柴油类燃料若干典型分子结构的燃烧反应动力学研究

发布时间：2018-04-30 09:05

  本文选题：柴油类替代燃料 + 多支链芳烃　； 参考：《中国科学技术大学》2016年博士论文

【摘要】：当前经济、社会发展所需的一次能源仍依托于化石燃料,它提供了全球能源总量约85%的比重。化石燃料的高效清洁燃烧以及代用燃料的发展始终是困扰人们的两大难题。这就要求研究者一方面深入理解化石燃料燃烧中的难点问题,另一方面完善对于生物燃料等代用燃料燃烧机理的认识。柴油中含有长链烷烃、环烷烃、单环芳烃和多环芳烃等多种有机成分。多支链单环芳烃是柴油中的重要组分类型,也通常被用作柴油替代燃料的代表性组分,其燃烧研究中不同支链位置和数量的动力学效应是需要重点解决的问题。而作为柴油代用燃料的生物柴油主要由酯类燃料构成,对于其特征基团酯基在燃烧中的转化机理也需要得到充分的认识。因此,本论文分别针对这两个问题,选取最简单的双支链芳烃一一二甲苯的三种同分异构体,以及最简单的三支链芳烃之一1,2,4-三甲苯,对不同支链位置和数量的多支链单环芳烃开展燃烧反应动力学实验和模型研究；并选取最简单的包含C2以上烷基基团的甲酯类燃料丙酸甲酯,研究酯基在甲酯类燃料分解中的作用。本论文的工作主要从两个方面展开。在实验方面,开展了流动反应器热解和低压层流预混火焰研究,利用同步辐射真空紫外光电离质谱技术对热解和火焰物种进行诊断,包括主要物种、稳定中间产物、自由基和多环芳烃。在热解中测得热解物种摩尔分数随温度变化的曲线,在火焰中测得火焰物种摩尔分数随火焰高度变化的曲线。在模型方面,构建了三种二甲苯燃料和1,2,4-三甲苯的燃烧反应动力学模型以及丙酸甲酯的热解反应动力学模型,并利用实验测量结果对模型进行了深入的验证。基于生成速率分析和灵敏性分析对关键物种和反应进行动力学分析,明确燃料的燃烧反应动力学特性。对于二甲苯体系,热解过程中燃料的单分子解离反应和自由基进攻反应是引发燃料初始分解的重要反应,其中以自由基进攻反应贡献最大。自由基进攻反应主要包括氢提取反应和本位加成反应。热解过程中自由基进攻以H进攻为主导。通过氢提取反应燃料会生成相应的二甲苯基,本位加成反应则会生成甲苯。邻二甲苯基和对二甲苯基可以通过单分子脱氢生成相应的二亚甲基苯,而间二甲苯基由于无法大量生成间二亚甲苯,只能通过环异构过程生成对二亚甲基苯。火焰中氢提取反应是二甲苯的主要初始消耗路径,由H和OH自由基进攻引发,可以发生在甲基位和苯环位,分别生成对应的二甲苯基和二甲基苯基。贫燃火焰中二甲苯基主要通过氧化反应消耗,进而生成苯和甲苯。富燃火焰中二甲苯基与热解过程中类似,主要是通过单分子解离反应消耗的。而对于间二甲苯基,氧化反应在富燃条件下仍具有一定贡献。芳烃生长路径在邻二甲苯和对二甲苯/间二甲苯的燃烧过程中有明显区别。邻二甲苯具有邻位结构,在茚和萘的生成过程中,邻位成环作用起到了极其重要的作用。在对二甲苯和间二甲苯体系中,fulvenallenyl((?))自由基是重要的芳烃生长前驱体之一,而该自由基主要是由二甲苯基的单分子解离反应引导生成fulvenallene((?)),并进一步通过脱氢或氢提取反应生成。在间二甲苯体系中,间二甲苯基无法大量生成二亚甲苯,造成间二甲苯基富集并向着其他反应通道进行分解。在此过程中造成芳烃生长前驱体之一的fulvenallenyl自由基大量生成,进而使得芳烃生长的反应流量增大,最终造成间二甲苯体系中芳烃生成趋势比对二甲苯体系更强。在1,2,4-三甲苯的热解和火焰中,燃料的主要消耗路径为自由基进攻反应,特别是H提取反应和本位加成反应。在低压热解中,燃料的单分子解离反应也占有一定比例。1,2,4-三甲苯涉及到邻-、间-、对-三个甲基位点的结构,其燃烧动力学也因此涉及到三个二甲苯的反应动力学。燃料初级分解过程产生了大量的二甲基苄基,在贫燃与富燃条件下的消耗路径不同,但都对后续小分子产物的生成具有重要意义。fulvenallenyl自由基是萘、菲等重要的PAH生成前驱体,主要由燃料相关路径生成,该路径已被实验证实。根据富燃火焰中m/z=105(对应于二甲苯基)的光电离效率曲线,可以发现二甲苯基主要由80%间二甲苯基和20%对二甲苯基组成,非常接近于模型的预测值(间二甲苯基：对二甲苯基=5：1)。Fulvenallenyl是间二甲苯基的后续产物之一,1,2,4-三甲苯中产生大量间二甲苯基验证了芳烃生长的路径。此外,茚主要来自于另一条与燃料直接相关的路径。对于多支链芳烃燃料的初始热解分解过程,单分子解离反应以脱氢反应为主,脱甲基反应贡献几乎可以忽略。双分子反应主要包括氢提取反应和本位加成反应,其中以氢提取反应为主导。并且随着甲级数量的增加,甲基位氢提取反应贡献也随之增加。此外,在三甲苯火焰中苯环位氢提取反应贡献可忽略。甲基位发生脱氢反应后生成的自由基是二甲苯和三甲苯分解过程中的最主要的中间物种,其中二甲苯生成二甲苯基,三甲苯分解生成二甲基苄基。对于1,2,4-三甲苯,三个甲基并不等价,不同甲基位的脱氢反应会生成不同二甲基苄基异构体。三甲苯比二甲苯多一个甲基,随着甲基数量的增多,相应的燃料初始脱氢自由基的单分子解离反应数量也随之增加。在丙酸甲酯的热解过程中,单分子解离反应、氢提取反应以及初始中间产物的后续分解反应对于燃料丙酸甲酯的分解意义重大。因此本工作中对这些反应路径进行了理论计算,并计算了其反应速率常数,用以建立更加准确的热解反应动力学模型。基于理论计算,发现了CH3CHCO和CH3OH两条新的生成通道,一条是直接通过四元环过渡态生成。另一条包括三个步骤,分别为H转移、H旋转和CH3OH消去。基于实验和理论计算,我们建立了一个包含98个物种和493个反应的丙酸甲酯热解反应动力学模型。该模型可以很好地模拟出大多数热解物种的摩尔分数曲线。丙酸甲酯的分解和其他热解产物的生成对初始反应的速率常数十分敏感。ROP分析显示三个单分子解离反应是丙酸甲酯的主要消耗反应,即MP=CH3+CH2COOCH3、MP=CH3+CH3CH2COO和MP=CH3CHCO+CH3OH。燃料中的酯基对于氧化产物的生成具有重要意义。
[Abstract]:In the current economy, the energy needed for social development is still dependent on fossil fuels, which provides a total of about 85% of the total energy in the world. The high efficiency and clean combustion of fossil fuels and the development of alternative fuels have always been the two difficult problems that perplex people. This requires researchers to understand the difficult problems in fossil fuel combustion, and the other one, the other one. There are many kinds of organic components such as long chain alkanes, naphthenic hydrocarbons, mono cyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons. Polybranched mono arene is an important component of diesel fuel and is usually used as a representative component of diesel fuel alternative fuels. The dynamic effect of placing and quantity is a key problem to be solved. And the biodiesel as a substitute fuel for diesel is mainly made up of ester fuel, and the transformation mechanism of its characteristic group ester in combustion must be fully understood. Therefore, this paper selects the simplest double branched aromatics one by one for these two problems. Three isomers of xylene and one of the simplest three branched aromatics, 1,2,4- three toluene, were used to conduct combustion kinetics experiments and model studies on multi branched chain mono cyclic aromatic hydrocarbons with different branched chain positions