Challenges and perspectives of combustion chemistry research

In the past decades, combustion chemistry research grew rapidly due to the development of combustion diagnostic methods,quantum chemistry methods, kinetic theory, and computational techniques. A lot of kinetic models have been developed for fuels from hydrogen to transportation fuel surrogates. Besides, multi-scale research method has been widely adopted to develop comprehensive models, which are expected to cover combustion conditions in real combustion devices. However, critical gaps still remain between the laboratory research and real engine application due to the insufficient research work on high pressure and low temperature combustion chemistry. Besides, there is also a great need of predictive pollutant formation model. Further development of combustion chemistry research depends on a closer interaction of combustion diagnostics, theoretical calculation and kinetic model development. This paper summarizes the recent progress in combustion chemistry research briefly and outlines the challenges and perspectives.     

脉冲电晕放电下的甲烷氧化偶联反应(英文)

研究了在常温,常压及惰性气体稀释的条件下,用脉冲电晕放电进行的甲烷氧化偶联（OCM）反应。在各种实验条件下,产物CZ烃由一6o／o乙烯,－70rk乙烷和一87％乙炔组成。甲烷的转化率及CZ烃的生成速率依赖于反应气中甲烷与氧气的比值,它们的流速及直流电源的电压等n通过调节这些实验条件,甲烷转化为C4烃的转化率可得到优化,在45kV高压,30ml。／min的流速下（反应气体组成为95％CHn与50／0O2）,CZ烃的最高选择性可达85O／O。当反应气体组成为80％CH4和20O／oOZ时,甲烷的最高转化率达23％。在间歇式反应器中,甲烷转化率随反应时间增长而提高,反应75分钟时甲烷转化率达7lO／O,而CZ烃的产物分布,尤其是乙炔的含量随反应时间增长而明显降低,这些实验结果支持了文献中提出的ZCH4～CZH6—CZH4～CZHZ～CO／COZ反应历程。     

A simple reactive gasdynamic model for the computation of gas temperature and species concentrations behind reflected shock waves

A simple gasdynamic model, called CHEMSHOCK, has been developed to predict the temporal evolution of combustion gas temperature and species concentrations behind reflected shock waves with significant energy release. CHEMSHOCK provides a convenient simulation method to study various sized combustion mechanisms over a wide range of conditions. The model consists of two successive suboperations that are performed on a control mass during each infinitesimal time step: (1) first the gas mixture is allowed to combust at constant internal energy and volume; (2) then the gas is isentropically expanded (or compressed) at frozen composition to the measured pressure. The CHEMSHOCK model is first validated against results from a one‐dimensional reacting computational fluid dynamics (CFD) code for a representative case of heptane/O₂/Ar mixture using a reduced mechanism. CHEMSHOCK is found to accurately reproduce the results of the CFD calculation with significantly reduced computational time. The CHEMSHOCK simulation results are then compared to experimental results, for gas temperature and water vapor concentration, obtained using a novel laser sensor based on fixed‐wavelength absorption of two H₂O rovibrational transitions near 1.4 μm. Excellent agreement is found between CHEMSHOCK simulations and measurements in a progression of shock wave tests: (1) in H₂O/Ar, with no energy release; (2) in H₂/O₂/Ar, with relatively small energy release; and (3) in heptane/O₂/Ar, with large energy release. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 189–198, 2008     

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。     

Theoretical investigation of the gas-phase kinetics active during the GaN MOVPE

Quantum chemistry investigations have been performed to study the gas-phase chemistry active during the MOVPE of GaN when Ga(CH3)(3) and NH3, diluted in a H2 carrier gas, are used as precursors. Optimized molecular geometries, energies, and transition-state structures of gas-phase species have been determined with density functional theory at the B3LYP/6-311+g(d,p) level. On the basis of the similarity with the soot formation mechanism active during hydrocarbon combustion, we propose that in this system a gas-phase chemistry is active and its reactivity is enhanced by a radical chain mechanism started from methyl radicals. Initiation reactions are surface processes or the pyrolysis of Ga(CH3)(3). A propagation mechanism composed of fast radical reactions, most of which without an activation energy, was identified, and kinetic constants were determined for each step. The proposed mechanism is able to describe the formation of large GaN adducts formed by up to three R-Ga-NH units. These molecules can give fast cyclization reactions that lead to the formation of six-membered cyclic species, which, similar to benzene for combustion, are thermodynamically stable in vast temperature and pressure ranges and can thus be considered as the first GaN nuclei. We also found that the presence of H2 as a carrier gas can greatly enhance the rate of formation of gas-phase particles because it is a major source of atomic hydrogen, a promoter of gas-phase reactivity.     

