煤燃烧中HgCl转化为HgCl_2的反应机理研究

本文用量子化学从头计算MP2/SDD方法研究了煤燃烧过程中间产物HgCl与HCl、Cl2的反应机理,优化得到反应途径上的反应物、过渡态、中间体和产物的几何构型。用QCISD(T)方法计算能量,同时进行零点能校正,并以此能量计算活化能,同时计算反应热效应及熵变,采用经典过渡态理论得到反应速率常数。计算所得的反应速率常数与文献值吻合较好。     

十六烷酸甲酯氢提取反应速率常数研究

氢提取反应作为燃料消耗的主要反应路径在燃烧过程中占据非常重要的地位.本文采用一种基于能量的分块方法(GEBF)将CCSD(T)-F12a/cc-pVTZ应用到十六烷酸甲酯(C_(15)H_(31)COOCH_3)与氢原子发生的氢提取反应高精度能垒的计算中,并基于此分析了M06-2X/6-311++G(d,p)方法计算的反应能垒的精确性.然后采用过渡态理论计算反应速率常数,计算结果显示在C_(15)H_(31)COOCH_3+H体系中,靠近酯基的α位点的氢提取反应不再占据主导地位,氢提取反应倾向于发生在离酯基较远的亚甲基位点,而较难发生在靠近酯基的部分位点和两个甲基位点上。我们分析发现,大分子中数量众多的低频振动对于速率常数的计算有很大的影响,因此为了得到更精确的速率常数,应该将大分子的低频振动处理为分子内阻尼转动。     

2-糠酸甲酯与羟基反应动力学的理论研究

糠酸甲酯是随着2,5-呋喃二甲酸二甲酯新合成方法的发展而发展起来的一种新型可再生生物燃料. 本文用CCSD(T)/CBS//M062X/cc-pVTZ方法研究了糠酸甲酯与羟基自由基之间的势能面,包括夺氢反应和加成反应. 确定了异构化和分解反应生成的初级自由基. 结果表明,支链甲基上的夺氢反应是主要的反应通道,呋喃环上的OH加成具有明显的压力依赖性. 本文提出的速率系数为糠酸甲酯燃烧机理的改进提供了重要的动力学数据,为进一步研究实际燃料的燃烧过程奠定了良好的基础.     

锗烯与异氰酸多通道反应的理论计算

采用密度泛函理论B3LYP方法研究了单重态GeH₂与HNCO的反应机理.在B3LYP/6-311++G**水平上对反应物、中间体、过渡态进行了全几何参数优化,通过频率分析和内禀反应坐标（IRC）确定中间体和过渡态,用QCISD（T）/6-311++G**方法计算了各个驻点的单点能.计算表明单重态的锗烯与异氰酸的反应有抽提氧、插入N-H键、抽提亚氨基的反应路径.采用经Winger校正的Eyring过渡态理论分别计算了1个大气压、不同温度下反应势垒较低通道的热力学及动力学性质,结果表明插入N-H键反应（GeH₂+HNCO→IM7→TS6→P2）通道在温度400 K～1400 K内,有较高的平衡常数和反应速率常数,为主反应通道,主产物为GeH₃NCO.     

甲酸乙酯与羟基自由基氢提取反应速率常数的量化计算与激波管实验

针对甲酸乙酯（H（CO）OCH₂CH₃）与羟基自由基（OH）的反应动力学展开了理论与实验研究.在理论方面,首先通过量化计算得到了在M06-2x/ma-TZVP水平下准确的反应势能面,随后利用多结构-扭转（multi-stucture torsion MS-T）方法对转动非谐效应进行了研究,获得了非谐校正系数,最后基于传统过渡态理论并考虑Eckart隧穿效应获得了200~2 000 K温度范围的反应速率常数.在实验方面,开展了激波管实验来测定H（CO）OCH₂CH₃与OH的反应速率常数,基于激光吸收光谱技术探测OH自由基306.7 nm的吸收线,并对反射激波后高温反应过程的OH浓度变化进行测量,从而获得了900~1 321 K温度范围的反应速率常数,并论证了理论计算结果的合理性与准确性.      

