异辛烷/正庚烷/乙醇三组分燃料着火的化学动力学模型

提出一个包括异辛烷、正庚烷和乙醇的三组分燃料的着火动力学模型, 该机理包括50 个组分和193 个反应. 通过路径分析和灵敏度分析, 给出了基础燃料在高低温条件下的不同反应路径和影响氧化过程的重要基元反应. 该机理预测的单组分(异辛烷、正庚烷、乙醇)燃料、双组分基础燃料和三组分燃料的点火延迟时间与实验值有很高一致性. 本文机理包含较少的组分数与反应数, 因而可适用汽油掺烧乙醇的多维计算流体动力学(CFD)数值模拟.     

掺混含氧燃料的柴油替代物部分预混火焰中多环芳香烃的荧光光谱和碳烟浓度

为研究不同含氧燃料与柴油掺混后碳烟降低机理, 本文在自行设计的燃烧器上构建部分预混层流火焰, 采用甲苯和正庚烷混合物(T20, 20%(体积分数)甲苯、80%正庚烷)作为柴油替代物,并分别添加甲醇、乙醇、正丁醇、丁酸甲酯和2,5-二甲基呋喃(DMF), 且保证混合燃料的含氧量均为4%. 进而应用激光诱导荧光法和激光诱导炽光法分别测量不同混合燃料的火焰中多环芳香烃(PAHs)的荧光光谱和碳烟浓度. 结果表明: 通过PAHs的荧光光谱可测量不同燃料火焰中PAHs的生成和增长历程. 四环芳香烃(A4)的生成氧化规律和碳烟基本一致, 说明通过分析A4变化可以预测碳烟变化. 添加含氧燃料后, T20燃料中甲苯含量降低是导致PAHs的荧光光谱强度降低和碳烟生成量减少的主要原因; 同时不同含氧燃料本身对多环芳香烃的生成贡献能力也是影响PAHs的荧光强度和碳烟生成的重要原因. 含氧量相当时, 掺混正丁醇后PAHs的荧光光谱强度和碳烟浓度比添加甲醇、乙醇、丁酸甲酯和DMF这四种含氧燃料的更低. 因此从含氧燃料结构来讲, 正丁醇掺混入T20燃料中降低PAHs和碳烟作用最显著.     

RP-3航空煤油替代燃料及其化学反应动力学模型

本文提出了40%(摩尔分数, 下同)正癸烷、42%正十二烷、13%乙基环己烷和5%对二甲苯的四组分RP-3 航空煤油替代燃料模型, 并通过实验充分验证了替代燃料模型与实际RP-3 航空煤油在理化特性上的相似性. 采用对冲火焰实验台架, 测量了RP-3航空煤油以及四组分替代燃料的层流火焰传播速度. 对比结果表明本文提出的替代燃料能够准确描述实际RP-3航空煤油的燃烧速率. 进一步发展了包含168组分、1089反应的半详细反应动力学模型, 验证结果表明本文机理能够准确预测RP-3航空煤油着火延迟时间和火焰传播速度.     

航空煤油替代燃料模型构建方法及HEF航空煤油替代燃料模型

本文在完善燃烧化学特性参数,发展更准确的混合物特性参数计算方法的基础上,提出一套完整的、精确的航煤替代燃料模型构建方法。并采用定容燃烧弹实验系统首次测量了初始温度420和460 K、压力0.1 MPa,实际HEF航煤以及代表性组分十氢萘的层流火焰传播速度,为本文发展和验证替代燃料模型提供充分的实验数据。依据该方法提出了摩尔分数为65%正十二烷、10%正十四烷、25%十氢萘三组分HEF航煤替代燃料模型。充分的的实验和计算结果验证表明,替代燃料模型与实际HEF航煤在物理特性和燃烧化学特性方面有很高的相似性。本文提出的HEF航煤替代燃料模型和实验测量的层流火焰传播速度,为后续化学反应机理的发展与验证奠定了基础。     

适用于汽油参比燃料TRF的多环芳香烃生成机理

构造了一个包括287种组分和1569个反应的汽油参比燃料TRF(toluene reference fuel)燃烧过程中多环芳香烃(PAHs)生成机理的详细化学反应动力学模型,引入四种PAH生长路径将多环芳香烃的生成机理发展到芘A4(C20H12)水平,并通过对PAH产率的分析,指出乙炔(C2H2)、丙炔(C3H3)、乙烯基乙炔(C4H4)以及含有奇数碳原子的环戊二烯自由基(C5H5)和茚基(C9H7)等物质对PAHs生成和生长起到重要作用.该机理可以较准确计算基础燃料(PRF)和TRF火焰的着火延迟期、燃烧火焰中小分子(PAH前驱体C2H2、C3H4等)和PAHs的物质浓度.通过与实验数据的比较表明,该机理在不同温度、压力、化学计量比下具有较好的性能.由此分析,该机理对碳烟前驱物PAHs的预测性能是可靠的.     

