On the consideration of signal trapping for soot sizing by angular light scattering in laminar flames

Abstract

Soot particles are known to be harmful to health and the environment, and reducing their production in industrial systems is a crucial task in the pursuit of green energy production. Characterization and accurate modeling of these particles are essential yet complex. In particular, information on aggregate sizing remains limited. Angular light scattering is an established in-situ method for precise, spatially resolved, non-intrusive characterization of soot aggregates. However, the associated post-processing is prone to various error sources. Specifically, signal trapping during light scattering is suspected to lead significant errors. Moreover, current techniques for reconstructing the line-of-sight integrated scattering signal (Abel inversion) are inherently noisy. This work addresses both issues by implementing a noise-free Abel inversion method based on piecewise spline functions. This method accounts for signal trapping and can be applied to any axisymmetric and spatially continuous flame. The correction for the signal trapping effect relies on extinction measurements from the line-of-sight attenuation (LOSA). The technique is tested on a canonical laminar diffusion ethylene flame at five different angles. The impact of this correction is evaluated on the equivalent monodisperse radius of gyration, denoted as $R_g^{\ast }$, and the forward scattering coefficient, represented as ${\kappa }_{vv}\left(0^{\circ }\right)$. The results show that the calculation of $R_g^{\ast }$ is robust regarding signal trapping effect. However, correcting for this effect significantly increases ${\kappa }_{vv}\left(0^{\circ }\right)$.