丁醇掺混的甲烷同轴扩散火焰的实验和动力学研究

发布时间：2018-01-04 22:01

本文关键词：丁醇掺混的甲烷同轴扩散火焰的实验和动力学研究　出处：《中国科学技术大学》2015年博士论文　论文类型：学位论文

【摘要】：随着人口和经济的增长,人类社会对于能源的需求也飞速增长,导致作为主要能源的石油和煤等化石燃料的急剧消耗。同时主要由碳氢燃料组成的化石燃料的燃烧会导致严重的大气污染问题,日益侵害着环境安全和人类健康。因此,为实现社会的可持续发展,高效清洁燃烧技术和可再生燃料的发展迫在眉睫。然而,虽然人类利用化石燃料的时间已达数千年之久,但对于其燃烧污染物生成机理的研究仍无法从根本上满足燃烧污染物防治要求。另一方面,生物质燃料是目前重要的可再生能源之一,多与化石燃料掺混应用于内燃机燃烧。丁醇与常用的乙醇相比具有更高的热值、更好的发动机兼容性和更加便利的存储条件,是极富潜力的新型生物质燃料。当前对生物质燃料排放的新型燃烧污染物及与碳氢燃料掺混后的燃烧特性的研究尚处初级阶段,难以满足生物质燃料的发展与应用需求。因此,亟需研究生物质燃料与碳氢燃料的掺混燃烧及其反应动力学机理,为工程燃烧应用提供理论指导。甲烷是清洁化石燃料天然气的主要组分,也是最常见、动力学模型发展最为成熟的碳氢模型燃料。因此本论文选取甲烷作为同轴扩散火焰的基础燃料,研究碳氢燃料燃烧中多环芳烃(PAH)和碳烟等燃烧污染物的形成机理,以及丁醇异构体的掺混对芳烃污染物产率的影响,特别着眼于实际燃烧中扩散效应和物质分布不均匀性引起的污染物形成机理的改变。同轴扩散火焰是一种非常接近实际燃烧状态的实验室火焰,耦合了物质扩散和化学反应对于火焰结构的双重影响,特别是易于形成多环芳烃和碳烟,是研究多环芳烃和碳烟形成机理的理想火焰。在实验研究方面,本工作于国际上首次将同步辐射真空紫外光电离质谱技术(SVUV-PIMS)应用于同轴扩散火焰结构诊断,研究了不同氮气稀释比例的常压甲烷扩散火焰,以及四种丁醇异构体以不同比例掺混的常压甲烷扩散火焰。实验采用石英探针对同轴扩散火焰进行取样,取样得到的燃烧产物由SVUV-PIMS技术进行定性分析和定量测量。实验中,通过扫描光电离质谱和光电离效(PIE)率谱,得到了燃烧物种的分子量和电离能信息,从而在同轴扩散火焰中鉴别出了数十种分子量介于2至240之间的燃烧物种。除燃料、氧化剂和稀释气体外,还包括主要燃烧产物(H2、H2O、CO和C02)、自由基、稳定的小分子中间体、单环芳烃(MAH)和多环芳烃。另外,通过在不同光子能量下扫描火焰的中心轴线位置,获得了这些燃烧物种的摩尔分数沿中心轴线方向的空间分布情况。在模型研究方面,本工作发展了一个全新的丁醇燃烧反应动力学模型,由甲烷核心机理、丁醇子机理和芳烃子机理构成。甲烷核心机理是在USC Mech Ⅱ机理的基础上,结合最新C0-C4核心机理的理论和模型成果进行深度发展而成的。丁醇子机理和芳烃子机理则是在本课题组之前的丁醇同分异构体燃烧反应动力学模型和芳烃燃烧反应动力学模型的基础上分别发展而成的,对芳烃子机理还进行了一定的精简,以确保数值模拟效率。本工作采用的模型研究思路是先利用甲烷和丁醇各自的基础燃烧实验数据进行模型验证,确保各部分子机理的准确性,再开展同轴扩散火焰数值模拟的策略。其中,两类燃料的理想反应器实验验证采用的是OpenSMOKE软件,而同轴扩散火焰的燃烧数值模拟采用的是国际上先进的laminarSMOKE软件。用于模型验证的甲烷和丁醇文献实验数据包括火焰传播速度以及流动管热解、射流搅拌反应器氧化、层流预混火焰和对冲扩散火焰中的物种浓度等。在本工作的同轴扩散火焰模拟工作中,还进一步对芳烃子机理进行了验证和发展。通过对模拟结果和实验结果进行对比,结合相关文献的研究成果,增加了必要的反应路径、剔除了不合理的反应路径、更正了不准确的速率常数,从而完善并优化了丁醇燃烧反应动力学模型。基于理想反应器实验模拟和同轴扩散火焰的数值模拟结果,本论文对甲烷的燃烧过程进行了详细的动力学分析。重点对同轴扩散火焰中燃料的分解路径、重要芳烃前驱体的生成与消耗路径、苯和典型多环芳烃的生成路径进行了深入的生成速率分析和敏感性分析。结果表明,在甲烷扩散火焰中心线上,甲烷主要分解产生甲基,由甲基的自复合反应及其产物后续的分解反应产生乙烷、乙烯等稳定的C2小分子中间体以及乙基、乙烯基等C2活泼自由基。它们再分解产生的乙炔会和甲基进行复合反应,并最终反应形成重要的芳烃前驱体——炔丙基,后者的自复合反应是形成苯的重要路径。在扩散火焰的芳烃生长过程中,苯和苯基是大多数芳烃物种生长的起点,特别是苄基和单环芳烃的生成直接依赖于苯基与C1-C2中间体的反应。火焰中的小分子中间体,如乙炔、丙炔、丁二烯以及炔丙基、乙烯基等自由基,与苯、苯基和苄基等的反应最终会形成双环芳烃,例如萘和茚主要由苯、苯基和苄基与C2-C3中间体反应得到。多环芳烃自由基,如茚基和萘基等在由双环芳烃向更大的多环芳烃的生长过程中起到重要的作用。与此同时,在甲烷扩散火焰中,随着燃料端氮气比例的增加,燃料稀释效应引起了火焰温度的下降,从而引起芳烃前驱体、苯和多环芳烃产量的明显下降。这些都在本论文的各个章节中进行了深入分析。根据甲烷扩散火焰中的经验,在甲烷掺混丁醇同分异构体扩散火焰中我们保持了在两种不同丁醇掺混比例条件下火焰碳流量的恒定,这使得火焰温度和主要产物的摩尔分数在两种情况下几乎完全一致,从而凸现出丁醇掺混比例提高所引起的燃烧中间体浓度的显著变化。芳烃的生成随着丁醇掺混比的提高体现出较强的规律性,苯、甲苯、茚、萘等芳烃的浓度随丁醇掺混比例的提高而不断提高。在甲烷及丁醇掺混的甲烷火焰中,多环芳烃的主要生成路径均是苯、苯基和苄基与小分子中间体之间的反应,即苯是这一系列火焰中芳烃生长过程的起点和最重要的多环芳烃前驱体。丁醇的添加对甲烷同轴扩散火焰中苯和多环芳烃的生成具有促进作用,并且随着丁醇异构体分子支链复杂程度的增加而加强。在火焰中丁醇主要通过单分子解离反应和由H原子或甲基进攻引发的H提取反应产生燃料分子自由基,后经β解离形成小分子碳氢或含氧化合物。这些中间体或继续分解或和甲基反应形成芳烃前驱体,从而影响芳烃在不同丁醇异构体掺混的火焰中的浓度。就C6以下碳氢中间体而言,丁醇同分异构体的添加对其主要分解产物浓度的影响最为明显,例如正丁醇对C2中间体影响巨大,而叔丁醇则主要影响C3和C4中间体。因为在丁醇掺混的甲烷火焰中,苯的生成路径存在着较大的共性,绝大部分来自于炔丙基和C3物种的复合反应,而叔丁醇和异丁醇这两种支链结构的丁醇异构体相比正丁醇和仲丁醇这两种直链结构的能够更直接有效的提供C3中间产物,因此在它们掺混的甲烷火焰中生成了更多的苯。此外,炔丙基和乙烯基乙炔复合生成的甲苯能分解成苄基,这是另一种重要的芳烃前驱体。仲丁醇和叔丁醇相比另外两种丁醇异构体更容易分解产生1,3-丁二烯和乙烯基乙炔等不饱和C4烃类。因此,它们各自比拥有相同碳链结构的另一种异构体更容易生成甲苯和苄基。同时,多环芳烃的生成依赖于苯、苯基和苄基与C1-C3等小分子中间产物的多步加成或复合反应,容易生成苯和甲苯的火焰更容易产生多环芳烃,这是丁醇掺混的同轴扩散火焰中芳烃生长路径的共同特点。所以最终我们在实验和数值模拟结果中一致发现芳烃生成浓度的趋势是：叔丁醇异丁醇仲丁醇正丁醇。