正癸烷着火及燃烧的化学动力学模型

构建了一个包含46组分和167反应的描述正癸烷着火与燃烧过程的化学反应动力学机理模型, 该机理是在通过路径分析和灵敏度分析对Peters 机理(118组分和527反应)进行较大程度简化的基础上, 对低温着火和火焰传播速度影响较大的部分基元反应进行修正和改进后得到的. 与文献给出的实验结果对比表明, 该机理不仅比现有的机理具有较少的组分数和基元反应数, 而且能够更准确地预测正癸烷低温和高温条件下的着火延迟时间和火焰传播速度. 该机理为进一步实现总包简化机理与计算流体力学(CFD)的耦合计算奠定了基础.     

适用于HCCI燃烧的汽油替代燃料化学动力学简化模型

建立了一个适用于由正庚烷、异辛烷、甲苯和二异丁烯组成的汽油替代燃料均质压燃着火(HCCI)燃烧过程的简化机理模型, 包含103 种组分199 个反应. 二异丁烯主要通过燃料的脱氧反应消耗掉, 生成三种同分异构体, JC₈H₁₅-A、JC₈H₁₅-B和JC₈H₁₅-D; 燃料的分解反应也是二异丁烯的另外一条主要消耗路径, 生成两种重要的C₄产物, TC₄H₉和IC₄H₇. 这些产物是CH₂O的主要来源. 甲苯掺比燃料(TRF)机理主要是基于Andrae 等建立的TRF半详细机理, 甲苯和二异丁烯子机理是通过路径分析和敏感性分析得到. 简化机理能够很好地模拟激波管里的着火延迟和HCCI发动机实验, 由此可知, 本文提出的简化机理用来模拟HCCI燃烧是可靠的.     

低温燃料化学特性对湍流预混火焰传播的影响

大分子碳氢燃料的低温化学反应及两阶段点火特性会显著影响火焰的分区及燃烧情况。本文采用数值模拟的方法探究了正庚烷/空气预混混合气在RATS燃具上的湍流火焰传播,与试验结果具有一致性。模拟使用的是44种物质,112步的正庚烷简化动力学机理。使用Open FOAM的reacting Foam求解器建立了简化模拟流道及出口的三维模型,模拟了在大气环境下,初始反应温度450–700 K、入口速度6 m·s~(-1)与10 m·s~(-1)、焰前流动滞留时间100 ms及60 ms、当量比φ=0.6的正庚烷/空气混合气湍流火焰燃烧情况。结果发现,标准化湍流燃烧速度与混合气初始温度以及流动滞留时间有关。在低温点火阶段,正庚烷氧化程度受到初始温度与速度的影响,燃料分解并在预热区中产生大量中间物质如CH_2O,继而会影响湍流火焰燃烧速度。随着初始反应温度的升高,湍流燃烧火焰逐渐由化学反应冻结区过渡到低温点火区;温度超过一定数值后,燃料不再发生低温反应,此时燃烧位于高温点火区域。     

正癸烷热解的小规模化学动力学机理模型

正癸烷是目前常用的吸热型燃料的替代组分, 但是其热解机理的研究迄今还很少, 且现有的少数几个机理由于规模庞大使用不便. 本文首先构建了一个包含33种组分和75个基元反应的正癸烷热解动力学机理模型(Mech33); 随后, 在该机理的基础上进一步通过灵敏度分析得到影响主要热裂解组分生成的速率控制步, 并采用局部平衡和稳态假设对Mech33机理简化得到了规模更小的、仅包含22种组分和59步反应动力学机理模型(Mech22). 在较宽的温度和压力范围内对流动反应器及激波管中正癸烷热解过程进行了数值模拟, 并与实验数据进行了对比, 结果表明, Mech33和Mech22两个动力学机理模型都能够很好地描述正癸烷热裂解过程,并准确预测主要热裂解产物的浓度分布, 为进一步实现化学反应与计算流体力学(CFD)耦合的工程计算提供了有价值的动力学机理模型.     

