煤粉的增压富氧燃烧特性及煤灰矿物演变

为了更好地了解煤粉在增压富氧条件下的燃烧过程,利用加压热天平(PTGA)结合X射线衍射仪(XRD),研究了增压富氧燃烧条件下压力对煤粉燃烧特性及煤中矿物演变的影响。研究表明,随着压力的升高,煤粉常压时的非均相着火逐渐转变为均相着火,当压力升高到3 MPa开始向非均相着火过渡,并在5 MPa时完全转变成非均相着火。由于煤粉着火机理的转变,综合燃烧特性指数S随着压力的增加先升高后降低。不同的着火机理下,煤粉的燃烧温度也会有所差别。常压时非均相着火较高的燃烧温度使得反应生成了莫来石等矿物,而1 MPa时均相着火较低的燃烧温度则使得煤灰中出现了伊利石等矿物。压力继续升高,均相着火开始向非均相着火过渡,燃烧温度逐步升高,伊利石逐渐转变为莫来石。     

Effect of radiation absorption modes on ignition time of translucent polymers subjected to time-dependent heat flux

Majority of previous solid ignition models, including numerical and analytical ones, considered only surface absorption of incident heat flux for simplification. However, the influence of in-depth absorption on pyrolysis and subsequent ignition cannot be ignored for infrared translucent polymers. This work addresses this problem and focuses on time-dependent heat flux to establish an analytical model for ignition behaviors prediction by means of theoretical analysis. Ignition temperature was utilized as the ignition criterion, and both surface and in-depth absorption scenarios were considered. Thermally thick polymethyl methacrylate and polyamide 6 were selected as reference materials to verify the reliability and applicability of the proposed model by comparing the analysis results with experimental data as well as numerical simulations. A method for determining the approximation parameters of the theoretical analysis was presented to derive the relationship between ignition time and the coefficients in heat flux expressions. The results show that the higher surface temperature owing to surface absorption accelerates the pyrolysis rate and results in a shorter ignition time, while in-depth absorption affects the ignition time inversely. The effect of surface heat loss was also evaluated quantitatively through both analytical and numerical models. The uncertainty of the proposed model is mainly caused by the selection of the approximation parameters. Nevertheless, it provides an alternative approach to estimate the ignition time of translucent polymers besides numerical simulation.

     

Mathematical Modeling of Aluminum Diboride Combustion in an Air Flow

A mathematical model and the results of calculating the ignition and combustion of energetic condensed systems based on mono- and polydispersed aluminum diboride particles in air flows in constant-cross-section channels are reported. The kinetic characteristics of the transformations that separate aluminum diboride particles formed by gasification of energetic condensed systems undergo in a high-temperature oxidizing medium were determined using the dependences of the ignition induction period and combustion time on the air temperature and diameter and initial temperature of the particles. These dependences, in turn, were calculated using the model of parallel chemical reactions. The range of combustion conditions corresponding to the initial air temperatures from 300 to 2000 K and Mach numbers in the channel from 0.1 to 1.5 was considered. The influence of the aluminum diboride particle size and of the rate and initial temperature of the air flow on the combustion efficiency was demonstrated. The relationships between the combustion completeness factor of aluminum diboride particles at various initial parameters of the air flow and gasification products of energetic condensed systems at various fuel mixture equivalence ratios, corresponding to the diffusion and kinetic combustion, were determined. The conditions of the transition between the diffusion and kinetic control modes were found.

     

C1-C4在Pt 催化剂上的多相反应机理

提出并构建了H2和C1-C4碳氢燃料在Pt表面上的详细催化反应机理, 对所构建的机理分别用CH4、C2H6、C3H8以及C4H10等碳氢燃料进行了数值模拟; 并用文献中给定的部分碳氢燃料(如CH4、C2H6 加H2与不加H2, C3H8加H2与不加H2, 以及C4H10加H2)的催化着火与燃烧的实验结果与数值模拟结果进行了对比, 对比结果表明H2会对C3H8以及C4H10的催化起燃以及C2H6的催化燃烧起促进作用, 但所起作用的动力学过程并不是相同的. 此机理能够有效地反映上述燃料的主要催化着火以及催化燃烧特征, 并可以对着火与燃烧整个过程进行动力学分析, 用其来描述C1-C4碳氢燃料的催化着火与燃烧具有一定的合理性.     

