The effect of butanol isomers on the formation of carbon particulate matter in fuel-rich premixed ethylene flames

The effect of the butanol isomers on carbon particulate matter formation was studied by substituting up to 20% of the total carbon of ethylene, fed to premixed flames with different equivalence ratios, with the four butanol isomers. Soot and condensed-phase nanostructures were tracked by means of particle size distribution (PSD) measurements and laser induced emission spectroscopy, namely fluorescence and incandescence. Butanol isomers, especially t-butanol, significantly reduced the total amount and the size of the soot particles, whereas a negligible effect was detected on condensed-phase nanostructures. PSDs were measured along with the aromaticity and functionalities of the carbon particulate matter thermophoretically sampled in the highest equivalence ratio condition. No significant differences were found among the different butanol isomers neither in the soot aggregate size, as measured by size exclusion chromatography, nor in the aromaticity, as evaluated by Raman and UV-vis spectroscopy, of the particulate matter. Conversely, FTIR analysis showed that carbon particulate matter produced from 1-butanol and t-butanol-doped flames contained larger amounts of oxygen in form of C = O, C-O-C and OH functionalities. However, most of the differences in the oxygen functionalities disappeared after dichloromethane (DCM) treatment, suggesting that these oxygenated moieties belong to the condensed-phase nanostructures, soluble in DCM, rather than to soot particles.