(583m) Nascent Soot Formation By Agglomeration and Surface Growth

Georgios A. Kelesidis, Eirini Goudeli, Sotiris E. Pratsinis

Particle Technology Laboratory, Institute of Process Engineering,

Department of Mechanical & Process Engineering, ETH Zurich, Switzerland

Nascent soot particles of mobility size 1 – 10 nm are the building blocks of diesel soot, a major environmental pollutant, but also carbon black, a valuable commodity material used in reinforcing tires and other industrial rubber products. Recently, however, major concerns have been raised, since microscopy and mass-mobility measurements have revealed the existence of ultrafine aggregates during nascent soot formation. So, their impact on climate, health and nanomaterials manufacturing needs to be determined accurately.

Here, Discrete Element Model (DEM) simulations are used to investigate the dynamics of nascent soot particle growth after nucleation accounting for simultaneous surface growth and agglomeration in the absence of soot oxidation (Kelesidis et al., 2017). The model is validated with theoretical expressions for pure agglomeration (Goudeli et al., 2015) as well as with surface growth with and without coagulation at full coalescence. The evolution of nascent soot structure is benchmarked against previous numerical studies.

Nascent soot growth by agglomeration with or without acetylene molecule reaction (pyrolysis) is compared to that by full coalescence. Neglecting the non-spherical or fractal-like nature of soot underestimates its aggregate polydispersity up to 40 %. The DEM-derived size distributions of soot growing by agglomeration with surface growth are in good agreement with microscopy (Schenk et al., 2013) and mass-mobility measurements (Camacho et al., 2015) of nascent soot produced in ethylene flames, indicating that surface growth narrows down soot size distributions at low heights above the burner, consistent with literature. The evolution of nascent soot structure from spheres to aggregates quantified by the mass fractal dimension and mass-mobility exponent is also in excellent agreement with experiments (Schenk et al., 2013; Camacho et al., 2015). The effect of soot volume fraction on nascent soot morphology is elucidated. Based on the aggregate projected area, a scaling law is derived for the number and size of the nascent soot primary particles from mass-mobility measurements.

References:

Camacho, J., Liu, C., Gu, C., Lin, H., Huang, Z., Tang, Q., You, X., Saggese, C., Li, Y., Jung, H., Deng, L., Wlokas, I., Wang, H. (2015) Combust. Flame 162, 3810-3822.

Kelesidis, G.A., Goudeli, E., Pratsinis, S.E. (2017) Proc. Combust. Inst. 36, 29-50.

Goudeli, E., Eggersdorfer, M.L. and Pratsinis, S.E. (2015) Langmuir 31, 1320-1327.

Schenk, M., Lieb, S., Vieker, H., Beyer, A., Golzhauser, A., Wang, H., Kohse-Hoinghaus, K. (2013) PhysChemPhys 14, 3248-3254.