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

Ignacio Verdugo,Andrés Fuentes,Juan José Cruz,Emilio Álvarez,Luís Fernando Figueira Da Silva,Pedro Reszka

doi:10.1038/s41598-020-68256-z

Abstract

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 (approx 60,hbox {nm}), whereas smaller particles (approx 25,hbox {nm}) 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.

Highlights

Soot emissions from flaming combustion are relevant as a significant source of atmospheric pollution and as a source of nanomaterials
Particle size distribution is inferred by employing laser fluences that are lower than those used for for applying the classic Laser induced incandescence (LII) technique, decreasing the soot sublimation effects, and allowing an energy balance equation applicable to this problem to be presented and solutions to be obtained iteratively to account for the different particle sizes
The planar two-color time-resolved laser induced incandescence (2D-2C TiRe-LII) technique was used to characterize a candle flame operating below the smoke point

Summary

Introduction

Soot emissions from flaming combustion are relevant as a significant source of atmospheric pollution and as a source of nanomaterials. Candle flame luminosity is due to the emission of thermal radiation by incandescent carbon-based nanoparticles, commonly known as soot These particles are produced within the reaction zone by a complicated set of chemical r eactions[10,11] and represent an important source of particulate matter pollution. Particle size distribution is inferred by employing laser fluences that are lower than those used for for applying the classic LII technique, decreasing the soot sublimation effects, and allowing an energy balance equation applicable to this problem to be presented and solutions to be obtained iteratively to account for the different particle sizes In this case, an effective soot particle aggregate temperature is measured using time-resolved two-color optical pyrometry, which is compared with a numerical LII model to infer a mean soot particle size[28,29]. Planar TiRe-LII measurements use intensified cameras (ICCD) to capture the incandescence signals at different delay times after the laser pulse[24,31,32,33]

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