[Abstract]:With the development of economy and population, the human society is the rapid growth of the demand for energy, resulting in sharply as the main energy consumption of oil and coal and other fossil fuels. At the same time, mainly composed of hydrocarbon fuel in the combustion of fossil fuels will lead to serious air pollution problems, increasingly harming the environment and human health. Therefore, for realize the sustainable development of the society, the development of efficient and clean combustion technology and renewable fuels imminent. However, although the human use of fossil fuels has time for thousands of years, but the research on its combustion pollutant formation mechanism is still not fundamentally meet the requirements of prevention and control of combustion pollutants. On the other hand, biomass fuel is one of the most important renewable energy and fossil fuel combustion. Mixing for butanol and ethanol compared with common higher calorific value, better start Machine compatibility and more convenient storage conditions, is a new type of biomass fuel has the potential to study. The new combustion emissions of pollutants of the biomass fuels and hydrocarbon fuel mixed combustion characteristics is still in the primary stage, it is difficult to meet the development of biomass fuels and application. Therefore, an urgent need to study biomass fuels and hydrocarbon fuel the mixing and combustion reaction mechanism, to provide theoretical guidance for the engineering application of combustion. Methane is a major group of clean fossil fuel gas, which is the most common, the most mature model of hydrocarbon fuel based fuel dynamics model development. This paper selects the methane as coaxial diffusion flame, combustion of hydrocarbon fuel in polycyclic aromatic hydrocarbons (PAH) formation mechanism and soot combustion pollutants, and butanol isomers of the mixing effect on the yield of aromatic hydrocarbons, with particular emphasis on The actual combustion diffusion effect and the material caused by the uneven distribution of pollutant formation mechanism. The change of coaxial diffusion flame is a kind of very close to the actual laboratory flame combustion status, coupling material diffusion and chemical reaction double effects on flame structure, especially the easy formation of polycyclic aromatic hydrocarbons and soot, is an ideal flame formation mechanism research polycyclic aromatic hydrocarbons and soot.