and numbers, and the most simple methyl methyl propionate, which contained the alkyl group above C2, was selected, and the ester group was studied in methyl ester combustion. The work of this paper is mainly carried out in two aspects. In the experiment, the pyrolysis of the flow reactor and the low-pressure laminar premixed flame are studied, and the pyrogenation and flame species are diagnosed by synchrotron vacuum ultraviolet photoionization mass spectrometry, including the main species, the stable intermediate products, the free radicals and polycyclic aromatic hydrocarbons. The curves of the molar fraction of the pyrolytic species with the temperature are measured in the pyrolysis, and the curves of the flame species mole fraction change with the flame height are measured in the flame. In the model, the kinetic model of the combustion reaction of three kinds of xylene fuel and 1,2,4- three toluene and the kinetic model of the pyrogenation of propionate are constructed, and the experiment is used for the experiment. Based on the generation rate analysis and sensitivity analysis, the kinetic characteristics of the key species and reactions are analyzed, and the kinetic characteristics of the fuel combustion reaction are determined. For the xylene system, the single molecular dissociation reaction and the self based attack reaction of the fuel during the pyrolysis process are the initial decomposition of the fuel. The free radical attack reaction mainly consists of the free radical attack reaction. The free radical attack reaction mainly includes the hydrogen extraction reaction and the standard addition reaction. The free radical attack is dominated by the H attack during the pyrolysis process. The corresponding dimethylbenzene can be generated by the hydrogen extraction reaction fuel, and the standard addition reaction will produce toluene. The adjacent two methylene and the two a will be formed. The phenyl group can dehydrogenate the corresponding two methylene benzene through a single molecule, while the two methylene can not produce a large number of two methylbenzene, and can only produce to two methylene benzene through the cyclic isomerization process. The hydrogen extraction reaction in the flame is the main initial consumption path of the xylene, which is induced by the H and OH radical attack, and can occur in methyl and benzene. The ring position produces corresponding dimethylbenzene and two methyl phenyl respectively. The two methylene in the lean combustion flame is mainly consumed by the oxidation reaction, and then produces benzene and toluene. The two methyl in the rich flame is similar to the pyrolysis process, mainly by the single molecule dissociation reaction. And for the two methylene, the oxidation reaction is still under the condition of rich combustion. There is a significant difference in the aromatics growth path in the combustion process of xylene and p-xylene / m xylene. The ortho dimethylbenzene has a neighborhood structure. In the formation of the nylene and naphthalene, the neighbouring ring formation plays an extremely important role. The fulvenallenyl ((?)) radical is heavy in the system of p-xylene and two toluene. One of the precursors of aromatics growth is required, and the free radical is guided by the two methylene single molecule dissociation reaction leading to fulvenallene ((?)) and further generated by dehydrogenation or hydrogen extraction. In the m xylene system, the two methylene can not produce a large amount of toluene, resulting in the enrichment of two methylene and the other reactions. In this process, the fulvenallenyl free radical of one of the precursors of aromatics growth is produced, and the flow rate of the aromatics growth is increased, and the aromatics generation trend in the xylene system is stronger than that of the p-xylene system. In the thermal solution and flame of 1,2,4- three toluene, the main consumption path of the fuel is The