Ignition and combustion characteristics of compound of magnesium and boron

Compound of magnesium and boron (MB) is promising to be the ideal substitute of amorphous boron which is usually used as the raw material of boron-based fuel-rich propellants. In this study, the physical characteristics of MB and amorphous boron were studied by the scanning electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. The thermal reaction characteristics and the ignition and combustion characteristics were investigated through TG/DSC experiments and laser ignition experiments. The experimental results show that the MB particle is much more regular than amorphous boron, which favors for the preparation of boron-based fuel-rich propellants. Magnesium exists in the form of elementary substance, and boron oxide is produced during the preparation of MB which results in the longer ignition delay time of MB. The content of magnesium and the pressure have effects on the MB combustion performance. Although the combustion of magnesium can provide much heat for the combustion of boron, MB with moderate content of magnesium shows the best combustion performance. On the contrast, the ignition delay time of MB is independent on the content of magnesium and the pressure.     

A TG/DTA study on the effect of coal blending on ignition behaviour

Understanding the ignition behaviour of coal is of utmost importance for the design of boilers and control of the combustion process. In recent years there has been an increasing utilisation of coal blends for combustion, but information on the possible interactive effects during ignition of the individual components is scarce. In this work the ignition behaviour of a series of coal blends, made up from three coals of different rank, sub-bituminous, high volatile and low volatile bituminous, was studied. To this end a thermogravimetric analyser linked to a mass spectrometer for evolved gas analysis was used. Different ignition behaviour was observed for the coals studied; the sub-bituminous and low volatile bituminous coals ignited heterogeneously, while homogeneous ignition occurred for the high volatile bituminous coal. In the case of blends of the low and high volatile bituminous coals, different mechanisms of ignition were observed depending on the blends composition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Practical aspects of modeling ignition and burning of organic polymers 1. The case of PE loaded with mixtures of Al (OH)3 and Hg(OH)2 or MgCO3

A correlation has been found between limiting oxygen index and tendency towards decomposition into volatiles as determined from nonisothermal thermogravimetry for polyethylene charged with the mixtures of Al(OH)₃ and Mg(OH)₂ or MgCO₃. An interpretation based on the model of ignition and burning of polymers has been put forward and a dependence of heat transfer coefficient on temperature of ignition and initial mass of sample was found.     

双燃料发动机缸内分层激光诱导荧光实验及化学动力学模拟研究

双燃料压燃（RCCI）是一种很有前景的发动机新型燃烧方式,能在小负荷到中高负荷范围内实现发动机高效清洁燃烧,为了将RCCI拓展到更高负荷,需要对其缸内燃油分层和燃烧过程开展更深入研究。本文在一台双燃料光学发动机上采用燃油-示踪剂平面激光诱导荧光法（PLIF）,对RCCI着火前缸内燃油分层进行定量测量,选用甲苯作为示踪剂,利用266 nm脉冲激光激发甲苯荧光,发动机转速1200 r·min^-1,平均指示压力6.9×10⁵ Pa,气道喷射异辛烷,缸内在上止点前10°喷射正庚烷。采用燃油-气体绝热混合假设,对PLIF测量结果进行温度不均匀性修正,以上止点后5°曲轴转角下的测量结果为例,不修正相比修正测试区域内的最大当量比高估15%。根据实验结果,利用Chemkin软件分析了活性、浓度和温度分层对燃烧滞燃期的影响,结果显示燃料活性分层和浓度分层共同决定RCCI的着火滞燃期,其中活性分层影响要大于浓度分层,而温度分层对着火滞燃期影响很小。RCCI燃烧过程自发光的高速成像结果表明,着火过程首先出现在燃烧室边缘的高活性区域,随后火焰向燃烧室中心处的低活性区域发展,碳烟辐射光图像显示碳烟主要形成于燃烧室边缘的高活性区域。     

甲基肼/四氧化二氮反应化学动力学模型构建及分析

甲基肼(MMH)和四氧化二氮(NTO)是常用的液体火箭发动机推进剂,但目前对其反应机理的研究还十分有限.本文首先构建了一个包含23种组分和20个基元反应的MMH/NTO反应动力学模型;对MMH/NTO自燃着火过程进行的验证计算表明,该机理能够合理地描述MMH/NTO的自燃温升过程,准确预测反应物系统的着火延迟时间及平衡温度,并能合理地反映MMH/NTO反应物系统着火延迟时间对反应初始压力以及氧燃比的依赖关系;通过灵敏度分析方法指出了影响MMH/NTO着火过程的关键反应.模拟分析了在不同压力和氧燃比条件下MMH/NTO系统的自燃温升过程,结果表明,随着压力的升高,系统着火延迟时间变短,平衡温度升高;在一定范围内增大氧燃比,着火延迟时间变长,平衡温度先升高后减小.     