吸气式高超声速飞行器机体/推进一体化内外流非定常耦合方法

基于吸气式高超声速飞行器机体/推进一体化的气动布局设计方式，文章提出了一种内外流一体化流场的耦合求解方法，其中燃烧室内流场采用考虑有限速率化学反应动力学模型的一维非稳态方法求解，进气道和尾喷管外流场采用二维CFD软件计算，进气道与燃烧室在耦合界面处通过一维平均方法实现静温、静压和Mach数等参数传递.并分别以日本国家航空与航天实验室（NAL）的氢燃料燃烧室模型作为内流场验证算例，以某典型高超声速飞行器一体化模型作为内外耦合流场验证算例.研究结果表明:有限速率化学反应准一维方法能较为准确地模拟燃烧室内燃烧流场，提出的内外流场耦合方法能够有效地计算出内外流耦合效应，计算后体压力分布与理论值较接近.该方法可为超燃冲压发动机的性能快速分析和吸气式高超声速飞行器机体/推进一体化的初步分析设计提供重要参考.      

SH（D）和OH（D）自由基基态的结构与势能函数

采用QCISD（T）/ 6-311++G（3df,2pd） 和QCISD/6-311++G（3df,2pd）方法计算优化了SH（D）和OH（D）自由基分子基态X²Π的分子结构和离解能.并采用最小二乘法拟合Murrell-Sorbie 函数得到了相应的势能函数,由此计算的振转常数与实验光谱数据符合得相当好. 关键词： SH和OH自由基分子 X²Π）')" href="#">基态（X²Π） Murrell - Sorbie函数 势能函数     

含铬废物焚烧中反应CrO2OH+O→CrOOH+O2动力学研究

含铬废物在高温下与空气中氧发生燃烧反应,形成多种铬的氧化物,不同价态铬氧化物的毒性有较大差异,其中六价铬剧毒具有极强的致癌作用.Kashireninov和Fontijn(1998)在B.B.Ebbinghaus(1993,1995)研究基础上,通过热力学平衡分析给出了Cr-O-H-Cl-C燃烧系统中可能的铬氧化化学反应.本文从量子化学角度研究了其中CrO2OH O→CrOOH O2反应机理.通过Gaussian 98软件在B3LYP/6-311 G(d,p)模型化学水平上,优化得到各反应物质的几何结构、内部反应路径及经过零点能校正后的各驻点能量.采用过渡态理论计算标题反应CrO2OH O→CrOOH O2在1.01325×105Pa下反应速率常数为k(T)=4.37×10-17Texp(-7641.17/T)cm3·mol-1·s-1.     

ONIOM方法计算胺和二芳基碳正离子的亲核反应的速率常数

利用第一性原理计算了胺和二芳基碳正离子的亲核反应的速率常数. 研究不同的溶剂化模型(PCM、CPCM和COSMORS)、不同类型的原子半径(UA0、UAKS、UAHF、Bondi和UFF)、以及一些单点能计算方法(B3LYP、B3P86、B3PW91、BHANDH、BMKPBEPBE、M06、MP2和ONIOM)在计算这类速率常数时的表现.通过比较速率常数的实验值和计算值,发现ONIOM(CCSD(T)/6-311++G(2df,2p):B3LYP/6-311++G(2df,2p))//B3LYP/6-31G(d)/PCM/UFF方法表现最好. 该方法随后被用于计算更多的胺和二芳基碳正离子的亲核反应的速率常数. 65个反应的速率常数的实验值和计算值之间表现出了相当好的相关性,这表明该方法适用于计算胺二芳基碳正离子的亲核反应的速率常数.     

基于欧拉喷雾与火焰面/反应进度变量湍流燃烧模型的PRF燃料喷雾燃烧模拟研究

在开源计算流体软件OpenFOAM环境下,将基于欧拉方法的Σ-Y喷雾模型与非稳态火焰面/反应进度变量湍流燃烧模型相耦合,发展用于高温高压环境中液体燃料喷雾湍流燃烧高精度计算模型,分别对非燃烧和燃烧工况下的五种典型参比燃料(Primary Reference Fuel,PRF)的燃油喷射雾化与湍流燃烧过程开展数值研究。结果表明：该新型耦合模型能够准确的预测PRF燃料的喷雾和着火燃烧特性;所开发的重构数值喷雾纹影图像和燃烧OH^*图像处理方法能够很好地捕捉到试验的滞燃期、火焰浮起长度及喷雾火焰结构;研究揭示了不同比例的PRF燃料对喷雾及着火燃烧过程的影响特性,为替代燃料在发动机上的高效应用提供了理论指导。     

Modelling biodiesel–diesel spray combustion using multicomponent vaporization coupled with detailed fuel chemistry and soot models