RP-3航空煤油碳烟机理的构建与验证

燃料燃烧过程中形成的碳烟颗粒是航空发动机中污染物排放的主要成分。RP-3航空煤油作为我国最常用的航空燃料,从微观机理层次研究其碳烟机理对于发动机的污染物减排具有重要意义。本文基于RP-3的三组分替代燃料模型(质量分数为73.0%的正十二烷、14.7%的1,3,5-三甲基环己烷和12.3%的正丙基苯)构建了描述碳烟生成的详细燃烧机理模型,其中包括关键的链烷烃、环烷烃以及芳香烃的多环芳烃(PAHs)生成路径。该机理在多个工况条件下对高温点火延迟时间,层流火焰速度的预测与实验结果符合。碳烟产率的模拟结果表明,该机理能准确再现碳烟的生成。基于该机理对碳烟生成过程中起到关键成核作用的多环芳烃物种芘(A4)进行了敏感性分析,结果表明含有苯环的正丙基苯通过自身裂解产生苯自由基的反应显著促进A4的生成。反应路径分析结果表明在燃烧的不同阶段形成PAHs的各个反应的通量占比有差别,反应前期PAHs的生成主要来源于苯自由基的加成反应过程,而后期主要来源于小分子C₂、C₃、C₄等自由基的加成反应过程。     

Construction of a Chemical Kinetic Model of Five-Component Gasoline Surrogates under Lean Conditions

The requirements for improving the efficiency of internal combustion engines and reducing emissions have promoted the development of new combustion technologies under extreme operating conditions (e.g., lean combustion), and the ignition and combustion characteristics of fuels are increasingly becoming important. A chemical kinetic reduced mechanism consisting of 115 species and 414 elementary reactions is developed for the prediction of ignition and combustion behaviors of gasoline surrogate fuels composed of five components, namely, isooctane, n-heptane, toluene, diisobutylene, and cyclohexane (CHX). The CHX sub-mechanism is obtained by simplifying the JetSurF2.0 mechanism using direct relationship graph error propagating, rate of production analysis, and temperature sensitivity analysis and CHX is mainly consumed through ring-opening reactions, continuous dehydrogenation, and oxygenation reactions. In addition, kinetic parameter corrections were made for key reactions R14 and R391 based on the accuracy of the ignition delay time and laminar flame velocity predictions. Under a wide range of conditions, the mechanism’s ignition delay time, laminar flame speed, and the experimental and calculated results of multi-component gasoline surrogate fuel and real gasoline are compared. The proposed mechanism can accurately reproduce the combustion and oxidation of each component of the gasoline-surrogate fuel mixture and real gasoline.     

Unraveling chemical structure of laminar premixed tetralin flames at low pressure with photoionization mass spectrometry and kinetic modeling

This work reports an investigation on laminar premixed flames of tetralin at 30 Torr and equivalence ratios of 0.7 and 1.7. Measurements of the chemical structure including identification and mole fraction measurements of free radicals, isomers, and polycyclic aromatic hydrocarbons (PAHs) were performed using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV‐PIMS). A kinetic model with 296 species and 1 577 reactions was developed and validated against the flame chemical structure data measured in this work. Modeling analysis reveals the key reaction pathways in tetralin decomposition and PAHs formation. The H‐atom abstraction reactions by H, O, and OH are found to control the consumption of tetralin in the lean flame, while those by H play the dominant role in the rich flame. Indene and naphthalene have very high concentration levels in the rich tetralin flame due to the existence of direct formation pathways from the decomposition of tetralin. The two bicyclic PAHs and their radicals play significant roles in the PAHs growth process of tetralin combustion, which results in the high sooting tendency of tetralin compared to those of alkylbenzenes with smaller or same carbon atom numbers.     

A comprehensive and compact n-heptane oxidation model derived using chemical lumping