In the experiment, the technique on ionization mass spectrometry for the first time the international synchrotron radiation vacuum ultraviolet light (SVUV-PIMS) applied to the coaxial diffusion flame diagnosis structure, atmospheric methane diffusion flame with different nitrogen dilution ratio of atmospheric methane, and four butanol isomers with different proportion of mixed diffusion flame experiment using quartz. Probe to sampling the coaxial diffusion flame, combustion product sampling by qualitative analysis and quantitative measurement by SVUV-PIMS technology. In the experiment, by scanning photoionization mass spectra and photoionization efficiency (PIE) spectrum, the combustion species of molecular weight and ionization energy information, resulting in the coaxial diffusion flame identified dozens of the molecular weight between 2 to 240 species combustion. In addition to fuel, oxidant and dilution gas, including main combustion products (H2, H2O, CO and C02), free radicals, small molecules in the stable Intermediates, mono cyclic aromatic hydrocarbons (MAH) and polycyclic aromatic hydrocarbons. In addition, the spatial distribution of mole fraction of these combustion species along the central axis is obtained by scanning the central axis of the flame at different photon energies.
In this model, we developed a new butanol combustion reaction kinetics model by methane core mechanism, form mechanism and mechanism of sub sub butanol aromatics. Methane core mechanism is based on USC Mech II mechanism, combined with the latest C0-C4 core mechanism theory and the model results are the depth of evolution. Butanol and aromatic sub sub mechanism is the foundation mechanism before the research group of the butanol isomers combustion reaction kinetics and aromatic hydrocarbon combustion reaction kinetics respectively on the development and mechanism of aromatic sub also carried out some simplification, to ensure the efficiency of the numerical simulation. The research ideas used in this model is the first use of methane and the butanol combustion experiment data to validate the model, to ensure the accuracy of each part of the sub mechanism, and then carry out numerical simulation of the diffusion flame in the coaxial strategy. Experiment two, ideal reactor fuel is used in OpenSMOKE software, and the coaxial diffusion flame combustion numerical simulation using the international advanced laminarSMOKE software for model validation. The methane and butanol experimental data including flame propagation velocity and flow tube pyrolysis, jet stirred reactor oxidation, laminar premixed flame and the species concentration in flame diffusion. In this work the coaxial diffusion flame simulation, further on the aromatic sub mechanism was verified and developed. Through the comparison of simulation results and experimental results, combined with the research results of related literature, increase the reaction path necessary, eliminating the unreasonable reaction path correct, rate constants are not accurate, so as to improve and optimize the butanol combustion reaction kinetics model.