CaO对褐煤在超临界水中制取富氢气体的影响

以褐煤在超临界水中制取富氢气体为目的,利用小型高压间歇反应装置,在Ca/C 摩尔比为0～0.60、温度450℃～680℃、压力23MPa～38MPa和停留1min～30min下,考察了小龙潭褐煤的反应特性。研究表明,CaO不仅可以固定气相中的CO2,提高H2的体积分数,而且可以提高碳转化率和气体产率。600℃、28MPa,Ca/C摩尔比为0.42时,气相产物中的CO2趋于完全固定,H2产率比无添加剂时提高2.5倍,H2体积分数为48％,其余为CH4和烃类气体。升高反应温度使CaO的催化作用更为显著, 碳转化率和气体产率（H2、CH4、烃类气体）随着反应温度的升高而逐渐增加,液相收率减少。增大反应压力可以促使煤转化率和气体产率升高,停留时间对反应的影响相对较小。以900℃热解焦为反应原料进行了气化实验,结果表明,在600℃和650℃反应5min后,碳转化率分别为8.6％和12.5％,CaO对气化反应和甲烷化反应起不同程度的催化作用。     

Detailed kinetic modeling of 1,3‐butadiene oxidation at high temperatures

The high‐temperature kinetics of 1,3‐butadiene oxidation was examined with detailed kinetic modeling. To facilitate model validation, flow reactor experiments were carried out for 1,3‐butadiene pyrolysis and oxidation over the temperature range 1035–1185 K and at atmospheric pressure, extending similar experiments found in the literature to a wider range of equivalence ratio and temperature. The kinetic model was compiled on the basis of an extensive review of literature data and thermochemical considerations. The model was critically validated against a range of experimental data. It is shown that the kinetic model compiled in this study is capable of closely predicting a wide range of high‐temperature oxidation and combustion responses. Based on this model, three separate pathways were identified for 1,3‐butadiene oxidation, with the chemically activated reaction of H^· and 1,3‐butadiene to produce ethylene and the vinyl radical being the most important channel over all experimental conditions. The remaining uncertainty in the butadiene chemistry is also discussed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 589–614, 2000     

用无声放电转化甲烷和二氧化碳同时制备合成气与烃

在低温常压条件下,研究了在无声放电反应器中以A型分子筛为催化剂从甲烷和二氧化碳合成烃和合成气,实现了在无声放电反应器中同时合成烃和合成气。实验在原料气流量200－600ml/min、原料气甲烷和二氧化碳摩尔比1／1－3／1及输入功率100－500W的范围内进行。研究结果表明,低原料气流量有利于甲烷和二氧化碳的转化,而高原料气流量有利于烃的生成;原料气甲烷和二氧化碳摩尔比对制得合成气的H2／CO摩尔比的影响最显著;甲烷和二氧化碳转化率及合成气和烃的产率均随输入功率的增加而提高。而所研究的范围内,当原料气流理为200ml/min、甲烷和二氧化碳摩尔比为1／1、输入功率为500S时,甲烷和二氧化碳转化率达到最高值,分别为64％和39％。以此法制备的合成气的H2／CO摩尔可以在很宽的范围内变化,本研究合成气H2／CO摩尔比的变化范围是0.7-3.1。     

Modeling of microreactor for syngas production by catalytic partial oxidation of methane

Fixed-bed reactors for the catalytic partial oxidation of methane (CPOM) to produce synthesis gas still pose hot spots problems. Microreactor is a good alternative reactor proposed to resolve these problems. In this paper, synthesis gas (hydrogen and carbon monoxide) production was investigated by a two-dimensional numerical model of single microchannel. CFD modeling with detailed chemistry was conducted to understand the CPOM on platinum (Pt) catalyst. Gas inlet velocity, microchannel pressure, and fuel to air ratio (F/A) are selected as the effective parameters on microchannel performance. Study results show that Reynolds number has considerable effect on methane conversion, hydrogen to carbon monoxide ratio (H2/CO), and product distribution. Increasing gas inlet velocity causes all the above parameters to decrease. It is noted that increasing microchannel pressure and decreasing the ratio of fuel to air cause the decrease of the H2/CO ratio.     