A multicomponent vaporization model is integrated with detailed fuel chemistry and soot models for simulating biodiesel–diesel spray combustion. Biodiesel, a fuel mixture comprised of fatty-acid methyl esters, is an attractive alternative to diesel fuel for use in compression-ignition engines. Accurately modelling of the spray, vaporization, and combustion of the fuel mixture is critical to predicting engine performance using biodiesel. In this study, a discrete-component vaporization model was developed to simulate the vaporization of biodiesel drops. The model can predict differences in the vaporization rates of different fuel components. The model was validated by use of experimental data of the measured biodiesel drop size history and spray penetration data obtained from a constant-volume chamber. Gas phase chemical reactions were simulated using a detailed reaction mechanism that also includes PAH reactions leading to the production of soot precursors. A phenomenological multi-step soot model was utilized to predict soot emissions from biodiesel–diesel combustion. The soot model considered various steps of soot formation and destruction, such as soot inception, surface growth, coagulation, and PAH condensation, as well as oxidation by oxygen and hydroxyl-containing molecules. The overall numerical model was validated with experimental data on flame structure and soot distributions obtained from a constant-volume chamber. The model was also applied to predict combustion, soot and NOx emissions from a diesel engine using different biodiesel–diesel blends. The engine simulation results were further analysed to determine the soot emissions characteristics by use of biodiesel–diesel fuels.     

Numerical simulation of turbulent combustion: Scientific challenges

Predictive simulation of engine combustion is key to understanding the underlying complicated physicochemical processes, improving engine performance, and reducing pollutant emissions. Critical issues as turbulence modeling, turbulence-chemistry interaction, and accommodation of detailed chemical kinetics in complex flows remain challenging and essential for high-fidelity combustion simulation. This paper reviews the current status of the state-of-the-art large eddy simulation (LES)/prob-ability density function (PDF)/detailed chemistry approach that can address the three challenging modelling issues. PDF as a subgrid model for LES is formulated and the hybrid mesh-particle method for LES/PDF simulations is described. Then the development need in micro-mixing models for the PDF simulations of turbulent premixed combustion is identified. Finally the different acceleration methods for detailed chemistry are reviewed and a combined strategy is proposed for further development.     

Acceleration of the chemistry solver for modeling DI engine combustion using dynamic adaptive chemistry (DAC) schemes

Acceleration of the chemistry solver for engine combustion is of much interest due to the fact that in practical engine simulations extensive computational time is spent solving the fuel oxidation and emission formation chemistry. A dynamic adaptive chemistry (DAC) scheme based on a directed relation graph error propagation (DRGEP) method has been applied to study homogeneous charge compression ignition (HCCI) engine combustion with detailed chemistry (over 500 species) previously using an R-value-based breadth-first search (RBFS) algorithm, which significantly reduced computational times (by as much as 30-fold). The present paper extends the use of this on-the-fly kinetic mechanism reduction scheme to model combustion in direct-injection (DI) engines. It was found that the DAC scheme becomes less efficient when applied to DI engine simulations using a kinetic mechanism of relatively small size and the accuracy of the original DAC scheme decreases for conventional non-premixed combustion engine. The present study also focuses on determination of search-initiating species, involvement of the NO_x chemistry, selection of a proper error tolerance, as well as treatment of the interaction of chemical heat release and the fuel spray. Both the DAC schemes were integrated into the ERC KIVA-3v2 code, and simulations were conducted to compare the two schemes. In general, the present DAC scheme has better efficiency and similar accuracy compared to the previous DAC scheme. The efficiency depends on the size of the chemical kinetics mechanism used and the engine operating conditions. For cases using a small n-heptane kinetic mechanism of 34 species, 30% of the computational time is saved, and 50% for a larger n-heptane kinetic mechanism of 61 species. The paper also demonstrates that by combining the present DAC scheme with an adaptive multi-grid chemistry (AMC) solver, it is feasible to simulate a direct-injection engine using a detailed n-heptane mechanism with 543 species with practical computer time.     

Experimental and kinetic modeling study of α-methylnaphthalene laminar flame speeds