The numerical simulation results of ideal reactor simulation experiment and coaxial diffusion flame based on the detailed analysis of the dynamics of the combustion process of methane decomposition. The key path of the coaxial diffusion flame fuel path, production and consumption of aromatics precursors, the generated path of benzene and polycyclic aromatic hydrocarbons are the typical formation rate analysis and the sensitivity of in-depth analysis. The results show that the methane diffusion flame center line, mainly due to decomposition of methyl methane, ethane produced by the decomposition reaction of composite reaction and its products following methyl, vinyl stable C2 small molecule intermediates and ethyl vinyl, C2 active radicals. They then decompose acetylene and methyl for the complex reaction of aromatic precursor and eventually formed by reaction of propargyl -- important, since the latter complex reaction is an important path to the formation of benzene in expanding. Aromatic powder flame growth process, benzene and phenyl is the starting point for most aromatic species growth, especially the formation of benzyl and monocyclic aromatic hydrocarbons depend directly on phenyl and C1-C2 intermediate reaction. Small molecule intermediates in the flame, such as acetylene, methylacetylene, butadiene and Que Bingji, vinyl and other free radicals, and benzene. The reaction of phenyl and benzyl will eventually form bicyclic aromatic hydrocarbons, such as naphthalene and indene obtained mainly by benzene, phenyl and benzyl and C2-C3 intermediates. Polycyclic aromatic hydrocarbon free radicals, such as indenyl and naphthyl in growth process by PAHs to polycyclic aromatic hydrocarbons in greater play an important role. At the same time, the methane the diffusion flame, with the increase of fuel nitrogen proportion end, fuel dilution effect caused by the decrease of flame temperature, causing the aromatic precursors, benzene and polycyclic aromatic hydrocarbons yield decreased significantly. These are the various An in-depth analysis is carried out in the chapter.
According to the experience of methane diffusion flame, mixed butanol isomers in a diffusion flame we kept under two different conditions of mixing ratio of butanol flame carbon flow constant in methane mixing, the mole fraction of the flame temperature and the main products in the two cases are almost identical, which highlights the significant content of butanol change the concentration of combustion intermediates caused by improving the mixing ratio. The formation of the aromatics with butanol mixed ratio increase reflects the strong regularity, benzene, toluene, naphthalene and other aromatic indene, with butanol mixed proportion and constantly improve. The methane and methane flame in butanol mixing, mainly generated the path of polycyclic aromatic hydrocarbons are benzene, between phenyl and benzyl with small molecular reaction intermediates, namely benzene is the starting point of growth process of a series of aromatic hydrocarbons in the flame and the most important PAHs precursor. The addition of butanol On the formation of methane CO diffusion benzene and polycyclic aromatic hydrocarbons in the flame has a promoting effect, and increases with the increasing of the molecular complexity of the butanol isomers branched. Butanol in flames by unimolecular dissociation reaction induced by H and atomic attack or methyl H extraction reaction to produce fuel radicals, after the formation of small beta dissociation molecular hydrocarbon or oxygen-containing compounds. These intermediates or continue the decomposition or reaction of methyl aromatics and the formation of the precursor, thus affecting the concentration of aromatic hydrocarbons in different butanol isomers mixing flame. C6 following hydrocarbon intermediates, butanol isomers of the effects on the main decomposition products of concentration is most obvious, for example n-butanol is the intermediate of C2 impact, and tert butyl alcohol mainly affects C3 and C4 intermediates. Because methane flame in butanol mixing in the path of benzene has a greater total Of complex reaction comes from the vast majority of propargyl and C3 species, and butanol isomers of branched chain structures of these two kinds of tert butyl alcohol and isobutyl alcohol compared to n-butanol and butanol these two kinds of straight chain structure more directly and effectively provide the intermediate product of C3, so the methane flame in their mixing in generation more benzene. In addition, propargyl and vinyl acetylene compound generated by toluene can be decomposed into benzyl radical, which is another important aromatic precursor. Butanol and tert butyl alcohol compared to the other two butanol isomers more easily decomposed into 1,3- butadiene and vinyl acetylene and other unsaturated hydrocarbons. Therefore C4 each of them, than the other isomers with the same carbon chain structure facilitates the formation of toluene and benzyl. At the same time, the PAHs formation depends on benzene, phenyl and benzyl C1-C3 and small molecule intermediates of multi-step addition or composite reaction, easy to A benzene and toluene flame more prone to polycyclic aromatic hydrocarbons, which is coaxial mixing diffusion characteristics of butanol aromatic growth path flame. So in the end we in the experimental and numerical simulation results consistently found that the concentration of aromatic trend: tert butyl alcohol butanol isobutanol n-butanol.

【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】：2015
【分类号】：TK16

【参考文献】