Study On The Three-dimensional Morphologic Structure Of Particulate Matter From A Diesel Engine

In this paper,the particulates of diesel exhaust were obtained under different working conditions and different particle sizes by using ZS195 single-cylinder engine bench tests and the MOUDI particulate sampling system.Soft X-ray micro imaging and 3D reconstruction were used to analyze 3D morphological characteristics and parameters of these obtained particulates under different working conditions(A/B)and different particle sizes(S6/S7).This research will be helpful to further understand the formation and evolution processes of the particulates of diesel exhaust.Micro orifice uniform deposit impactor(MOUDI)was used to sample the particulates of diesel exhaust under different working conditions and different particle sizes.These obtained particulates were analyzed and measured by using synchrotron soft X-ray microscopic imaging and 3D reconstruction system.The results show that the 3D morphologies of these particles are generally spherical or rice-granular shapes under low load,relatively dispersed chain structures under high load.And under low load,the accumulation of these particles is very obvious,and the outline of these particles is blurred,while the outline of these particles under high-load is clear;The 3D analysis software was selected to reconstruct the morphologic structure of soot aggregates and statistics the size distribution of these aggregates under different working conditions and different particle sizes.The results indicate that soot particles are mainly produced by the accumulation of dozens of soot aggregates with various shapes.In diesel engine exhaust gas,SOF and other substances are adsorbed on the surface of soot particles to form particulate matter,and the particle size and load have little influence on the main size distribution of soot aggregate size parameters;The 3D analysis software Amira was used to calculate and count the fractal dimension distribution of soot particles and aggregates of diesel engines under different working conditions(A/B)and different particle sizes(S6/S7).The results show that fractal dimension of these soot particles and aggregates both approximates to normal distribution under different working conditions(A/B)and different particle sizes(S6/S7).The fractal dimension of soot particles distributes between 1.6 and1.85,and that of soot aggregates distributes 1.65 and 1.85,and the value of fractal dimension of the soot particle is always less than that of the aggregate;The volume proportion of soot particles in diesel exhaust particles under different working conditions(A/B)and different particle sizes(S6/S7)was calculated and counted by the 3D analysis software Amira.The results indicate that the volume proportion of soot particle in the particulate matter approximates to normal distribution under different working conditions(A/B)and particle sizes(S6/S7)and distributes between 0.5 and 0.7;Finally,the object specific surface of soot particles and particulate matter was also calculated by the 3D analysis software Amira.Combined with the calculation,the effects of load conditions and particle sizes on the SOF accumulation degree of soot particles were analyzed.The results indicate that for the same load condition,the smaller the particle size is,the more serious the particle surface accumulation phenomenon is,and the stronger the SOF adsorption ability is.For low load condition with the same particle size class,particles are densely aggregated,and particle surface accumulation phenomenon is serious,particle SOF adsorption ability is stronger.