free radical attack reaction, especially the H extraction reaction and the standard addition reaction. In the low pressure pyrolysis, the single molecular dissociation reaction of the fuel also occupies a certain proportion of the.1,2,4- trimethyl benzene involving the adjacent, inter, and the structure of the three methyl sites, and its combustion kinetics also involves the reaction kinetics of the three xylene. The primary decomposition process of fuel is also involved. A large number of two methyl benzyl groups have been produced, which are different in the poor combustion and burning conditions, but are important for the generation of subsequent small molecular products..fulvenallenyl free radicals are important PAH precursors, such as naphthalene and phenanthrene, which are mainly generated by fuel related paths. The path has been proved by experiments. According to the m/z=105 in the burning flame, According to the photoionization efficiency curve of dimethylbenzene, it is found that the dimethylbenzene group is composed mainly of 80% two methylene groups and 20% dimethylbenzene groups, very close to the predicted value of the model (two methylene: p-xylene =5:1).Fulvenallenyl is one of the follow-up products of the two methylene benzyl, and a large number of dimethylbenzene is produced in 1,2,4- triphenyl. In addition to the path of aromatics growth, in addition, it mainly comes from another path that is directly related to fuel. For the initial decomposition process of multi branched aromatic hydrocarbon fuels, the single molecular dissociation reaction is mainly dehydrogenation reaction, and the contribution of demethylation reaction can almost be ignored. The main factors for the double molecular reaction include the hydrogen extraction reaction and the standard addition reaction, In addition, the contribution of the hydrogen extraction reaction of the benzene ring position in the trimethylamine flame is negligible. The free radical formed after the methyl dehydrogenation reaction is the most important intermediate species in the decomposition process of xylene and three toluene, The dimethylbenzene generates dimethylbenzene and three toluene is decomposed to produce two methyl benzyl. For 1,2,4- three toluene, three methyl groups are not equivalent, and the dehydrogenation reaction of different methyl sites will produce different two methyl benzyl isomers. Trimethylamine is more methyl than dimethylbenzene. With the increase of methyl number, the corresponding fuel dehydrogenated free radicals. The number of dissociation reactions also increased. During the pyrolysis of methyl propionate, the single molecule dissociation reaction, the hydrogen extraction reaction and the subsequent decomposition reaction of the initial intermediate products were of great significance for the decomposition of methyl propionate. Based on the theoretical calculation, two new generation channels of CH3CHCO and CH3OH are found. One is generated directly through the transition state of the four membered ring. The other includes three steps, namely, H transfer, H rotation and CH3OH elimination. Based on the experimental and theoretical calculations, we have established a total of 98 species and one of them. 493 reaction kinetic models of the pyrolysis of methyl propionate. This model can well simulate the mole fraction curve of most pyrolytic species. The decomposition of methyl propionate and the generation of other pyrolysis products are sensitive to the rate constant of the initial reaction..ROP analysis shows that the main consumption of three single molecule dissociation reactions is the main consumption of methyl propionate. Reaction, that is, the ester groups in MP=CH3+CH2COOCH3, MP=CH3+CH3CH2COO and MP=CH3CHCO+CH3OH. fuels are of great importance for the formation of oxidation products.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TK16
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本文编号：1823938