Variations of the Soot Precursors Chemical Composition Induced by Ethanol Addition to Fuel

In this study, conventional analytical methods such as infrared spectroscopy, H-1 NMR, elemental analysis, and vapor pressure osmometry were combined to calculate the average structural parameters of the soot precursor material present in the soluble Organic fraction (SOF) of young soot of aliphatic and aromatic inverse diffusion flames doped with ethanol. The structural parameters were classified in two groups:. the first one is the parameters that describe the aromatic character, and the second describes the aliphatic Character of the Samples. The results of this study indicated that the addition of ethanol to aliphatic or partially aliphatic fuels produces less SOF due to an increase in the oxidation process, whereas the addition of ethanol into aromatic fuels caused an increase in this fraction. Additionally, it was observed that the ethanol addition to aromatic flames caused an increase in the fraction of aromatic carbon substituted by hydrogen (f(aHa)) of SOF samples, which leads to a reduction of the average size of the aromatic cluster (R-a). This result, along with an increase of low molecular weight PAHs, could explain the increase in chloroform solubility. A similar behavior occurs in the aliphatic flames, where the aromatic component. of SOF decreases due to ethanol addition; however, the reduction. of the SOF only can be explained by an increase in the soot precursors oxidation caused by the OH radical coming from ethanol. Although: the oxidation and pyrolysis are parallel processes in combustion, the extension of each of one will depend on the nature of the initial fuel; so that the ethanol addition will increase the oxidation process in aliphatic flames and promotes the formation of low molecular weight PAHs in the aromatic ones.