基于特征值分析的骨架机理获取方法

基于特征值分析法,建立了一套复杂化学反应动力学模型简化方法,并采用该方法对甲烷空气燃烧的详细化学反应动力学模型进行了简化.从GRI1.2得到了21个组分,83个反应的骨架机理.该机理与详细的GRI1.2机理和DRM19机理在不同化学计量比和不同压力下对比了点火延迟时间,结果表明简化机理能有效地再现详细反应动力学模型的反应机理,并具有更高的计算精度.从GRI3.0简化得到两种骨架机理分别为26个组分、120个反应和30个组分、140个反应.这两个机理都能很好地对火焰传播速度以及主要组分和NO浓度分布进行反应动力学模拟.     

基于特征值分析的正癸烷骨架和总包简化机理

使用基于特征值分析的骨架简化方法对由118 个组分和527 个反应构成的正癸烷详细机理进行了简化,获得了一个由70 个组分、327 个基元反应组成的骨架机理; 采用基于特征值分析的计算奇异摄动(CSP)简化方法对骨架机理进行进一步简化,得到一个38 组分、34 步的总包简化机理. 通过对简化机理、骨架机理和详细机理的对比发现,简化机理和骨架机理能够很好地再现详细机理的特性,并能够描述正癸烷的主要燃烧特性,为进一步实现耦合化学反应动力学与流体力学的工程计算,提高计算效率提供了可用的燃烧模型.     

Systematic procedure for reduction of kinetic mechanisms of complex chemical processes and its software implementation

Feasibility of multidimensional hydrodynamic modeling depends critically on the availability of accurate reduced kinetic mechanisms of physical and chemical processes taking place in the system. Such mechanisms should describe the processes under consideration within a specified error tolerance in the range of initial conditions of interest while keeping the number of species and reactions as small as possible. We have developed an advanced tool for reduction of detailed kinetic mechanisms with a minimal human effort. The tool includes 10 reduction and 2 analysis methods which are based on the results of zero-dimensional modeling. The methods can be combined and applied in sequence. The reduction tool has been implemented as a part the Chemical Workbench computational package and has been tested for a number of large kinetic mechanisms of gas-phase processes. Using this tool, we reduced the mechanism of tar gasification from 177 species and 879 reversible reactions to only 83 species and 278 reactions, while the mechanism of methane combustion initially involving 127 species and 1,206 reactions was reduced to 42 species and 173 reactions.     

Derivation of a quantitative minimal model from a detailed elementary-step mechanism supported by mathematical coupling analysis

Accurate experimental data increasingly allow the development of detailed elementary-step mechanisms for complex chemical and biochemical reaction systems. Model reduction techniques are widely applied to obtain representations in lower-dimensional phase space which are more suitable for mathematical analysis, efficient numerical simulation, and model-based control tasks. Here, we exploit a recently implemented numerical algorithm for error-controlled computation of the minimum dimension required for a still accurate reduced mechanism based on automatic time scale decomposition and relaxation of fast modes. We determine species contributions to the active (slow) dynamical modes of the reaction system and exploit this information in combination with quasi-steady-state and partial-equilibrium approximations for explicit model reduction of a novel detailed chemical mechanism for the Ru-catalyzed light-sensitive Belousov-Zhabotinsky reaction. The existence of a minimum dimension of seven is demonstrated to be mandatory for the reduced model to show good quantitative consistency with the full model in numerical simulations. We derive such a maximally reduced seven-variable model from the detailed elementary-step mechanism and demonstrate that it reproduces quantitatively accurately the dynamical features of the full model within a given accuracy tolerance.     

C1-C2燃料燃烧机理的框架简化

采用六种直接关系图类（DRG）方法对包含253个物种和1542个反应的AramcoMech 1.3机理进行简化,并通过对所得到的六种简化机理取交集,最终得到包含81个物种和497个反应的框架机理。所得81个物种框架机理的点火延迟时间最大误差与其简化方法得到的框架机理最大误差相比并没有显著增加;这表明从不同简化方法的框架机理结果取交集可以有效去除冗余物种。基于81个物种框架机理模拟的双组分混合燃料的点火延迟时间与详细机理机理结果吻合很好。同时该框架机理在不同反应器中的模拟结果验证了温度、物种浓度分布和火焰等燃烧特性。元素流动分析结果表明,81个物种框架机理精确地再现了详细机理的燃烧反应路径。保留了详细机理的所有重要反应路径和层级结构,能够很好地再现C₁-C₂燃料的各种燃烧特性。因此,基于该81个物种框架机理可作为核心机理用于发展大分子烃类或含氧燃料的燃烧机理。     

