Formation mechanism of Particulates Emitted from Diesel Engines

为了阐明颗粒形成过程和减少颗粒形成的因素，我们用热裂解装置研究了不同燃料在氮气气氛中的热裂解和缩合聚合过程。石蜡燃料是汽油的主要成分，它被热裂解形成低沸点的碳氢化合物，然后通过多环芳烃形成颗粒。然而，芳烃燃料中的苯环很少被热裂解形成多环芳烃。接下来，我们研究了一种真空升华方法来分析少量样品气中的多环芳烃。在升华温度为300℃、真空度为0.05Pa、升华时间为30min、冷凝塔温度为-70℃的条件下，利用流体反应管和氮气气氛考察了颗粒的数量和形态，并用上述方法分析了不同分子结构和碳数的燃料中的多环芳烃。结果表明，颗粒的起始形成温度取决于燃料的性质。随着C/H比的增加，颗粒物的数量增加。烟尘前体最多具有三环、四环或五环多环芳烃。颗粒的形成是通过多环芳烃通过缩合聚合和脱氢来实现的。

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.