Influence of thermal ageing on oxidation performance and nanostructures of dry soot in diesel engine

Diesel soot subjected to high exhaust temperature suffers from thermal ageing, which is difficult to be removed by regeneration process. Based on the thermogravimetric (TG) analysis and images by high resolution transmission electron microscope (HRTEM), effects of thermal ageing temperature, ageing time and oxygen concentration on oxidation characteristic of soot are investigated. The activation energy of soot increases with the increase of ageing temperature and oxygen concentration. The activation energy increases rapidly when the ageing time is less than 45 min, and then it keeps in a value of 157 kJ/mol when the ageing time is between 45 and 60 min. Compared to the soot without thermal ageing, the shape of ageing soot particles presents shorter diameter and more regular circle by observing soot nanostructure. With the increase of ageing temperature, ageing time and oxygen concentration, the more stable structure of shell and core is shown in the basic carbon. The soot has an increased fringe length, decreased tortuosity and separation distance after thermal ageing process, which leads to the deepening of the disorder degree of soot nanostructures and reduction of soot oxidation activity. Consequently, the thermal ageing process should be avoided in order to optimize the active regeneration strategy.

Automated summary

The effects of thermal ageing on diesel soot depend on ageing temperature, time, and oxygen concentration. As these factors increase, the activation energy also increases, leading to enhanced stability of the soot structure.