Wei Jiangjun, He Chengjun, Zeng Yang
School of Automotive and Transportation Engineering, Hefei University of Technology, Hefei, Anhui 230009, China.
School of Automotive and Transportation Engineering, Hefei University of Technology, Hefei, Anhui 230009, China.
Sci Total Environ. 2024 Jan 1;906:167412. doi: 10.1016/j.scitotenv.2023.167412. Epub 2023 Sep 26.
Since the oxidation activity of nitrogen oxides on soot is obviously higher than that of O, it is one of the most effective means to improve soot combustion in diesel particulate filter (DPF) by fully utilizing the oxidation activity of nitrogen oxides in diesel exhaust. This paper investigated the physical properties (i.e. morphology, primary particle diameter, fractal dimension and nanostructure) and oxidation-induced fragmentation characteristics of diesel exhaust soot particles during oxidation degrees (0 %, 20 %, 50 % and 80 %) in different atmospheres (air, air-1000 ppm NO and air-2000 ppm NO). The results showed that during the oxidation process the variation trends of soot morphology in air and air-NO environments were similar, while the number and size of primary particles in an aggregate decreased and the fractal dimension of the aggregate increased with the presence of NO in air atmosphere. With the progress of oxidation, the nanostructure of soot particles became more ordered, while this variation trend was slowed down when NO was added to the air atmosphere. This is because soot particles oxidized in air-NO atmospheres showed less probability of internal oxidation but more external oxidation than those in air atmosphere. Over the oxidation process, the soot aggregate fragmentation rate presented a decreasing variation trend under each oxidizing atmosphere, with a higher aggregate fragmentation rate and more apparent variations in air-NO atmospheres. Moreover, in the air atmosphere, the probability of primary soot particle fragmentation showed a consistent upward trend, while the addition of NO slowed down this trend and showed an upward trend in stages 1(0 % ∼ 20 %) and 2(20 % ∼ 50 %), but a downward trend in stage 3(50 % ∼ 80 %). This suggests that the addition of NO reduces the probability of oxidants (especially O) entering the particles, which would lead to a decrease in the probability of primary soot fragmentation caused by internal oxidation.
由于氮氧化物对碳烟的氧化活性明显高于氧气，充分利用柴油机排气中氮氧化物的氧化活性是改善柴油颗粒过滤器（DPF）中碳烟燃烧的最有效手段之一。本文研究了在不同气氛（空气、空气 - 1000 ppm NO和空气 - 2000 ppm NO）中，氧化程度为0%、20%、50%和80%时，柴油机排气碳烟颗粒的物理性质（即形态、一次粒径、分形维数和纳米结构）以及氧化诱导的破碎特性。结果表明，在氧化过程中，空气和空气 - NO环境中碳烟形态的变化趋势相似，而在空气气氛中加入NO后，聚集体中一次颗粒的数量和尺寸减小，聚集体的分形维数增加。随着氧化的进行，碳烟颗粒的纳米结构变得更加有序，而在空气气氛中加入NO时，这种变化趋势减缓。这是因为在空气 - NO气氛中氧化的碳烟颗粒内部氧化的概率比在空气气氛中低，但外部氧化更多。在整个氧化过程中，在每种氧化气氛下，碳烟聚集体破碎率均呈下降趋势，在空气 - NO气氛中聚集体破碎率更高且变化更明显。此外，在空气气氛中，碳烟一次颗粒破碎的概率呈持续上升趋势，而加入NO减缓了这一趋势，在第1阶段（0% ∼ 20%）和第2阶段（20% ∼ 50%）呈上升趋势，但在第3阶段（50% ∼ 80%）呈下降趋势。这表明加入NO降低了氧化剂（尤其是氧气）进入颗粒的概率，这将导致内部氧化引起的碳烟一次破碎概率降低。
