AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Role Played by Charge in the Early Stages of Particle Formation and Growth of Titania and Soot Nanoparticles in High Temperature Flame Environment
GIRISH SHARMA, Mengda Wang, Huang Zhang, Xiaoqing You, Pratim Biswas, Washington University in St Louis
Abstract Number: 551 Working Group: Combustion
Abstract It is important to understand the early stages of particle formation and growth in high temperature flame environments for both nanoparticle synthesis and environmental applications. According to conventional understanding, at high flame temperatures, the particles collide with each other and coagulate to form larger particles. Contrary to this understanding, our previous work1 shows that during the early stages of particle formation and growth (< 2 nm), charged particle fraction is very high (> 95%), suggesting that in addition to neutral particle interactions, there are charged particle, and ion-particle interactions as well.
In this work, half-mini DMA is used to study the particle formation, and growth of soot and TiO2 nanoparticles in a premixed flame, and the role played by charge in the early stages (1 – 10 nm). Stagnation plane with hole-in-a-tube dilution probe with high dilution ratios (500-1500) is used to prevent coagulation in the sampling tube. First, positively and negatively charged blank flame ions are characterized for two different fuels (methane, and ethylene) in the presence of N2/Ar. For studying soot inception, experiments for different flame velocities with different HABs are performed. It is found that the positively charged particle size could be as small as 1.3 nm; whereas the smallest negatively charged particle is found to be 1.0 nm. Moreover, negatively charged particles are found to be slightly smaller in size, and slightly higher in total number concentration as compared to positively charged particles. Total particle size distribution is also measured to evaluate the percentage of charged particles. On the other hand, for material synthesis early stages of titania nanoparticles formation and growth are explored for different precursor concentrations, and height above the burner. The total PSD, and charge fraction provide more insights on the role played by charge on the particle formation, and growth for both TiO2 and soot nanoparticles starting from molecular clusters to 10 nm.
This work was supported by a joint NSF US and China grant to Washington University in St. Louis.