α-Methylnaphthalene (AMN) is the primary reference bicyclic aromatic compound of diesel, and it is commonly used as a component of diesel, kerosene and jet-fuel surrogates formulated to describe real fuel combustion kinetics. However, few experimental data on neat AMN combustion are available in the literature. This work provides the first measurements of laminar flame speed profiles of AMN/air mixtures at 1 bar varying the initial temperature from 425 to 484 K, and equivalence ratio (φ) between 0.8 and 1.35 paving the way for the kinetic study of AMN combustion chemistry at high temperatures (>1800 K). The experimental data obtained in a spherical reactor are compared with kinetic model simulations. Specifically, the AMN kinetics is implemented from its analogous monocyclic aromatic compound, i.e., toluene, through the analogy and rate rule approach. This method allows to develop kinetic mechanisms of large species from the kinetics of smaller ones characterized by analogous chemical features, namely the aromaticity and the methyl functionality in the case of toluene and AMN. In doing so, it is possible to overcome the need of high-level electronic structure calculations for the evaluation of rate constants, as their computational cost increases exponentially with the number of heavy atoms of the selected species. To assess the validity of this approach, ab initio calculations are performed to derive the rate constants of the H-atom abstraction reactions by H, OH and CH₃ radicals from both toluene and AMN. The kinetic model obtained satisfactorily agrees with the measured laminar flame speed profiles. Sensitivity and flux analyses are performed to investigate similarities and differences between the main reaction channels of toluene and AMN combustion, with the former leading to ∼6 cm/s faster flame speed at almost identical conditions (P=1 bar, T∼425 K), as evidenced by both kinetic model simulations and experimental findings.     

Numerical simulation and validation of SI-CAI hybrid combustion in a CAI/HCCI gasoline engine

SI-CAI hybrid combustion, also known as spark-assisted compression ignition (SACI), is a promising concept to extend the operating range of CAI (Controlled Auto-Ignition) and achieve the smooth transition between spark ignition (SI) and CAI in the gasoline engine. In this study, a SI-CAI hybrid combustion model (HCM) has been constructed on the basis of the 3-Zones Extended Coherent Flame Model (ECFM3Z). An ignition model is included to initiate the ECFM3Z calculation and induce the flame propagation. In order to precisely depict the subsequent auto-ignition process of the unburned fuel and air mixture independently after the initiation of flame propagation, the tabulated chemistry concept is adopted to describe the auto-ignition chemistry. The methodology for extracting tabulated parameters from the chemical kinetics calculations is developed so that both cool flame reactions and main auto-ignition combustion can be well captured under a wider range of thermodynamic conditions. The SI-CAI hybrid combustion model (HCM) is then applied in the three-dimensional computational fluid dynamics (3-D CFD) engine simulation. The simulation results are compared with the experimental data obtained from a single cylinder VVA engine. The detailed analysis of the simulations demonstrates that the SI-CAI hybrid combustion process is characterised with the early flame propagation and subsequent multi-site auto-ignition around the main flame front, which is consistent with the optical results reported by other researchers. Besides, the systematic study of the in-cylinder condition reveals the influence mechanism of the early flame propagation on the subsequent auto-ignition.     

A theoretical kinetics study on low-temperature oxidation of n-C4H9 radicals

The low-temperature oxidation mechanism of n?butyl radicals (n-C₄H₉) has been investigated by high level quantum chemical calculations coupled with the Rice–Ramsperger–Kassel–Marcus/Master Equation (RRKM/ME) theory. The potential energy surfaces (PES) were explored at the QCISD(T)/CBS//B3LYP/6-311++G(d,p) level. The temperature- and pressure-dependent rate constants were computed and fitted in modified Arrhenius parameters. The major reaction channels were discussed to more deeply understand the competing relationships between chain branching, chain propagation and termination reactions. The results show that the 1,5 H-shift reaction is more competitive than the 1,6 H-shift and 1,4 H-shift for isomerization reactions of n?butyl peroxy radicals, and the concerted HO₂ elimination channel to form butene becomes more important at high temperatures. Furthermore, based on our calculations, a revised kinetic model was developed to describe n-butane oxidation. Good consistency between model predictions and experimental data was shown. This study enhances our understanding of the combustion mechanism of n-butane and can be used as a reliable reference for mechanistic understanding of larger alkanes.     

精确计算TATB分子间相互作用能并重新认识其作用本质

TATB炸药的钝感性质与其分子间强烈的相互作用密切相关，目前尚难以用实验方法直接准确地测定其分子间相互作用能。已发表的理论研究工作受当时计算方法和条件限制，计算结果误差较大、充满矛盾。本文用B3PW91-D3BJ/def2-TZVPP方法优化了TATB二聚体可能存在的六种构型的几何结构并作振动频率分析，发现仅有三种稳定构型，即氢键构型A，堆叠构型B和C，用MP2/def2-TZVPP方法重新优化了这三种构型的几何结构参数，并用于CCSD(T)/CBS方法计算，得到分子间相互作用能分别为A: -6.20，B: -15.45，C: -15.65 kcal/mol，CCSD(T)/CBS计算中发现构型B和C的高级校正项大约是分子间相互作用能的50%，是MP2方法不可能准确预测TATB二聚体堆叠构型分子间相互作用能的原因；本文还用新一代能量分解方法ALMO-EDA分析了TATB分子间相互作用本质，发现对于堆叠构型B和C，除了色散作用之外，静电吸引对决定TATB二聚体中的几何结构十分重要，TATB高能炸药良好的钝感性质起源于其分子间较强静电吸引的驱动和定向，使之形成稳定的堆叠结构，其稳定性来源于色散和静电的协同作用。     