庚酸甲酯高温燃烧化学动力学机理的系统简化和分析

采用详细化学反应动力学机理的系统简化方法, 对庚酸甲酯高温燃烧化学动力学机理进行了系统简化. 首先采用两步直接关系图法(Directed relation graph method, DRG)和主成分分析(Principle component analysis, PCA)方法对由1087个物种、4592步可逆反应组成的庚酸甲酯燃烧的详细机理进行框架简化, 得到了包含108个物种, 547步基元反应的框架机理. 在此框架机理基础上, 进一步采用计算奇异值摄动法(Computational singular perturbation, CSP)对框架机理进行时间尺度分析, 再选取30个准稳态物种, 采用准稳态近似(Quasi steady state approximation, QSSA)方法构建了包含78个物种、74步总包反应的全局简化机理. 模拟结果表明, 在较宽的参数范围内, 框架机理和全局简化机理均能重现庚酸甲酯高温燃烧时的点火延迟、物种浓度分布和熄火等燃烧特性. 此外, 基于框架机理阐明了庚酸甲酯高温燃烧的反应路径和对点火有重要影响的基元反应. 与详细机理相比, 框架机理保留了良好的精确性和全局性, 可以很好地反映庚酸甲酯的燃烧特性, 有助于对生物柴油的燃烧过程的理解.     

正十二烷高温燃烧详细化学动力学机理的系统简化

采用详细化学反应动力学机理的系统简化方法, 以典型航空燃料的替代组分正十二烷为研究对象, 开展了正十二烷高温燃烧化学动力学机理的系统简化. 首先采用多步直接关系图法(DRG)和基于计算奇异值摄动法(CSP)重要性指标的反应移除方法对由1279个组分, 5056个基元反应组成的正十二烷燃烧详细机理进行框架简化, 得到了包含59 个组分, 222 个基元反应的框架机理; 进一步采用CSP对框架机理进行时间尺度分析, 选出了10个准稳态物种, 采用准稳态近似方法(QSSA)构建了包含49个组分的全局简化机理. 计算结果表明, 在较宽的参数范围内, 框架机理和全局简化机理均能够重现正十二烷详细机理在高温燃烧的点火延迟时间、熄火以及物种浓度分布等方面的模拟结果.     

Skeletal and reduced chemical mechanism for hydrogen fluoride chemical laser

The chemical kinetics of supersonic hydrogen fluoride (HF) chemical lasers determines combustion characteristics and output power. However, the inherent complexity of chemical reactions and complex structure still challenge the numerical simulations involving a comprehensive chemical mechanism. Therefore, a high fidelity and low computational consuming model is important for design purpose. This paper presents a strategy to generate a reduced mechanism for HF chemical lasers. Based on a detailed HF chemical mechanism consisting of 16 species and 153 elementary reactions, a specific skeletal mechanism including 11 species and 58 elementary reactions is generated. Finally, we obtain a further reduction mechanism including 11 species and 39 elementary reactions by combining sensitivity analysis and rate of production analysis. The computational cost for simulation of supersonic HF chemical lasers with the reduced mechanism is less than that with the detailed model. The principal contribution of the work is to provide a low computational consuming model.     

Fuel-specific influences on the composition of reaction intermediates in premixed flames of three C5H10O2 ester isomers

Measurements of the composition of reaction intermediates in low-pressure premixed flat flames of three simple esters, the methyl butanoate (MB), methyl isobutanoate (MIB), and ethyl propanoate (EP) isomers of C(5)H(10)O(2), enable further refinement and validation of a detailed chemical reaction mechanism originally developed in modeling studies of similar flames of methyl formate, methyl acetate, ethyl formate, and ethyl acetate. Photoionization mass spectrometry (PIMS), using monochromated synchrotron radiation, reveals significant differences in the compositions of key reaction intermediates between flames of the MB, MIB, and EP isomers studied under identical flame conditions. Detailed kinetic modeling describes how these differences are related to molecular structures of each of these isomers, leading to unique fuel destruction pathways. Despite the simple structures of these small esters, they contain structural functional groups expected to account for fuel-specific effects observed in the combustion of practical biodiesel fuels. The good agreement between experimental measurements and detailed reaction mechanisms applicable to these simple esters demonstrates that major features of each flame can be predicted with reasonable accuracy by building a hierarchical reaction mechanism based on three factors: (1) unimolecular decomposition of the fuel, especially by complex bond fission; (2) H-atom abstraction reactions followed by β-scission of the resulting radicals, leading to nearly all of the intermediate species observed in each flame; (3) the rates of H-atom abstraction reactions for each alkoxy or alkyl group (i.e., methoxy, ethoxy, methyl, ethyl, propyl) are effectively the same as in other ester fuels with the same structural groups.     

