Effects of butanol isomers additions on soot nanostructure and reactivity in normal and inverse ethylene diffusion flames

摘要

This paper explored the effects of butanol isomers, n-butanol, iso-butanol, sec-butanol, and tert-butanol, as fuel-side additives on soot nanostructure and reactivity in ethylene inverse diffusion flames (IDF) and normal diffusion flames (NDF). The variations of structures and oxidation rates among the soot samples derived from ten different flames were studied and compared using high resolution transmission electron spectroscopy (HRTEM), Raman spectroscopy, thermogravimetric analyzer (TGA), surface area and porosimetry analyzer, and elemental analyzer. Results demonstrated that soot from IDF with the additions of butanol isomers had irregular shapes with film-like materials and highly heterogeneous nanostructures, which showed both amorphous carbon and fullerenic lamellae. The shells presented more prevalently in tent-butanol-doped IDF soot, which had the longest fringe length and smallest fringe tortuosity. Whereas in the NDF as butanol isomers were individually added, the soot samples were aggregated by several tens or hundreds nearly rounded particles. All the NDF soot exhibited a typical core-shell structure with extended and planar lamellae. Soot from sec-butanol added NDF presented the lowest degree of graphitization with the Shortest fringe length and largest fringe tortuosity. The TGA results revealed that the oxidation rates of the IDF soot particles were much higher than that of the NDF soot. Moreover, when butanol isomers were individually added in IDF, soot produced with n-butanol (1.34E-03 s(-1)) showed the highest reactivity with the least degree of crystallization in structure, followed by iso-butanol (1.31E-03 s(-1)), sec-butanol (1.29E-03 s(-1)) and tert-butanol (1.14E-03 s(-1)) in the sequence of reactivity. However, the oxidation rates of the soot samples generated from butanol isomers-doped NDF were in the order of sec-butanol (4.26E-04 s(-1)), tert-butanol (3.70E-04 s(-1)), n-butanol (3.52E-04 s(-1)) and iso-butanol (3.23E-04 s(-1)) from the highest to lowest. The results confirmed a relationship on structure-property between soot nanostructure and reactivity. (C) 2017 Elsevier Ltd. All rights reserved.