A detailed reaction mechanism for n-heptane oxidation has been compiled and subsequently simplified. The model is based on a kinetic model for C1-C4 fuel oxidation of Hoyermann et al. [Phys. Chem. Chem. Phys., 2004, 6, 3824] and a detailed mechanism for n-heptane oxidation developed by Curran et al. [Combust. Flame, 1998, 114, 149]. The generated mechanism is kept compact by limiting the application of the low temperature oxidation pathways to the fuel molecule. The first reaction steps and the complex low temperature paths in the oxidation process have been simplified and reorganized by linear chemical lumping. The reported procedure allows a decrease in number of species and reactions with only a minor loss of model accuracy. The simplified model is of very compact size and gives an advantageous starting point for further model reduction. By this chemically lumped general mechanism without further adjustments the large set of experimental data for the high and low temperature oxidation (ignition delay times, species concentration profiles, heat release and engine pressure profiles, flame speeds and flame structure data) for conditions ranging from very low to high temperatures (550-2300 K), very lean to extremely fuel rich (0.22 < phi < 3) mixtures and pressures between 1 and 42 bar is consistently described providing a basis for reliable predictions for future applications, (i) building reaction mechanisms for similar but chemically more complex fuels (e.g. iso-octane, n-decane,...) and (ii) calculating complex flow fields ("fluid dynamics") after further simplification with advanced reduction tools.     

Reduction of PAH and soot precursors in benzene flames by addition of ethanol

A one-dimensional premixed flame model (PREMIX) and schemes resulting from the merging of validated kinetic schemes for the oxidation of the components of the present mixtures (benzene and ethanol) were used to investigate the effect of oxygenated additives on aromatic species, which are known to be soot precursors, in fuel-rich benzene combustion. The specific flames were low-pressure (45 mbar), laminar, premixed flames at an equivalence ratio of 2.0. The blended fuels were formed by incrementally adding 4% wt of oxygen (ethanol) to the neat benzene flame and by keeping the inert mole fraction (argon) and the equivalence ratio constants. Special emphasis was directed toward the causes for the concentration-dependent influence of the blends on the amount of polycyclic aromatic hydrocarbons (PAHs) formed. The effects of oxygenate addition to the benzene base flame were seen to result in interesting differences, especially regarding trends to form PAH. The modeling results indicated that the concentration of acetylene and propargyl radicals, the main PAH precursors, as well as the PAH amounts were lower in the flame of the ethanol-benzene fuel mixture than in the pure benzene flame and that all of the formed PAHs were issued from the phenyl radical. Finally, the modeling results provided evidence that the PAH reduction was a result of simply replacing "sooting" benzene with "nonsooting" ethanol without influencing the combustion chemistry of the benzene.     

In situ direct sampling mass spectrometric study on formation of polycyclic aromatic hydrocarbons in toluene pyrolysis

The gas-phase reaction products of toluene pyrolysis with and without acetylene addition produced in a flow tube reactor at pressures of 8.15-15.11 Torr and temperatures of 1136-1507 K with constant residence time (0.56 s) have been detected in an in situ direct sampling mass spectrometric study by using a vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry technique. Those products range from methyl radical to large polycyclic aromatic hydrocarbons (PAHs) of mass 522 amu (C(42)H(18)) including smaller species, radicals, polyynes, and PAHs, together with ethynyl, methyl, and phenyl PAHs. On the basis of observed mass spectra, the chemical kinetic mechanisms of the formation of products are discussed. Especially, acetylene is mixed with toluene to understand the effect of the hydrogen abstraction and acetylene addition (HACA) mechanism on the formation pathways of products in toluene pyrolysis. The most prominent outputs of this work are the direct detection of large PAHs and new reaction pathways for the formation of PAHs with the major role of cyclopenta-fused radicals. The basis of this new reaction route is the appearance of different sequences of mass spectra that well explain the major role of aromatic radicals mainly cyclopenta fused radicals of PAHs resulting from their corresponding methyl PAHs, with active participation of c-C(5)H(5), C(6)H(5), C(6)H(5)CH(2) ,and C(9)H(7) in the formation of large PAHs. The role of the HACA only seemed important for the formation of stable condensed PAHs from unstable primary PAHs with zigzag structure (having triple fusing sites) in one step by ring growth with two carbon atoms.     

塑料焚烧过程中PAHs生成的动力学模拟

通过化学反应动力学机理,计算了塑料热解气在绝热燃烧反应体系中多环芳烃PAHs的生成情况。研究结果表明,在同样的反应温度下,随着燃烧摩尔比的增加,体系的反应不完全性加剧,同时PAHs生成峰值显著增加;在同样的燃烧摩尔比下,提高燃烧温度可以减小体系反应的不完全性,反应体系中PAHs生成峰值出现的时间均逐渐提前,同时其生成量也逐渐增大,随着反应温度的提高,生成PAHs的峰值幅度显著减小;在同样的反应体系温度和燃烧摩尔比下,纸张PAHs生成量比塑料和织物生成量小得多,而塑料和织物的PAHs生成量相当。