Optical properties of incipient soot

The exact knowledge of the optical properties of soot nanoparticles is fundamental for several aspects including the correct determination of the soot concentration in combustion environments using optical diagnostics and the correct estimation of the environmental impact of the emitted particles. Although extensive researches over the years have led to a substantial agreement on the optical properties of mature soot particles, the optical properties of the incipient soot nanoparticles are still uncertain. From the particle inception point to the formation of large and more mature soot particles, the evolution of the optical properties must account for variations due to the size and the physicochemical transformation of the investigated particles. This work aims to determine the refractive index and optical properties of inception particles formed in lightly sooting flames. A previous determination based on in - situ light absorption and scattering measurements is revisited taking advantage of particle size measurements by differential mobility analysis. The spectral dependencies of the optical properties are derived by the Kramers-Kr onig analysis of the ex - situ VUV-NIR light absorption measurements. Results confirm the strong decrease in the absorptivity in the vis-NIR region of inception particles with unimodal size distribution and d 63 & SIM;3 nm, and confirm a strong size dependency of soot optical properties. The thermal-optical analysis of the sampled particles shows that the particle mass & COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

Accurate understanding of the optical properties of soot nanoparticles is crucial for applications such as measuring soot concentration in combustion environments and assessing environmental impact. While there is considerable agreement on the optical properties of mature soot particles, the properties of incipient soot nanoparticles remain uncertain. This study revisits the determination of refractive index and optical properties of inception particles in lightly sooting flames. By analyzing both light absorption and particle size measurements, the study confirms a significant decrease in absorptivity in the visible to near-infrared region for inception particles with a unimodal size distribution of d 63 & SIM;3 nm. The results also highlight the strong dependence of soot optical properties on particle size.