Studies On The Order Degree,Surface Functional Groups And Oxidation Reactivity Of Soot In A Diffusion Flame

As the continuous increase of the car ownership and the combustion of fossil fuel,the particle emission has drawn great attention in the world,so it is imperative to research on the particles.In recent years,the scholars at home and abroad have made significant progress in the research on the particles.For diesel engines,gas-solid combustion is very common,however,there is still no research involving the influence of gas-solid combustion on the particles.Additionally,the combustion process is so complex for diesel engines that it is tough to determine the influence of a single variable on the soot particles.Therefore,an n-heptane inverse diffusion flame was established combined with capillary sampling system.The evolution of order degree,surface functional groups and oxidation reactivity of soot particles was studied by characterizations including Raman spectrometer(RS),Fourier transform infrared spectrometer(FT-IR)and thermo gravimetric analyzer(TGA).And an aerosol generator RBG-1000 was employed to scatter the carbon into the flame to approximate and simplify the gas-solid combustion of diesel engines.The effect of carbon addition on the above-mentioned physicochemical properties of soot particles was studied.The major work and results of this dissertation are listed as follows:The values of AD1/AG increase along the flame,indicating the microstructure of soot particles becomes more ordered as the heights above the burner(HAB)increase.The values of AD1/AG of soot particles from the carbon-addition n-heptane diffusion flame are somewhat bigger than that of soot particles from the n-heptane diffusion flame,reflecting the carbon addition contributes to the more ordered soot particles.From the second-order Raman spectroscopy,it can be seen that the peaks become narrower as the HAB increases,that is to say,the microstructure of soot particles become more ordered,which is consistent with the first-order Raman spectroscopy.The relative contents of aliphatic C–H groups and aromatic C-H functional groups which were indicated by the normalized peak area ratio(AC-H/AC=C)decrease with the increase of HAB.The relative contents of carbonyl groups AC=O/AC=C also decrease with the rise of HAB.Furthermore,the relative contents of carbonyl groups AC=O/AC=C of soot particles from the carbon-addition n-heptane diffusion flame look smaller.The oxidation reactivity of soot particles in different conditions was studied by TGA.The results show that the corresponding thermo gravimetric curves move right as the increase of HAB,indicating that it is difficult for soot particles from the bigger HAB to oxidize.The values of onset temperature(Ti),maximum rate temperature(Tmax),burnout temperature(Th)and apparent activation energies(Ea)show the trend of rise as the increase of HAB.Additionally,the oxidation reactivity characteristic temperature and apparent activation energies of soot particles from the carbon-addition n-heptane diffusion flame are larger,showing that the carbon addition could contribute to the decrease of oxidation reactivity of soot particles.