type burner has been used, where the soot growth can
  be followed from nascent soot particles close to the burner surface to more mature soot
  higher up in the flame.
           Results show a significant difference as a function of height above burner (HAB) as
  seen in Fig. 1. This behavior could be explained by a variation in both the absorption function,
  E(m), and the sublimation threshold at different HAB i.e. for differently aged soot.
  Furthermore the results reveal an effect not discussed in [1], namely a slight increase of the
  scattering signal from soot just before the rapid decrease due to vaporization, seen in Fig. 2.




                                                                Figure 2 Normalized ELS signal before and after an LII laser
                                                                pulse with fluence 0.3 J/cm2 at 10 mm HAB.
Figure 1 Normalized ELS signal before and after an LII laser
pulse with fluence 0.3 J/cm2. Top plot shows measurement at 8
mm HAB and bottom plot at 10 mm HAB.

  [1] G. D. Yoder, P. K. Diwakar, D. W. Hahn ”Assessment of soot particle vaporization effects
  during laser‐induced incandescence with time‐resolved light scattering”, Appl. Opt. 44 (2005)



                    5th international workshop on Laser-Induced Incandescence
                     May 9-11, 2012, Palais des Congrès, Le Touquet, France

</pre>