Soot maturity and absorption cross sections

Influence of soot aggregate size and internal multiple scattering on LII signal and the absorption function variation with wavelength determined by the TEW-LII method

“…Figure 6 shows that at a given wavelength, the absorption function ratio increases with increasing HAB. Therefore, the present results suggest that the absorption function ratio increases with increasing soot maturity, which is in contrast with the finding of López-Yglesias et al [13], who found that the absorption cross-sectional ratio, σabs(532 nm)/σabs(1064 nm), increases with decreasing soot maturity (related to the hydrogen content) in their study conducted in laminar co-flow diffusion flames. Although it is not completely clear about the causes of this qualitative difference between this study and that of López-Yglesias et al [13] with regard to the trend of soot absorption function ratio variation with soot maturity, there are at least two plausible explanations.…”

“…Therefore, the present results suggest that the absorption function ratio increases with increasing soot maturity, which is in contrast with the finding of López-Yglesias et al [13], who found that the absorption cross-sectional ratio, σabs(532 nm)/σabs(1064 nm), increases with decreasing soot maturity (related to the hydrogen content) in their study conducted in laminar co-flow diffusion flames. Although it is not completely clear about the causes of this qualitative difference between this study and that of López-Yglesias et al [13] with regard to the trend of soot absorption function ratio variation with soot maturity, there are at least two plausible explanations. One lies in the different theoretical relationship between E(m) and wavelength in the study of López-Yglesias et al [13], where E(m) was assumed to be proportional to wavelength λ raised to a power of (1 − ξ) with ξ being a function of soot maturity and having a value around unity (about 0.8-1.3).…”

“…Although it is not completely clear about the causes of this qualitative difference between this study and that of López-Yglesias et al [13] with regard to the trend of soot absorption function ratio variation with soot maturity, there are at least two plausible explanations. One lies in the different theoretical relationship between E(m) and wavelength in the study of López-Yglesias et al [13], where E(m) was assumed to be proportional to wavelength λ raised to a power of (1 − ξ) with ξ being a function of soot maturity and having a value around unity (about 0.8-1.3). The other is that the two investigated flames (premixed in the present 1 3 study and diffusion in the study of López-Yglesias et al) are likely to present different spatial structuration in terms of chemical structures mapping (localization of PAH's, soot precursors, and soot).…”

“…Further studies are needed to investigate how primary particle size affects the correction function to the aggregate absorption cross section and to understand the causes for the different findings between this study and that of López-Yglesias et al [13]. It is also important to further investigate soot E(m) values in different flames to gain better understanding of the relationship between soot E(m) values and soot maturity.…”

“…There seems a consensus in the literature that this value falls in the range of about 0.2-0.4, i.e., with a uncertainty of about a factor of 2. Nevertheless, investigations conducted so far tend to support that E(m) seems dependent on the type of fuel and the maturation of the soot particle [11][12][13]. It is well known that the soot absorption function is difficult to determine accurately and many methods have been proposed [12,[14][15][16][17][18][19][20][21][22].…”