(445a) Light Scattering from Soot Nanoparticle Agglomerates

Combustion-generated nanoparticles during material synthesis and energy generation (e.g. for transportation and electric power) as well as open fires form fractal-like structures by agglomeration and surface growth [1]. Yet, their optical properties are calculated typically by Rayleigh or Mie theories for spheres impeding characterization by optical diagnostics and selective sensing [2]. For example, fire (smoke) detectors are not selective enough to carbon black or soot light scattering and thus produce false alarms costing up to 1 billion £/y in United Kingdom alone [3].

Here, Soot agglomerate structure and optical properties are simulated by coupling Discrete Element Modeling (DEM) for surface growth and agglomeration with the Discrete Dipole Approximation (DDA) to account for multiple scattering [4]. The soot agglomerate morphology and light scattering estimated by DEM-DDA are compared to mass-mobility, microscopy and light scattering measurements in premixed ethylene flames. Using the Rayleigh-Debye-Gans theory and neglecting necking (aggregation) and polydispersity of constituent primary particles underestimates the differential scattering cross-sections for vertically-, C_v, and horizontally-polarized incident light, C_h, measured in premixed ethylene flames up to 50 %. In contrast, the DEM-derived C_v and C_h are in excellent agreement with the data. Thus, the DEM-DDA can be used to optimize optical diagnostics for soot or carbon black characterization and selective sensing by fire detectors.

References:

[1] Kelesidis, G. A., Goudeli, E., & Pratsinis, S. E. (2017). Carbon, 121, 527-535.

[2] Keller, A., Loepfe, M., Nebiker, P., Pleisch, R., & Burtscher, H. (2006). Fire Safety J., 41, 266-273

[3] Chagger, R., & Smith, D. (2014). http://www.bre.co.uk.

[4] Kelesidis, G. A., Kholghy, M. R., Zuercher, J., Robertz, J., Allemann, M., Duric, A., & Pratsinis, S. E. (2019). Powder Technol., doi.org/10.1016/j.powtec.2019.02.003.