Experimental and modeling studies of B atom number density distributions in hot filament activated B2H6/H2 and B2H6/CH4/H2 gas mixtures

Experimental and modeling studies of the gas-phase chemistry occurring in dilute, hot filament (HF) activated B2H6/H2 and B2H6/CH4/H2 gas mixtures are reported. Spatially resolved relative number densities of B (and H) atoms have been measured by resonance enhanced multiphoton ionization methods, as a function of process conditions (e.g. the HF material and its temperature, the B2H6/H2 mixing ratio, and the presence (or not) of added CH4). Three-dimensional modeling of the H/B chemistry prevailing in such HF activated gas mixtures using a simplified representation of the gas phase chemistry succeeds in reproducing all of the experimentally observed trends, and in illustrating the key role of the "H-shifting" reactions BHx + H <= => BHx-1 + H2 (x = 1-3) in enabling rapid interconversion between the various BHx (x = 0-3) species. CH4 addition, at partial pressures appropriate for growth of boron-doped diamond by chemical vapor deposition methods, leads to approximately 30% reduction in the measured B atom signal near the HF. The modeling suggests that this is mainly due to concomitant H atom depletion near the HF, but it also allows us a first assessment of the possible contributions from B/C coupling reactions upon CH4 addition to HF activated B2H6/H2 gas mixtures.     

Oxidative Coupling of Methane over Na-W-Mn/SiO2 Catalysts at Elevated Pressures

Na-Mn-W/SiO2 catalysts were studied for the oxidative coupling of methane (OCM) in a micro fixed bed reactor made of stainless steel reactor at elevated pressures. The effect of operating conditions, such as GHSV, pressure, temperature and CH4/O2 ratio on the catalytic performance of OCM was investigated. The C2+ selectivity of 80.3% was obtained at a CH4 conversion of 16.1% at 750℃,1.5× 105h-1 GHSV, and 0.6 MPa. Also, there is a small output of C3 and C4 hydrocarbons in the tail gas. The results show that unfavorable effects due to elevated pressure can be overcome by increasing GHSV, and the OCM reaction is strongly dependent on the operating conditions at elevated pressures,particularly GHSV and the CH4/O2 ratio.     

两相流中煤粉的燃烧机理及动力学特征

利用微型流化床动力学分析仪研究了两相流条件下无烟煤粉的燃烧反应机理和动力学特征,并与热重法所得结果进行比较分析。结果表明,当温度大于850℃时,煤粉燃烧机理发生了变化,燃烧气态产物的生成比例也随之改变;当气速大于0.10 m/s时,气体扩散限制基本被消除,煤粉燃烧反应速率主要受界面化学反应控制;煤粉燃烧反应速率随着氧气分压的增大呈幂函数形式增长,且氧气分压对煤粉静置燃烧的影响更加显著。煤氧两相流燃烧的表观活化能与静置燃烧相比降低了49 kJ/mol,相同温度条件下两相流燃烧的界面化学反应阻力也明显小于热重法测试结果。     

High pressure effects on the mutual sensitization of the oxidation of NO and CH4-C2H6 blends

The mutual sensitization of the oxidation of NO and a CH(4)-C(2)H(6) (10 : 1) simulated natural gas (NG) blend was studied under fuel lean conditions (Phi = 0.5) at 50 atm and 1000-1500 K in the UIC high pressure shock tube (HPST). New experimental results were also obtained for the mutual sensitization of methane and the NG blend in the CNRS jet stirred reactor (JSR) at 10 atm. A detailed chemical kinetic model was assembled to describe the observed changes in reactivity in the CH(4) and NG blends, with and without NO, in the HPST and the JSR. The data and the validated model (tested against a variety of targets) show a reduced difference of reactivity between methane and NG blends in the presence of NO at characteristic reaction times for the JSR (250-1000 micros). However the HPST data and subsequent simulations using the validated model have revealed that at higher pressures and in the millisecond time scale regime representative of the HPST experiments (and practical combustion devices) there still persists a significant difference in reactivity between methane and NG blends in the presence of NO. The experimental data, the model development and validations and its predictions and utility as a tool to probe the NO-hydrocarbon sensitization effects under practical combustion conditions is discussed.     

A new method for determining delta13C and deltaD simultaneously for CH4 by gas chromatography/continuous-flow isotope-ratio mass spectrometry

A continuous-flow technique has been developed to analyse the deltaD and delta(13)C values for CH(4) from gas samples, in a single run. This is achieved by splitting the sample gas stream and directing the streams simultaneously through a CuNiPt combustion reactor and an alumina pyrolysis reactor. The CO(2) from CH(4) combustion is trapped in a liquid nitrogen trap while the H(2) exiting the pyrolysis reactor is directed to the mass spectrometer for deltaD(CH4) determination. The CO(2) is then sublimed and directed to the mass spectrometer for delta(13)C(CH4) determination. Sample runs take approximately 10 minutes. This technique gives accurate delta(13)C(CH4) results to within +/-0.3-0.5 per thousand and deltaD(CH4) results to within +/-2-5 per thousand. Injection volumes between 0.5 and 2.5 microL of CH(4), equivalent to between 20 and 100 nmol CH(4), are required for accurate delta(13)C and deltaD analyses, respectively, using sample injection into a split flow with a split ratio of 10. This method provides rapid, accurate and reproducible results on multiple sample runs and is, therefore, an ideal method for analysing natural gas samples from a variety of sources.     

