Soot Reduction By Addition Of Dimethyl Carbonate In Diffusion Flames:Nanostructure And Reactivity Evidences

Oxygenated fuels represent an attractive alternative as additives for reducing soot emissions.Dimethyl carbonate(DMC)is the oxygenated compound,which is a good option to reduce soot,but the characteristics of soot produced from combustion of hydrocarbon fuels blended with DMC are still missing in details.The present research studied the nanostructure and reactivity of soot particles in ethylene/DMC normal and inverse diffusion flames,n-heptane/DMC inverse diffusion flames,isooctane/DMC inverse diffusion flames,and n-heptane/isooctane/DMC inverse diffusion flames.High resolution transmission electron microscopy(HRTEM),X-ray diffractometry(XRD),and thermogravimetric analysis(TGA)were used to analyze the nanostructure and reactivity of soot.This thesis focuses on the effects of DMC addition to the nanostructure and reactivity of soot particles collected from normal diffusion flame(NDF)and inverse diffusion flames(IDF).The diffusion flames included ethylene,n-heptane,and isooctane as the main fuels with or without DMC addition.In addition,this thesis also focuses on the relations of nanostructure and reactivity,and studies the differences of the nanostructure and reactivity of the soot particles from NDF which had passed through the oxidation zone and the soot particles from IDF collected without oxidation.For ethylene/DMC NDF and IDF,n-heptane/DMC IDF,and isooctane/DMC IDF,the results showed that DMC addition were effective to decrease the average weights of soot formed in flames.The results of HRTEM images showed that soot particles obtained with DMC addition were liquid-like material and tight bonding,and exhibited higher disorganized layers which are more reactive than the soot obtained without DMC addition.Furthermore,HRTEM was used to analyze soot fringe characteristics consisting of fringe tortuosity,fringe length,and fringe separation.XRD was used to crosscheck the results for fringe separation,which was consistent with HRTEM results.In addition,the mass loss curve of TGA experiments showed that DMC addition could enhance the reactivity of soot particles.The last part contains the nanostructure of soot particles and oxidative reactivity were studied in n-heptane/isooctane/DMC inverse diffusion flames,which consisted of three types of liquid fuels in the diffusion flames,and it found that DMC addition was effective in decreasing the weights of soot.However,the result of HRTEM without DMC addition had more liquid-like material and tighter bonding,and higher disorganized than the results of soot from n-heptane/isooctane/DMC IDF.The XRD results showed the degree of graphitization of soot was increased,which showed the differences in reactivity of soot particles.DMC addition have not improved the oxidation reactivity of soot particle in TGA results.For this reason,DMC addition enhance the oxidation reactivity of soot particle,and could help for soot reduction in ethylene/DMC NDF and IDF,n-heptane/DMC IDF,and isooctane/DMC IDF.In addition,DMC addition insignificantly affected to soot nanostructure and oxidative reactivity in n-heptane/isooctane/DMC inverse diffusion flames.However,the results of this thesis presented that DMC addition could totally help to decrease the soot formation.