Investigation on the adsorption characteristics and influencing factors of diesel engine exhaust particulate matter

Abstract

In the exhaust pipe, the adsorption process of diesel exhaust particulate matter (PM) is affected by the combination of its adsorption capacity and the environment. A diesel exhaust particle collection system was established to collect samples with different environmental conditions. The adsorption capacity of the samples was characterized by an isothermal adsorption test. Changes in sample characteristics were investigated by scanning electron microscope and thermogravimetric analyzer. The correlation analysis of the factors influencing the adsorption process was performed. The results showed that the diesel exhaust particulate matter has adsorption capacity, the pore diameter is distributed continuously in the range of 8 to 80 nm, and the specific surface area and pore structure parameters are similar to carbon black and belong to the category of mesopores and macropores. As the engine speed increased from 1500 to 3600 r·min^-1, the specific surface area of samples increased from 65.408 to 101.885 m²·g^-1, and the pore volume expanded from 0.093 to 0.152 mL·g^-1, with a more complex pore structure and enhanced adsorption capacity. The samples at the outlet of the exhaust pipe had increased box dimension (D_B), moisture, and soluble organic fraction (SOF) content compared to the samples at the inlet of the exhaust pipe. The activation energies (E) of the three samples were reduced by 34.77 kJ∙mol^-1, 38.88 kJ∙mol^-1, and 47.43 kJ∙mol^-1, respectively. Among the influencing factors, the increase of hydrocarbon concentration contributes to the increase of adsorption volume and the reduction of E. The increase of the average temperature inhibits the increase of the D_B, and the increase of the temperature difference between the inlet and outlet facilitates the adsorption of water and SOF by samples. The reduction of adsorption time is one of the main reasons for delaying the increase of D_B. Average pore diameter has the largest positive correlation with the variation amount of D_B, and the growth of the specific surface area and pore volume is the dominant reason for the improvement of adsorption capacity and oxidation activity.

Keywords: Adsorption; Diesel engine; Micromorphology; Oxidation properties; PM; Soluble organic fraction.