正庚烷/正丁醇扩散火焰中碳烟微观结构的演变
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摘要
基于层流扩散火焰研究了碳烟颗粒的形貌和纳米结构的演变过程.研究的燃料包括正庚烷、正丁醇以及二者的等体积混合物(H50B50).采用热泳探针法采样并使用透射电子显微镜TEM进行样本观测.总体来说,正丁醇火焰中产生的碳烟颗粒尺寸最小,数量也最少,其次是H50B50和正庚烷火焰;在碳烟发展过程中积聚颗粒的分形维数呈现单调递增的趋势.在碳烟生长阶段,微晶长度和曲率会减小,层间距会增大;随后,碳烟石墨化程度增大,微晶长度增大,微晶曲率和层间距减小;在碳烟发展后期,外层大量微晶被氧化,微晶曲率会增大.另外,正丁醇火焰尖端中成熟的碳烟具有最大的微晶长度和曲率以及最小的层间距.
The morphology and nanostructure of soot particles was investigated based on laminar diffusion flame. Fuels included n-heptane,n-butanol and a volumetric mixture of 50% n-heptane and 50% n-butanol(H50 B50). Thermophoretic sampling and transmission electron microscopy(TEM) were used to observe the samples. Overall,the n-butanol flame produced the smallest and fewest soot particles,followed by H50 B50 and n-heptane. The fractal dimension of aggregates continuously increased during soot development. In the process of soot growth,the fringes become shorter and less curved,and inter-fringe spacing increased. Subsequently,the degree of graphitization would increase;thus,the fringe length increased,while tortuosity and inter-fringe spacing decreased. In the final stage of soot development,most microcrystalline carbon layers in the outer shell were oxidized,which caused a sharp increase in tortuosity. In addition,for the mature soot near flame tips,particles in the n-butanol flame exhibited maximum fringe length and tortuosity with minimum inter-fringe spacing.
The morphology and nanostructure of soot particles was investigated based on laminar diffusion flame. Fuels included n-heptane,n-butanol and a volumetric mixture of 50% n-heptane and 50% n-butanol(H50 B50). Thermophoretic sampling and transmission electron microscopy(TEM) were used to observe the samples. Overall,the n-butanol flame produced the smallest and fewest soot particles,followed by H50 B50 and n-heptane. The fractal dimension of aggregates continuously increased during soot development. In the process of soot growth,the fringes become shorter and less curved,and inter-fringe spacing increased. Subsequently,the degree of graphitization would increase;thus,the fringe length increased,while tortuosity and inter-fringe spacing decreased. In the final stage of soot development,most microcrystalline carbon layers in the outer shell were oxidized,which caused a sharp increase in tortuosity. In addition,for the mature soot near flame tips,particles in the n-butanol flame exhibited maximum fringe length and tortuosity with minimum inter-fringe spacing.
引文
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[5]Wang H.Formation of nascent soot and other condensedphase materials in flames[J].Proceedings of the Combustion Institute,2011,33(1):41-67.
[6]Lee K O,Zhu J.Effects of exhaust system components on particulate morphology in a light-duty diesel engine[C]//SAE Technical Paper.Detroit,MI,USA,2005,2005-01-0184.
[7]Zhu J,Lee K O,Yozgatligil A,et al.Effects of engine operating conditions on morphology,microstructure,and fractal geometry of light-duty diesel engine particulates[J].Proceedings of the Combustion Institute,2005,30(2):2781-2789.
[8]Song J,Lee K O.Fuel property impacts on diesel particulate morphology,nanostructures,and NOx emissions[C]//SAE Technical Paper.Detroit,MI,USA,2007,2007-01-0129.
[9]Soewono A,Rogak S.Morphology and microstructure of engine-emitted particulates[C]//SAE Technical Paper.Detroit,MI,USA,2009,2009-01-1906.
[10]Kholghy M,Saffaripour M,Yip C,et al.The evolution of soot morphology in a laminar coflow diffusion flame of a surrogate for Jet A-1[J].Combustion and Flame,2013,160(10):2119-2130.
[11]Botero M L,Chen D,Gonzalez-Calera S,et al.HRTEM evaluation of soot particles produced by the non-premixed combustion of liquid fuels[J].Carbon,2016,96:459-473.
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[13]AlfèM,Apicella B,Barbella R,et al.Structureproperty relationship in nanostructures of young and mature soot in premixed flames[J].Proceedings of the Combustion Institute,2009,32(1):697-704.
[14]Atsumi S,Hanai T,Liao J C.Non-fermentative path ways for synthesis of branched-chain higher alcohols as biofuels[J].Nature,2008,451:86-89.
[15]Wang H,Reitz R D,Yao M,et al.Development of an n-heptane-n-butanol-PAH mechanism and its application for combustion and soot prediction[J].Combustion and Flame,2013,160(3):504-519.
[16]Megaridis C M,Dobbins R A.Morphological description of flame-generated materials[J].Combustion Science and Technology,1990,71(1/2/3):95-109.
[17]Brasil A M,Farias T L,Carvalho M G.A recipe for image characterization of fractal-like aggregates[J].Journal of Aerosol Science,1999,30(10):1379-1389.
[18]Vander Wal R L.Soot nanostructure:Definition,quantification and implications[C]//SAE Technical Paper.Detroit,MI,USA,2005,2005-01-0964.
[19]Zhang R,Kook S.Structural evolution of soot particles during diesel combustion in a single-cylinder light-duty engine[J].Combustion and Flame,2015,162(6):2720-2728.
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