Soot properties in ethylene inverse diffusion flames blended with different carbon chain length alcohols

Abstract

This study was devoted to the characterization of soot properties in ethylene inverse diffusion flames with different carbon length alcohols, which mainly contained the soot morphology, soot nanostructure, and oxidation reactivity. Ethanol, n-butanol, n-hexanol, and n-octanol were selected as the fuel additives. For all blended flames, a 30% volume fraction of ethylene was substituted by different alcohol additives, and the flow rates of the alcohols were adjusted to achieve the same number of carbon atoms. A combination of the thermophoretic sampling technique and the quartz plate sampling method was applied to gain soot features. The transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and thermogravimetric analysis (TGA) were used. The results showed that soot production was reduced with the addition of all alcohols, and the minimum soot yield was observed with ethanol addition. The soot-reducing ability gradually decreased as the alcohols move higher. The sizes of the primary particles and soot aggregates increased slightly faster with the increasing carbon chain length. Furthermore, the soot generated from higher alcohol-doped flame has a higher degree of graphitization with longer fringe length and smaller fringe tortuosity. The four different alcohol additives all could improve soot oxidation reactivity. There was a correlation between soot oxidation reactivity and the carbon chain length of the alcohols that the longer carbon chain of these alcohol additives led to lower soot reactivity.