Impact of n-Hexanol Blending on Morphology, Nanostructure, Graphitization, and Oxidation Characteristics of Diesel Particles

As a promising alternative fuel with favorable properties and attractive prospects, the application of n-hexanol in diesel engines has aroused the interest of researchers. This study investigated the effects of mixing with n-hexanol on the morphology, nanostructure, graphitization, and oxidation reactivity of soot particles generated from a diesel engine. Experiments were performed on a turbocharged, four-cylinder direct-injection diesel engine fueled with D100 (neat diesel fuel), DH15 (15% n-hexanol and 85% diesel, v/v), and DH30 (30% n-hexanol and 70% diesel, v/v), respectively. Under the constant torque of 125 N·m, two typical speeds of 1370 and 2150 rpm were selected. Transmission electron microscopy (TEM), Raman spectroscopy (RS), and thermogravimetric analysis (TGA) were used to characterize particulate samples. TEM images showed that DH15 and DH30 particles had smaller primary particle diameters in comparison with neat diesel particles. Moreover, with the increase of the n-hexanol content in mixtures, the interlayer distance increased, indicating a more disordered nanostructure. RS results showed that soot samples generated from n-hexanol/diesel blended fuels had a lower degree of graphitization with larger ID1/IG and AD1/AG and more amorphous carbon with larger ID3/IG and AD3/AG. Based on TGA, it can be deduced that the DH30 soot sample obtained at the engine speed of 1370 rpm was easier to be oxidized in the DPF regeneration process for an 8.23% reduction in Tmax compared with D100 soot. Furthermore, activation energy of soots sampled at the engine speed of 2150 rpm decreased from 123.0 kJ/mol for D100 soot, to 109.6 kJ/mol for DH15 soot, and to 101.2 kJ/mol for DH30 soot, respectively. Regarding the effect of engine speeds on physicochemical characteristics of particles, results showed that the soot has higher oxidation activity under higher engine speed.