Modelling the effect of operating conditions on hydrodynamics and mass transfer in a Pd–Ag membrane module for H2 purification

In this work a novel modelling approach based on Computational Fluid Dynamics (CFD) for the prediction of the gas separation process in a Pd–Ag membrane module for H₂ purification is presented. With this approach, the pressure and velocity flow fields of the gas mixture and the species concentration distribution in the selected three-dimensional domain are simultaneously and numerically computed by solving the continuity, momentum and species transport equations, including a gas-through-gas diffusion term derived from the Stefan–Maxwell formulation. As a result, the H₂ permeation calculations depend on the local determination of the mass transfer resistances offered by the gas phase and by the membrane, which is modelled as a permeable surface of known characteristics. The applicability of the model to properly predict the separation process under a wide range of pressure, feed flow rate, temperature and gas mixtures composition is assessed through a strict comparison with experimental data. The influence of inhibitor species on the module performance, that is obtained by implementing in the CFD model a suitable literature correlation, is also discussed.     

固体热载体热解淮南煤实验研究

自制处理量为1 kg煤的间歇式固体热载体热解装置,以淮南烟煤为原料,石英砂作热载体,对该煤进行热解特性评价实验。考察了热载体初始温度700 ℃～900 ℃、反应 4 min～16 min、煤粒径及热载体与煤的质量比5～9对热解产物产率和性质的影响。结果表明,提高热载体初始温度,气、液产率增加;延长反应时间和提高热载体比例,气体产率有所增加;热载体初始温度对热解气组成影响显著。提高热载体与煤的质量比和热载体初始温度,可以抑制半焦对热解反应器内壁的黏附。     

甲烷氧等离子体直接合成过氧化氢

本文利用介质阻挡放电(DBD)方法, 在室温和常压下将甲烷和氧气的混合气体进行等离子体活化, 通过甲烷和氧等离子体直接气相反应高收率合成H2O2. 该方法能有效克服氢氧直接法合成H2O2受到原料气配比严格限制的缺点.     

CFD Model of Dense Gas-solid Systems in Jetting Fluidized Beds

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旋流煤粉燃烧的一维综合数值模拟

发展了综合考虑气－固两相旋流流动，气相燃烧，颗粒相变与燃烧及两相辐射传热的旋流煤粉燃烧－维数学模型，给出了气－固两相能量方程中颗粒相就源项的计算表达式，应用这一模型对涡旋燃烧炉环形通道内多组工况的旋流气体燃烧和煤粉燃烧进行了数值模拟，计算得到的炉内温度分布和燃烧效率与实验数据基本相符，表明本文建立的模型可用于旋流煤粉燃烧的一维综合数值模拟。     

Simulation of a mixed-conducting membrane-based gas turbine power plant for CO<Subscript>2</Subscript> capture: system level analysis of operation stability and individual process unit degradation

A gas turbine power plant for CO₂ capture, based on oxygen-permeable membranes with mixed ionic-electronic conductivity, was analysed with respect to long-term stability by means of numerical simulation. Due to the attractive transport and physicochemical properties of mixed-conducting La₂NiO_4+δ, this nickelate was selected as a prototype membrane material for this application. Experiments showed very slow degradation of La₂NiO_4+δ membranes at oxygen chemical potentials close to atmospheric conditions, which are associated with kinetic demixing and other microstructure-related factors. Interaction with CO₂ in the intermediate temperature range also leads to lower oxygen permeation, whilst increasing oxygen pressure may cause partial phase decomposition and microstructural changes, thus again limiting the range of possible operation conditions. The relevant operational constraints were included in a detailed membrane-based gas turbine power plant model. The membrane performance degradation with time was approximated by a linear function with average rate of 3.3% per 1,000 operation hours. Furthermore, performance deterioration of the gas turbine compressor and turbine were also considered. Simulations revealed that the power plant is substantially affected by degradation of the ceramic membranes and turbomachinery components. The already rather small operating window was further narrowed when compared with a conventional gas turbine power plant. Two different designs of the membrane-based power plant were analysed: (1) with and (2) without additional combustors (afterburners) between the membrane reactor and the gas turbine. Afterburners increase thermal efficiency as well as power output, but also lead to non-negligible CO₂ emissions. In order to have a frame of comparison, results for a conventional gas turbine power plant with degradation of turbomachinery components are also presented. Simulations representing changes in ambient temperature and fuel composition as well as failure incidents were executed to analyse the susceptibility of the gas turbine power plant to external and internal changes.