火焰中脂肪链结构生成的反应分子动力学模拟
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摘要
脂肪链结构对初始碳烟颗粒的形成起着重要作用.为研究碳烟颗粒中脂肪链结构的形成过程,通过Reax FF反应分子动力学的方法研究六苯并苯(C24H12)与气体小分子乙炔(C2H2)、乙烯(C2H4)在2 500 K下生成脂肪链结构的过程,讨论了气体小分子对碳烟中脂肪链结构形成的影响.结果表明,火焰中生成脂肪链结构的方式主要有两种:一是多环芳香烃(PAH)边界上的苯环断裂成链;二是气体小分子(C2H2和C2H4)在PAH边界上的生长成链.并且C2H2的存在更有助于第二种脂肪链结构的形成.
Aliphatic chains play an important role in the formation of soot particles. To investigate the formation of aliphatic chains in soot particles,a ReaxFF molecular dynamic(MD)simulation was used to uncover the process of forming aliphatic chains by circumcoronene(C24 H12)and gaseous molecules(C2 H2,C2 H4) at the temperature of2 500 K. Effects of different gaseous molecules were discussed during the process. Results show that there are two ways to generate aliphatic chains in flames:one is that polycyclic aromatic hydrocarbons(PAH)on the boundary of the benzene break into a chain;the other one is that the gaseous molecules grow into chains on the boundary of PAH.And the presence of C2 H2 is more conducive to the formation of the second aliphatic chains.
Aliphatic chains play an important role in the formation of soot particles. To investigate the formation of aliphatic chains in soot particles,a ReaxFF molecular dynamic(MD)simulation was used to uncover the process of forming aliphatic chains by circumcoronene(C24 H12)and gaseous molecules(C2 H2,C2 H4) at the temperature of2 500 K. Effects of different gaseous molecules were discussed during the process. Results show that there are two ways to generate aliphatic chains in flames:one is that polycyclic aromatic hydrocarbons(PAH)on the boundary of the benzene break into a chain;the other one is that the gaseous molecules grow into chains on the boundary of PAH.And the presence of C2 H2 is more conducive to the formation of the second aliphatic chains.
引文
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[4]Schuetz C A,Frenklach M.Nucleation of soot:Molecular dynamics simulations of pyrene dimerization[J].Proceedings of the Combustion Institute,2002,29(2):2307-2314.
[5]Omidvarborna H,Kumar A,Kim D S,et al.Recent studies on soot modeling for diesel combustion[J].Renew Sust Energ Rev,2015,48:635-647.
[6]Commodo M,De Falco G,Bruno A,et al.Physicochemical evolution of nascent soot particles in a laminar premixed flame:From nucleation to early growth[J].Combustion and Flame,2015,162(10):3854-3863.
[7]Wang L,Song J,Lv G,et al.Aliphatic C-H and oxygenated surface functional groups of diesel incylinder soot:Characterizations and impact on soot oxidation behavior[J].Proceedings of the Combustion Institute,2013,34(2):3099-3106.
[8]Cain J,Laskin A,Kholghy M R,et al.Molecular characterization of organic content of soot along the centerline of a coflow diffusion flame[J].Physical Chemistry Chemical Physics,2014,16(47):25862-25875.
[9]Cain J P,Gassman P L,Wang H,et al.Micro-FTIRstudy of soot chemical composition-evidence of aliphatic hydrocarbons on nascent soot surfaces[J].Physical Chemistry Chemical Physics,2010,12(20):5206-5218.
[10]Seung H C,Angela V.Peri-condensed aromatics with aliphatic chains as key intermediates for the nucleation of aromatic hydrocarbons[J].Proceedings of the Combustion Institute,2011,33(1):693-700.
[11]Paolo E,Angela V.Thermodynamics of poly-aromatic hydrocarbon clustering and the effects of substituted aliphatic chains[J].Proceedings of the Combustion Institute,2013,34(1):1837-1843.
[12]Van D A C T,Dasgupta S,Lorant F,et al.ReaxFF:A reactive force field for hydrocarbons[J].The Journal of Physical Chemistry A,2001,105(41):9396-9409.
[13]Happold J,Grotheer H H,Aigner M,et al.Soot precursors consisting of stacked pericondensed PAHs[C]//4th Ed,Anacapri:Proceedings of an International Workshop Held in Villa Orlandi,Karlsruhe University,2007:275-285.
[14]Michelsen H A.Probing soot formation,chemical and physical evolution,and oxidation:A review of in situ diagnostic techniques and needs[J].Proceeding of the Combustion Institute,2016,36(1):717-735.
[15]Payne M C,Teter M P,Allan D C,et al.Iterative minimization techniques for ab initio total-energy calculations:Molecular dynamics and conjugate gradients[J].Reviews of Modern Physics,1992,64(4):1045-1097.
[16]Aktulga H M,Fogarty J C,Pandit S A,et al.Parallel reactive molecular dynamics:Numerical methods and algorithmic techniques[J].Parallel Comput,2012,38(4):245-259.
[17]Strachan A,Van D A C T,Chakraborty D,et al.Shock waves in high-energy materials:The initial chemical events in nitramine RDX[J].Phys Rev Lett,2003,91(9):8301-8305.
[18]Strachan A,Kober E M,Van D A C T,et al.Thermal decomposition of RDX from reactive molecular dynamics[J].Journal of Chemical Physics,2005,122(5):1277-1291.
[19]Stoliarov S I,Westmoreland P R,Nyden M R,et al.Areactive molecular dynamics model of thermal decomposition in polymers 1:Poly(methyl methacrylate)[J].Polymer,2003,44(3):883-894.
[20]Humphrey W,Dalke A,Schulten K,et al.VMD:Visual molecular dynamics[J].Journal of Molecular Graphics,1996,14(1):33-38.
[21]Harris S J,Weiner A M,Ashcraft C C,et al.Soot particle inception kinetics in a premixed ethylene flame[J].Combustion and Flame,1986,64(1):65-81.