Soot Sampling And Nanostructure Analysis In Diesel Spray Flame

Diesel engines have been widely used in the transportation industry for their high thermal efficiency,power,economy and durability.However,as the number of diesel engines continues to increase,the pollution is becoming more and more serious.Diesel emissions include particulate matter(PM)and nitrogen oxides(NO_x),both of which have a trade-off relationship.The main component of diesel PM is soot particles,which can accumulate in the depths of the human respiratory system and cause health problems.Therefore,countries around the world have paid great attention to the research on the mechanism of diesel particulate generation.In this paper,the Constant Volume Pre-combustion Cell was modified.The soot sampling probes were designed based on the thermophoresis sampling principle.The soot particles in different axial positions,different loads and different oxygen concentrations of the jet flame were collected and transmitted by TEM.TEM and high resolution transmission electron microscopy(HRTEM)were used to study the microscopic and nanoscopic structure of soot particles.The characteristics of the nano-structures such as the diameter of the soot primary particles,the radius of gyration of the soot agglomerate,the fractal dimension,the length and distortion of fringe under different working conditions were studied.The results show that from the upstream to the downstream of the flame,the diameter of the primary particles and the radius of gyration of the agglomerates decrease,the length of the fringe increases,the degree of distortion decreases,and the degree of graphitization of the primary particles increases,presenting a typical"core-shell"structure;as the amount of fuel injection decreases,the formation process of soot element particles is inhibited,the average diameter of the primary particles and the radius of gyration of the agglomerate decrease,the length of the fringe decreases,and the distortion increases.The degree of graphitization of particles decreases.With the decrease of oxygen concentration,the oxidation process of soot-based particles is inhibited.The average diameter of the primary particles and the radius of gyration of the agglomerates increase,and the length of the fringe decreases,and the distortion increases.The degree of graphitization of the elemental particles is lowered.