Raman Spectroscopy of Soot Sampled in High-Pressure Diffusion Flames

The effect of pressure on soot particle nanostructure has been investigated by Raman spectroscopy. For the first time soot samples produced in a set of coflow methane-air laminar diffusion flames stabilized in a high-pressure combustion chamber, and collected by thermophoresis, have been analyzed to obtain chemical/structural information. The first-order Raman spectra of soot particles collected at several elevated pressures have been analyzed and compared. As a result, within the investigated range of pressures, i.e., from 10 to 20 bar, our measurements show that soot nanostructure does not depend on the pressure conditions. Changes in soot nanostructure were only observed as a function of flame residence time. The results herein presented are particularly relevant by considering the importance of nanostructure on the soot reactivity toward oxidation and on the fact that soot from practical combustion devices is mostly produced at high pressure.