Optical and Chemical Characterization of Carbon Polymorphs Formed During Spray Combustion of Hydrocarbons

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Abstract
The spray combustion of liquid hydrocarbon fuels produces a large variety of structures containing a great number of carbon atoms (carbon polymorphs) which are or may generate toxic pollutants. These carbon polymorphs include compounds with a main aromatic character and larger aggregates as tar and soot. The spectroscopic properties of these polymorphs collected in a spray flame have been investigated by measurements of their u,v.-visible absorption spectra and fluorescence emission in the visible region. “In situ” spectroscopic characterization has been performed by both laser excited fluorescence and laser light scattering techniques. The comparison of optical data obtained “in situ” in a spray flame with those obtained from the chemical and spectroscopic analysis of the material sampled from the flame has been undertaken in order to attribute the u.v. absorption and the broad band laser excited fluorescence to specific classes of carbon polymorphs. During the heating-up of the fuel droplets there is an enrichment in polycyclic aromatic hydrocarbons and in higher molecular mass aromatic compounds, which eventually contain oxygen. These latter compounds exhibit a more intense fluorescence spectra in the visible region respect to the unsubstituted PAH.