Effect of Temperature on Morphologies and Microstructures of Soot Particles in the Diesel Exhaust Pipe

Insulating cotton was used to change the airflow temperature in the exhaust pipe of a diesel engine, and soot particles at different positions in the exhaust pipe under different operating conditions were collected. The morphologies and microstructures of soot particles were observed by high-resolution transmission electron microscopy (HRTEM). The characteristic parameters, including the mean primary particle diameter (d(p)), radius of gyration of soot aggregate (R-g), fractal dimension of soot particle (D-f), carbon layer spacing (D-s), and carbon layer torsion resistance (T-f), were statistically analyzed. The changes in each characteristic parameter before and after adding insulating cotton were compared. After installing the cotton, soot particles still grew through surface chemical reactions and physical processes in the diesel exhaust pipe, the agglomeration becomes more and more prevalent, the particle size increased, and D-f increased. The increase in the airflow temperature in the exhaust pipe promoted the surface growth of primary soot particles and enhanced the turbulence, which made the chain-like soot particles more likely to reunite under the action of turbulent eddies. Consequently, R-g decreased and D-f increased. Furthermore, the average D-s and T-f of primary soot particles deceased, especially under high loads. This indicated that the increase in the temperature of the exhaust pipe was conducive to the graphitization of primary soot particles.