Nanostructure evolution and reactivity of nascent soot from inverse diffusion flames in CO2, N2, and He atmospheres

Abstract

The micro and nanostructure evolutions and reactivity of nascent soot from n-butanol-doped ethylene inverse diffusion flames in CO2, N2, and He atmospheres were studied and compared. The thermophoretic sampling technique was employed to capture soot particles directly at different positions along the flame boundary. Transmission electron microscopy was applied to obtain the particle morphology evolution. Moreover, high-resolution transmission electron microscopy analysis, Raman spectroscopy analysis, thermogravimetric analysis, and X-ray photoelectron spectroscopy were performed to study the nanostructure and oxidation reactivity of soot from the quartz plate sampling. It was found that soot inception rate was reduced in CO2 atmosphere, indicating CO2 could inhibit soot formation through inception process. However, He promoted soot formation since the soot agglomerate amount was larger than those in flames with CO2 and N2. High correlations were found between soot nanostructure and reactivity. The soot from CO2 atmosphere had shortest fringe length and largest fringe tortuosity related with highest oxidation reactivity. On the contrary, soot from He diluted flame exhibited prevalent fullerenic-like nanostructures with evident large or small shells, and also had a higher carbonization degree resulting in lower oxidation reactivity. The surface oxygen content related to soot oxidation reactivity.