RP-3替代燃料自点火燃烧机理构建及动力学模拟

通过对RP-3 航空煤油成分的分析, 以及对8 组替代模型的对比实验, 选取了73.0%(质量分数)正十二烷, 14.7% 1,3,5-三甲基环己烷, 12.3%正丙基苯作为RP-3 航空煤油的替代模型. 使用本课题组自主研发的机理自动生成程序ReaxGen, 构建了RP-3 替代燃料的高温燃烧详细机理, 用该机理模拟了激波管点火延时, 并与实验数据进行比较. 用物质产率分析和近似轨迹优化算法(ATOA)简化方法简化了详细机理. 最后对燃烧机理在不同化学计量比及压力条件下的点火延时做了敏感度分析, 考察了燃烧机理在不同化学计量比下关键反应的异同. 结果表明, 该替代模型的燃烧机理能很好地描述RP-3煤油的高温点火特性.     

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。     

汽油多组分表征燃料简化动力学模型的系统化构建及验证

提出了一套系统化多级机理简化策略,包含基于误差传播的直接关系图法、峰值浓度分析法、线性同分异构体集总法、主组分分析法、温度敏感性分析和产率分析法,并将其应用于汽油四组分表征燃料详细反应机理的简化,构建了适用于HCCI发动机燃烧边界下的简化机理模型,包含149个物种、414个反应。通过与激波管、快速压缩机、增压HCCI发动机实验数据的对比验证表明,新机理可以准确地预测较宽范围条件下的着火滞燃期,在HCCI发动机的单区模型计算中,该机理对缸内燃烧和排放的预测结果是令人满意的。放热率分析表明, R + O₂反应是控制中间温度区放热的关键基元反应,在高压低温下,异辛烷的放热起到决定性作用。添加2-戊烯之后,使得四组分模型相较于三组分模型更为准确,尤其是对于第一阶段着火滞燃期有显著影响,为进一步探索调和燃料组分比例控制HCCI燃烧提供了一条新思路。     

Changes in the composition of synthesis products upon transitioning from self-ignition to combustion

Changes in the chemical composition of condensed products upon switching from synthesis in the self-ignition mode to combustion synthesis is studied by approximate analytical and numerical means for condensed substances that react via competing reaction pathways. It is shown that these different modes of synthesis produce different compositions of the reaction products. The conditions required for transitioning from one mode of combustion initiation (thermal explosion) to another (ignition) are determined. It is found that this transition can occur upon changing the temperature of a heater by just two characteristic intervals. A scaling procedure that allows the calculation results obtained at zero dimensionless temperature of the heater to be used to determine the effect its non-zero dimensionless temperature has on the ignition mode and the composition of the obtained products is proposed. Calculations show that materials with different distributions of the chemical composition along the sample can be obtained by deliberately changing the temperature of the heater.     

差热分析测定水煤浆的燃烧特性

水煤浆具有燃烧效率高、燃烧温度低、环境污染少等特点,是当前国内、外广泛研究的课题之一,具有广阔的发展前途。通常水煤浆含有30—35%的水,0.1—1%的添加剂,这大量水和少量添加剂的存在对水煤浆的燃烧过程所产生的影响以及它与煤粉的直接燃烧的差别是我们共同关心和感兴趣的问题。本文利用差热分析仪直接测定两种煤粉及由三种不同添加剂制得的水煤浆在空气流中燃烧时的特性。     

