Experimental and Modeling Investigations on Soot Formation of Ethanol, n-Butanol, 2,5-Dimethylfuran, and Biodiesel in Diesel Engines

The soot formation in the combustion of four oxygenated fuels on a single-cylinder engine has been investigated experimentally and numerically. To accomplish this objective, a reduced combustion mechanism was proposed for the modeling studies, which has been extensively validated. Then direct injection compression ignition experiments fueled with diesel, biodiesel, and its blends with 20% volume fraction of ethanol (E20), n-butanol (B20), and 2,5-dimethylfuran (D20) have been conducted. In the three-dimensional (3-D) modeling studies, the reduced mechanism can well predict the experimental combustion and soot emission results. In contrast to the combustion phasing, the soot emissions for the five fuels were sequenced as diesel > biodiesel > B20 > D20 > E20, which was mainly due to the different oxygen content and fuel reactivity in the spray-combustion processes. Furthermore, 0-D modeling investigations were conducted as well to clarify the effects of the different oxygenated structures on the polycyclic aromatic hydrocarbons (PAHs) formation under homogeneous condition. It was shown that, for the five pure fuel cases, the sooting tendencies were sequenced as ethanol < n-butanol < methyl-decanoate < n-heptane < 2,5-dimethylfuran. According to the reaction pathway analyses, oxygenated fuels with a longer carbon chain molecular structure could produce more intermediate species, which favor the PAHs and soot formation. However, much more phenol and cyclopentadienyl radical can be produced due to the special cyclic structure of 2,5-dimethylfuran, resulting in the highest soot formation among these investigated fuels.