Laser-induced incandescence (2λ and 2C) for estimating absorption efficiency of differently matured soot
Sandra Török, Manu Mannazhi, Per-Erik Bengtsson
Abstract
Abstract Two-wavelength and two-color laser-induced incandescence (2 λ –2C-LII) was used to study the absorption properties of three types of cold soot of different maturity from a mini-CAST soot generator. LII fluence curve analysis allowed for estimating absorption wavelength dependence in terms of dispersion coefficients ξ by the use of two excitation wavelengths (532 and 1064 nm). The estimated ξ (based on E ( m, λ ) ∝ λ 1−ξ ) spanned from ~ 1.2 for the mature soot, up to 2.3 for the young soot. The results for the mature soot showed good agreement with previous measurement using multi-wavelength extinction. For the young soot, however, some discrepancy was observed suggesting a weaker wavelength dependence (lower ξ ) from the LII fluence analysis. Furthermore, an estimation of the E ( m, λ ) for the different types of soot was done from the experimental fluence curves with temperature analysis in the low-fluence regime and simulations using an LII model. Additionally, uncertainties and limitations were discussed. Finally, it should be pointed out that caution has to be taken when interpreting 2 λ -LII results to obtain quantitative absorption properties of less mature soot, which may be influenced by thermal annealing during the laser pulse and by absorption from non-refractory species externally/internally mixed with the soot.