胜利褐煤燃烧中未反应残留物结构特性及铁的添加效应

利用TGA确定胜利褐煤盐酸脱灰煤和添加铁组分脱灰煤的着火温度,在着火温度进行燃烧反应,收集燃烧反应一定时间后的未反应残留物,利用FT-IR、XPS、XRD和Raman等对其进行表征,研究了胜利褐煤燃烧过程中铁的影响规律。结果表明,铁的加入降低脱灰胜利褐煤的着火温度,当添加量为3.50%时,着火温度降低的幅度最大。在着火温度燃烧反应一定时间后未反应残留物的FT-IR表明,其有机官能团结构无显著变化,说明铁的添加并不影响其有机官能团结构特性,有机官能团不会对燃烧性能产生太大的影响。添加铁使SL+在燃烧过程中未反应残留物结构芳香度下降,晶面间距增大,晶体结构中缺陷位相对增加,石墨化程度降低,烷基侧链增多,碳氧结构迅速减少,说明铁组分的加入改变了其燃烧过程中碳氧结构转化特性,抑制了石墨化转化速率与程度,即在燃烧反应过程中改变了其未反应残留物的微结构,从而改变了其反应历程,加速燃烧反应速率。     

Kinetic model of liquid B2O3 gasification in a hydrocarbon combustion environment: I. Heterogeneous surface reactions

As part of an ongoing program to model hydrocarbon assisted boron combustion, a kinetic model has been developed to describe gasification of the ubiquitous boron oxide coating that inhibits particulate boron ignition. This model includes homogeneous gas phase oxidation reactions, multi-component gas phase diffusion, heterogeneous surface reactions, and oxide vaporization. The kinetic processes are treated using a generalized kinetics code, with embeded sensitivity analysis, for the combustion of a one-dimensional (particle radius), spherical particle. This article presents the heterogeneous surface reactions used to describe oxide gasification and presents selected model results for a spherical boron oxide droplet which illustrate the dependence of the oxide gasification rates on the ambient temperature and particle diameter.     

Interactions Between Surface Reactions and Gas-phase Reactions in Catalytic Combustion and Their Influence on Ignition of HCCI Engine

IntroductionThe phenomenon of catalytic combustion was firstdiscovered in 1817 when Humphry Davy observed thatPt wires could promote combustion reactions in flamma-ble mixtures. Since then, considerable efforts havebeen focused on the application of catal…     

Analysis of the dynamics of coal char combustion with ignition and extinction phenomena: Shrinking core model

Single‐particle combustion of coal char is analyzed using a generalized shrinking core model. Finite volume method, which was earlier employed by the authors in solving moving boundary problems involving fluid–solid noncatalytic reactions in general, is used to solve fully transient mass and energy equations. The model takes into account convection and diffusion inside the particle as well as in the boundary layer. The computed results are compared with the experimental data of the authors for combustion of coal char in a fluidized bed combustor. The effects of parameters such as bulk temperature and initial particle radius on the combustion dynamics are examined. The phenomena of ignition and extinction are also investigated. Finally, the importance of Stefan flow, originating due to nonequimolar counterdiffusion, on combustion of coal char is analyzed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 569–582, 2008     

采用系统的方法自动构建链烷烃高温燃烧反应机理

为了得到合理可靠和简化的反应机理,利用反应机理自动生成程序ReaxGen,构建了正庚烷、异辛烷、正癸烷和正十二烷的高温燃烧反应详细机理;同时分别采用物质产率分析和反应路径流量分析的方法对详细机理进行简化,得到了半详细机理和骨架机理. 在较宽的温度和压力条件下,对半详细机理和骨架机理进行了点火延时、层流火焰传播速度和重要物种浓度曲线的模拟并与实验结果比较;最后,图示说明了这些烷烃的主要高温燃烧路径,给出了点火延迟时间的敏感度分析. 结果表明：这些机理能够合理描述链烷烃的自点火特性,文中提出的结合ReaxGen程序的机理构建方法和反应路径流量分析的简化方法也可以用于其它烃类的高温燃烧机理构建.     

Thermal analysis study of the effect of coal-burning additives on the combustion of coals

Thermal analysis is widely used in combustion research for both fundamental and practical investigations. Efficient combustion of coals in cement industry is very important and necessary. In this research, the effects of three coal-burning additives on burning behaviour of bituminous coal and anthracite were studied with the help of thermogravimetry (TG) and differential scanning calorimetric (DSC) analysis. The kinetic study was carried out and the results were presented. The results showed that the coal-burning additives especially LSZ can reduce the ignition temperature, increase the ignition index D _i, combustion ending index D _f and affect the activation energy of the coal samples studied. The coal-burning additives especially LSZ can improve coal combustion effectiveness.