Chemical Features of Particles Generated in an Ethylene/Ethanol Premixed Flame

An ethylene\ethanol premixed flame has been investigated to elucidate the effect of ethanol addition on particle morphology and chemical features in controlled flame conditions. In situ optical techniques and ex situ online particle size distribution measurements showed that soot formation is strongly reduced for the effect of ethanol addition to ethylene and that soot particle size is much lower with respect to the size of the soot particles formed in a neat ethylene flame operated under the same combustion conditions. It was also noticed that the formation of nanoparticles with sizes smaller than 10 nm is not significantly affected by ethanol addition to ethylene; their concentration remains practically unchanged or even increases for the effect of ethanol addition. Particles produced in the ethylene/ethanol flame showed a higher reactivity with respect to the ethylene-generated particles. Raman spectra indicated that the presence of ethanol inhibits the aromatization process, showing, on average, a smaller size of the aromatic island within the particles. Ultraviolet-visible analysis confirmed this finding, showing a marked molecular character for the particles collected in the ethylene/ethanol flame with respect to the neat ethylene flame, especially for the particles with sizes smaller than 20 nm. Finally, Fourier transform infrared spectra evidenced the presence of oxygen functionalities onto the particles formed when ethanol is used; the molecular character and bonded oxygen atoms can contribute to the major reactivity of the ethanol-generated particles, as also evidenced by thermogravimetric analysis.