A hybrid droplet vaporization-chemical surrogate approach for emulating vaporization,physical properties,and chemical combustion behavior of multicomponent fuels

The complex nature of multicomponent aviation fuels presents a daunting task for accurately simulating combustion behavior without incurring impractical computational costs. To reduce computation time, chemical fuel surrogates comprised of only a few species are used to emulate the combustion of complex pre-vaporized fuels. These surrogates are often unable to match the vaporization behavior and physical properties of the real fuel and fail to capture the effect of preferential vaporization on combustion behavior. Therefore, a computationally efficient, hybrid droplet vaporization-chemical surrogate approach has been developed which emulates both the physical and chemical properties of a multicomponent kerosene fuel. The droplet vaporization/physical portion of the hybrid uses the Coupled Algebraic–Direct Quadrature Method of Moments with delumping to accurately solve for the evolution of every discrete species in a vaporizing fuel droplet with the computational efficiency of a continuous thermodynamic model. The chemical surrogate portion of the hybrid is linked to the vaporization model using a functional group matching method, which creates an instantaneous surrogate composition to match the distribution of chemical functional groups (CH₂, (CH₂)_n, CH₃ and Benzyl-type) in the vaporization flux of the full fuel. The result is a hybrid method which can accurately and efficiently predict time-dependent, distillation-resolved combustion property targets of the vaporizing fuel and can be used to investigate the effects of preferential vaporization on combustion behavior.     

Detailed and simplified kinetic models of n-dodecane oxidation: The role of fuel cracking in aliphatic hydrocarbon combustion

A detailed kinetic model is proposed for the combustion of normal alkanes up to n-dodecane above 850 K. The model was validated against experimental data, including fuel pyrolysis in plug flow and jet-stirred reactors, laminar flame speeds, and ignition delay times behind reflected shock waves, with n-dodecane being the emphasis. Analysis of the computational results reveal that for a wide range of combustion conditions, the kinetics of fuel cracking to form smaller molecular fragments is fast and may be decoupled from the oxidation kinetics of the fragments. Subsequently, a simplified model containing a minimal set of 4 species and 20 reaction steps was developed to predict the fuel pyrolysis rate and product distribution. Combined with the base C₁-C₄ model, the simplified model predicts fuel pyrolysis rate and product distribution, laminar flame speeds, and ignition delays as close as the detailed reaction model.     

A multi-zone chemistry mapping approach for direct numerical simulation of auto-ignition and flame propagation in a constant volume enclosure

A direct numerical simulation (DNS) coupling with multi-zone chemistry mapping (MZCM) is presented to simulate flame propagation and auto-ignition in premixed fuel/air mixtures. In the MZCM approach, the physical domain is mapped into a low-dimensional phase domain with a few thermodynamic variables as the independent variables. The approach is based on the fractional step method, in which the flow and transport are solved in the flow time steps whereas the integration of the chemical reaction rates and heat release rate is performed in much finer time steps to accommodate the small time scales in the chemical reactions. It is shown that for premixed mixtures, two independent variables can be sufficient to construct the phase space to achieve a satisfactory mapping. The two variables can be the temperature of the mixture and the specific element mass ratio of H atom for fuels containing hydrogen atoms. An aliasing error in the MZCM is investigated. It is shown that if the element mass ratio is based on the element involved in the most diffusive molecules, the aliasing error of the model can approach zero when the grid in the phase space is refined. The results of DNS coupled with MZCM (DNS-MZCM) are compared with full DNS that integrates the chemical reaction rates and heat release rate directly in physical space. Application of the MZCM to different mixtures of fuel and air is presented to demonstrate the performance of the method for combustion processes with different complexity in the chemical kinetics, transport and flame–turbulence interaction. Good agreement between the results from DNS and DNS-MZCM is obtained for different fuel/air mixtures, including H₂/air, CO/H₂/air and methane/air, while the computational time is reduced by nearly 70%. It is shown that the MZCM model can properly address important phenomena such as differential diffusion, local extinction and re-ignition in premixed combustion.