Formation mechanism of Particulates Emitted from Diesel Engines

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To clarify particulate formation processes and factors to decrease it, we investigate the thermal cracking and condensation polymerization processes of various fuels in nitrogen atmosphere using a thermal cracking apparatus. The paraffin fuels which are the principal ingredient of gas oil are thermally cracked to form lower boiling point hydrocarbons, and the particulate was then formed via the polycyclic aromatic hydrocarbons. However, the benzene rings of the aromatic fuels are little thermally cracked to form polycyclic aromatic hydrocarbons.Next, we examined a vacuum sublimation method to analyze polycyclic aromatic hydrocarbons of a small quantity of sample gas. It was carried out at the sublimation temperature 300 C, vacuum pressure 0.05 Pa, sublimation time 30 minutes and condensation column temperature -70 C.With a fluid reaction tube and nitrogen atmosphere, we investigate the amount and configuration of particulate, and analyzes polycyclic aromatic hydrocarbons of fuels with different molecular structure and carbon number by above method. As the results, starting formation temperature of particulate depends on the fuel properties. As the C/H ratio increases, the amount of particulate increases. The soot precursor has at most three, four or five rings of polycyclic aromatic hydrocarbons. The formation of particulate takes place via polycyclic aromatic hydrocarbons by condensation polymerization and dehydrogenation.