Extracting the mechanisms and kinetic models of complex reactions from atomistic simulation data

Determining reaction mechanisms and kinetic models, which can be used for chemical reaction engineering and design, from atomistic simulation is highly challenging. In this study, we develop a novel methodology to solve this problem. Our approach has three components: (1) a procedure for precisely identifying chemical species and elementary reactions and statistically calculating the reaction rate constants; (2) a reduction method to simplify the complex reaction network into a skeletal network which can be used directly for kinetic modeling; and (3) a deterministic method for validating the derived full and skeletal kinetic models. The methodology is demonstrated by analyzing simulation data of hydrogen combustion. The full reaction network comprises 69 species and 256 reactions, which is reduced into a skeletal network of 9 species and 30 reactions. The kinetic models of both the full and skeletal networks represent the simulation data well. In addition, the essential elementary reactions and their rate constants agree favorably with those obtained experimentally. © 2019 Wiley Periodicals, Inc.     

Development and testing of a comprehensive chemical mechanism for the oxidation of methane

A comprehensive chemical mechanism to describe the oxidation of methane has been developed, consisting of 351 irreversible reactions of 37 species. The mechanism also accounts for the oxidation kinetics of hydrogen, carbon monoxide, ethane, and ethene in flames and homogeneous ignition systems in a wide concentration range. It has been tested against a variety of experimental measurements of laminar flame velocities, laminar flame species profiles, and ignition delay times. The highest sensitivity reactions of the mechanism are discussed in detail and compared with the same reactions in the GRI, Chevalier, and Konnov mechanisms. Similarities and differences of the four mechanisms are discussed. The mechanism is available on the Internet as a fully documented CHEMKIN data file at the address http://www.chem.leeds.ac.uk/Combustion/Combustion.html . © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 513–538, 2001     

Reduction of large detailed chemical kinetic mechanisms for autoignition using joint analyses of reaction rates and sensitivities

This study describes a new technique of reduction of detailed mechanisms for autoignition. It is based on two analysis methods. An analysis of reaction rates is coupled to an analysis of reaction sensitivity for the detection of redundant reactions. Thresholds associated with the two analyses have a great influence on the size and efficiency of the reduced mechanism. Rules of selection of the thresholds are defined. The reduction technique has been successfully applied to detailed autoignition mechanisms of two reference hydrocarbons: n‐heptane and isooctane. The efficiency of the technique and the ability of the reduced mechanisms to reproduce well the results generated by the full mechanism are discussed. A speedup of calculations by a factor of 5.9 for n‐heptane mechanism and by a factor of 16.7 for isooctane mechanism is obtained without losing accuracy of the prediction of autoignition delay times and concentrations of intermediate species. © 2007 Wiley Periodicals, Inc. 39: 181–196, 2007     

燃烧反应机理构建的极小反应网络方法 氢氧燃烧

基于化学同时平衡原理, 提出复杂反应体系的极小反应网络方法(MRN), 在指定中间物种数目条件下, 构建反应步数最小的详细燃烧反应机理. 确定了8个物种的氢氧燃烧的6个独立反应, 对缺乏动力学参数的独立反应进行组合替代, 反应速率常数采用Arrhenius双参数形式. 采用构建的9步反应氢氧燃烧机理(MRN-C0)进行了点火延迟时间和层流火焰速度的模拟.     

