AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Influence of Temperature and Dilution on Final Soot Nanostructure
JUSTIN DAVIS, Igor Novosselov, University of Washington
Abstract Number: 527 Working Group: Combustion
Abstract Morphological evolution of nascent to mature combustion-generated particles is of interest due to changes in particle optical properties, density, chemical composition, and their effect on human health. In this work, the nanostructure of primary soot particles is investigated using argon dilution in laminar ethylene, ethane, and methane flames. A co-flow reactor oriented downwards allows for precise control on combustion conditions due to increased flame stability brought on by competing buoyant and convective forces. The dilution is varied from 0% to 90% by volume to investigate particle formation in temperature ranges from 1650 to 1950 K. High-resolution transmission electron microscopy displays different levels of particle maturity, from young soot with minimal order to mature particles with a core-shell nanostructure. A novel image processing algorithm helps to quantify differences in soot nanostructure. Graphene-like flakes that comprise young and mature soot particles are around the same size, indicating the molecular weight of PAHs is similar for young and mature soot. However, the graphene-like flake curvature decreases and the percentage of stacked fringes increases significantly for high temperature (low dilution) flames. The reduction in curvature suggests the more planar PAHs have greater C/H ratios, independently verified by total organic carbon analysis. Overall, this study suggests the driving factor of soot maturity is a reduction in steric hindrance due to carbonization kinetics at high flame temperatures. These results can be used for validation of soot modeling approaches and to improve the understanding of structural changes as soot particles traverse the flame front.