Studies On The Morphology,Nanostructure And Oxidation Reactivity Of Soot In A C₂H₄/O₂/Ar Premixed Flame

Recently,soot particles generated by fossil fuel have caused severe harmfulness to atmospheric environment and human health,causing the government and the public pay more attention to soot particles generated by combustion sources.The formation mechanism and evolution process of soot particles in combustion process have presently become research focuses.In this study,the effect of combustion conditions on the micromorphology,nanostructure,degree of graphitization and oxidation reactivity of soot particles was studied.Experiments were performed in a burner-stabilized ethylene/oxygen /argon premixed flame,and the soot was collected by an in-situ capillary system and an thermophoretic sampling particle diagnostic system(TSPD),and analyzed using several advanced technologies,including transmission electron microscopy(TEM)?Raman Spectrometer(RS)and Thermo Gravimetric Analyzer(TGA).The major research results and achievements of this dissertation are listed as follows:The studies of morphology suggest that soot formation and evolution process can be divided into: nucleation,surface growth,agglomeration and oxidation stages in the burner-stabilized ethylene/oxygen /argon premixed flame.With the increase of HAB(height of burner),soot particles are evolved from the nascent soot into mature agglomerated soot.The fractal dimensions of agglomerates and the mean diameters of primary particles range from 1.36 to 2.03 and from 14.706 to 21.397 nm,respectively.Both of them gradually increase as the equivalence ratio and HAB increase.In addition,the distributions of primary particle size are unimodal,in the range of 8~29nm.The peaks of primary particle size distributions locate in 14~25nm,and show an increase as the equivalence ratio and HAB increase.The mean fringe length,fringe tortuosity and the fringe separation distance of soot in premixed flame are in ranges of 0.741~1.250 nm,1.385~1.491 and 0.348~0.390 nm,respectively.Together with the increase in equivalence ratio and HAB,the fringe length gradually increases,while the fringe separation distance and tortuosity decrease.The ratios of AD1/AG in soot Raman measurements are 1.82-2.76,and the peak area of D2 and D4 accounts for 14.78%~20.62% and 3.76%~7.51% of total peak area,respectively.As the equivalence ratio and HAB increase,AD1/AG gradually increases and the ratios of D2 and D4 peak area to the total peak area decrease.These results indicate that the graphitization degree of soot increases with the increases in equivalence ratio and HAB.Correspondingly,the soot in the premixed flame presents a decline in the structural disorder.The onset temperature,maximum rate temperature,burn-out temperature of soot are 480.43~552.75??566.57~656.33? and 632.37~725.83?,respectively.The apparent activation energies vary within 136.71~163.73 KJ/mol.As the equivalence ratio and HAB increase,the aforementioned temperatures and apparent activation energies exhibit gradual increases,indicating a decreased oxidation reactivity of soot.The results obtained from this study facilitate the understanding of formation mechanism and evolution process of soot particles,and assist in the reduction of soot particles emitted from diesel engines.