The invariant constrained equilibrium edge preimage curve method for the dimension reduction of chemical kinetics

This work addresses the construction and use of low-dimensional invariant manifolds to simplify complex chemical kinetics. Typically, chemical kinetic systems have a wide range of time scales. As a consequence, reaction trajectories rapidly approach a hierarchy of attracting manifolds of decreasing dimension in the full composition space. In previous research, several different methods have been proposed to identify these low-dimensional attracting manifolds. Here we propose a new method based on an invariant constrained equilibrium edge (ICE) manifold. This manifold (of dimension nr) is generated by the reaction trajectories emanating from its (nr-1)-dimensional edge, on which the composition is in a constrained equilibrium state. A reasonable choice of the nr represented variables (e.g., nr "major" species) ensures that there exists a unique point on the ICE manifold corresponding to each realizable value of the represented variables. The process of identifying this point is referred to as species reconstruction. A second contribution of this work is a local method of species reconstruction, called ICE-PIC, which is based on the ICE manifold and uses preimage curves (PICs). The ICE-PIC method is local in the sense that species reconstruction can be performed without generating the whole of the manifold (or a significant portion thereof). The ICE-PIC method is the first approach that locally determines points on a low-dimensional invariant manifold, and its application to high-dimensional chemical systems is straightforward. The "inputs" to the method are the detailed kinetic mechanism and the chosen reduced representation (e.g., some major species). The ICE-PIC method is illustrated and demonstrated using an idealized H2O system with six chemical species. It is then tested and compared to three other dimension-reduction methods for the test case of a one-dimensional premixed laminar flame of stoichiometric hydrogen/air, which is described by a detailed mechanism containing nine species and 21 reactions. It is shown that the error incurred by the ICE-PIC method with four represented species is small across the whole flame, even in the low temperature region.     

Benzene combustion: A detailed chemical kinetic modeling in laminar flames conditions

Models resulting from the merging of validated kinetic schemes were used to compile a new detailed mechanism for benzene combustion in laminar flames. The proposed model, featuring 215 species and 1313 reactions, has been validated using fuel-rich, low-pressure, premixed benzene-oxygen-argon flames available in the literature. Good agreement between simulated and experimental data is achieved for the major reactants, intermediates, and products. However, computed maxima for some polyaromatic hydrocarbons were lower than experimental ones.     

土壤有机氯脱氯转化的界面交互反应*

有机氯杀虫剂、除草剂等难降解有机物是重要的土壤污染物。近年来,有机氯脱氯转化的界面过程已成为土壤环境科学的研究热点。本文综述了土壤有机氯脱氯转化的界面非生物过程、界面生物过程以及界面生物－非生物交互反应过程。界面脱氯转化过程与主要土壤化学过程、土壤根际过程相互关联,该过程中,铁物种循环与铁氧化物的异化还原溶解扮演了重要角色。     

高碳烃宽温度范围燃烧机理构建及动力学模拟

发动机中燃料点火特性以及燃烧能量的释放对于发动机设计具有非常重要的作用,为了提高燃料的燃烧效率以及减少燃料在燃烧过程中污染物的排放,基于反应动力学机理对燃料燃烧过程的模拟就显得十分必要。因此需要更加深入的认识碳氢燃料的燃烧机理,探索其在燃烧过程中十分复杂的化学反应网络。为了发展能够适用于实际燃料多工况条件(宽温度范围、宽压力范围和不同当量比)燃烧的燃烧机理,基于碳氢燃料机理自动生成程序ReaxGen构建了正癸烷燃烧详细机理(包含1499个物种,5713步反应)和正十一烷燃烧详细机理(包含1843个物种,6993步反应)。详细机理主要由小分子核心机理和高碳烃类(C5以上)机理两部分组成。为了验证机理的合理性与可靠性,本文对于高碳烃燃烧新机理在点火延时时间以及物种浓度曲线进行了动力学分析,并与实验数据及国内外同类机理进行了对比,结果表明本文提出的正癸烷和正十一烷燃烧新机理在比较宽泛的温度、压力和当量比条件下都具有较高的模拟精度,为发展精确航空煤油燃烧模型提供了基础数据。同时考虑到详细机理的复杂性以及机理分析的计算量大和时耗长,本文基于误差传播的直接关系图形(Directed Relation Graph with Error Propagation,DRGEP)方法简化得到的包含709组分2793反应的正癸烷和包含820组分3115反应的正十一烷简化机理,使用DRGEP方法时所采用的数据点选自压力范围从1.0×10~5 Pa到1.0×10~6Pa,当量比范围从0.5到2.0,初始温度范围从600到1400时恒压点火的模拟结果在点火延迟时间附近区域的抽样,同时在正癸烷机理简化中选取正癸烷、O_2和N_2作为初始预选组分,正十一烷的机理简化中主要选取正十一烷、O_2和N_2作为初始预选组分,得到的简化机理在比较宽泛的条件下的预测结果与详细机理吻合很好。最后结合敏感度分析方法分析了正癸烷和正十一烷的点火延迟敏感性,考察了机理中影响点火的关键反应。结果表明:这些机理能够合理描述正癸烷和正十一烷的自点火特性,在工程计算流体力学仿真设计中有很好的应用前景。     

