Retrieval of soot aggregate morphology from light scattering/extinction measurements in a high-pressure high-temperature environment

Soot aggregates have been produced in a series of experiments based on the pyrolysis of ethylene in a shock tube facility, for pressure and temperature varying, respectively, in the range 10–15 bar and 1800–2000 K. In situ light scattering/extinction coupled measurements have been performed and the process has been followed with high spatial and temporal resolution (μm/μs). On the basis of the Kumar and Tien approach for randomly oriented aggregates [Kumar and Tien (1989) Combust. Sci. Technol. 66, 199–216], we investigated the sensitivity of the angular scattering pattern and of the dissymmetry ratio for straight chain and random cluster morphologies to the refractive indices, the number and diameters of primary spheres (spherules) in the agglomerate and the solid volume fraction of the cluster. The time variation of the scattered light intensity measured at different scattering angles θ (30°, 90°, 150°) is shown to enable deduction of the prevailing morphology of the (self-organizing) aggregate. At the end of the examined agglomeration process, the resulting soot aggregates appear to be structured on average as chains of 5–10 spherules with spherule diameter of ≈ 25–30 nm.