Candle flame soot sizing by planar time-resolved laser-induced incandescence

<jats:title>Abstract</jats:title><jats:p>Soot emissions from flaming combustion are relevant as a significant source of atmospheric pollution and as a source of nanomaterials. Candles are interesting targets for soot characterization studies since they burn complex fuels with a large number of carbon atoms, and yield stable and repeatable flames. We characterized the soot particle size distributions in a candle flame using the planar two-color time-resolved laser induced incandescence (2D-2C TiRe-LII) technique, which has been successfully applied to different combustion applications, but never before on a candle flame. Soot particles are heated with a planar laser sheet to temperatures above the normal flame temperatures. The incandescent soot particles emit thermal radiation, which decays over time when the particles cool down to the flame temperature. By analyzing the temporal decay of the incandescence signal, soot particle size distributions within the flame are obtained. Our results are consistent with previous works, and show that the outer edges of the flame are characterized by larger particles (<jats:inline-formula><jats:alternatives><jats:tex-math>$$\approx 60\,\hbox {nm}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>≈</mml:mo><mml:mn>60</mml:mn><mml:mspace /><mml:mtext>nm</mml:mtext></mml:mrow></mml:math></jats:alternatives></jats:inline-formula>), whereas smaller particles (<jats:inline-formula><jats:alternatives><jats:tex-math>$$\approx 25\,\hbox {nm}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>≈</mml:mo><mml:mn>25</mml:mn><mml:mspace /><mml:mtext>nm</mml:mtext></mml:mrow></mml:math></jats:alternatives></jats:inline-formula>) are found in the central regions. We also show that our effective temperature estimates have a maximum error of 100 K at early times, which decreases as the particles cool.</jats:p>