Morphology analysis of soot particles from a modern diesel engine fueled with different types of oxygenated fuels

Abstract

Using a transmission electron microscopy (TEM), the morphological characteristic variations of exhaust soot particles have been studied on a modern diesel engine fuelled with a commercial diesel fuel (D100, as a baseline fuel) and three different oxygenated fuel blends with the same oxygen content, including a 11.5% methanol blend (M11.5), a 8.3% dimethyl carbonate blend (DMC8.3), and a 13% dimethyl methane blend (DMM13). The results showed that oxygenated fuel blends emitted smaller soot primary particles with respect to neat diesel, with the most significant decrease in M11.5 followed by DMM13 and DMC8.3. Similar variations with primary particle diameter were found in the decrease of the mean radius of gyration, mean primary particle number and estimated mass for an agglomerate when making comparisons among diesel and the three oxygenated fuel blends. Aggregates shape analysis showed that M11.5 soot had the minimal trend to form a rather circular structure and maximal boundary irregularity among the four fuels, while all soot particles showed larger deviation to the sphere (i.e. higher elongation) regardless of fuel type used. In addition, both mass and perimeter fractal dimension showed consistent results for diesel and the three oxygenated fuel blends, with the particle aggregates being the least compacted morphology for M11.5, followed by DMM13, DMC8.3 and diesel. Therefore, compared to diesel, the exhaust soot particles from the oxygenated fuel blends (especially for M11.5) are more prone to be trapped (lowest fractal dimension) and display a higher reactivity towards oxidation (smallest primary particle size).