RP-3高温氧化初始阶段反应机理的ReaxFF MD模拟

本文采用ReaxFF MD方法对一种较新的RP-3四组分替代燃料模型的高温氧化过程进行了研究。利用作者所在课题组研发的独特分析工具VARxMD,对燃烧过程中主要物种(燃料分子、O₂、C₂H₄、·CH₃)随时间和温度的演变规律及其化学反应进行了系统分析。ReaxFF MD模拟得到的燃料和氧气消耗量、乙烯和甲基自由基的生成量与相同温度和初始压力条件下CHEMKIN的计算结果处于同一量级,同时获得了详细的物质结构信息和反应列表。进一步对模拟得到的反应机理形式进行观察后发现,模拟获得的机理形式与文献中的描述一致。对燃料分子第一步反应数量的统计发现,其类型主要为攫氢反应和分子内断裂反应,且后者占主导;燃料分子第一步反应数量的统计也定性展现了不同燃烧条件下各类反应发生的可能性。对氧元素相关的反应分析发现,氧分子和C₁-C₃小分子发生的反应所占比例较大,能在一定程度上为机理简化提供有益线索。在对反应机理分析的基础上获得了RP-3四组分替代燃料体系高温氧化过程的化学反应网络。我们认为,ReaxFF MD反应分子动力学模拟、结合VARxMD对模拟结果深入分析的方法是有潜力系统认识燃料氧化反应机理的新方法,对构建燃料的燃烧反应机理库有一定的帮助。     

Dynamic reduction of a CH4/air chemical mechanism appropriate for investigating vortex–flame interactions

This paper describes two methods, piecewise reusable implementation of solution mapping (PRISM) and dynamic steady‐state approximation (DYSSA), in which chemistry is reduced dynamically to reduce the computational burden in combustion simulations. Each method utilizes the large range in species timescales to reduce the dimensionality to the number of species with slow timescales. The methods are applied within a framework that uses hypercubes to partition multidimensional chemical composition space, where each chemical species concentration, plus temperature, is represented by an axis in space. The dimensionality of the problem is reduced uniquely in each hypercube, but the dimensionality of chemical composition space is not reduced. The dimensionality reduction is dynamic and is different for different hypercubes, thereby escaping the restrictions of global methods in which reductions must be valid for all chemical mixtures. PRISM constructs polynomial equations in each hypercube, replacing the chemical kinetic ordinary differential equation (ODE) system with a set of quadratic polynomials with terms related to the number of species with slow timescales. Earlier versions of PRISM were applied to smaller chemical mechanisms and used all chemical species concentrations as terms. DYSSA is a dynamic treatment of the steady‐state approximation and uses the fast–slow timescale separation to determine the set of steady‐state species in each hypercube. A reduced number of chemical kinetic ODEs are integrated rather than the original full set. PRISM and DYSSA are evaluated for simulations of a pair of counterrotating vortices interacting with a premixed CH₄/air laminar flame. DYSSA is sufficiently accurate for use in combustion simulations, and when relative errors are less than 1.0%, speedups on the order of 3 are observed. PRISM does not perform as well as DYSSA with respect to accuracy and efficiency. Although the polynomial evaluation that replaces the ODE solver is sufficiently fast, polynomials are not reused sufficiently to enable their construction cost to be recovered. © 2007 Wiley Periodicals, Inc. 39: 204–220, 2007     

Experimental and modelling study of sulfur and nitrogen doped premixed methane flames at low pressure

Laser-induced fluorescence (LIF) has been used to observe NS and NO in methane/oxygen/argon laminar flames at low pressure doped with ammonia and sulfur dioxide. NS profiles as a function of height above the burner have been measured for rich flames. The effect of adding various amounts of sulfur dioxide on the observed NO in the burnt gas region has been investigated for a variety of stoichiometries. The experimental measurements have been compared with PREMIX simulations using a detailed elementary reaction mechanism for nitrogen- and sulfur-containing species in a methane flame. Sensitivity analysis has been employed to highlight the important reactions for NS, NO and SO2. The results demonstrate significant uncertainties in currently best available rate data for important reactions involving sulfur-containing species.