基于燃烧化学反应原理的民机防火工程技术课程建设

民机载有大量的航空燃料,一旦发生泄露燃烧,生成大量的热量,容易引燃飞机机体材料,因此民机防火技术是确保民航运输业安全运行的重要保障。《民机防火工程技术》是我校安全科学与工程学术型硕士研究生的专业课程,本课程主要讲授燃烧化学反应基本原理、飞机防火技术的基本概念和技术现状,以及飞机各舱室防火技术的研究进展。在课程建设过程中,将民航专业知识由浅入深地融入到课程内容中。本文阐述了课程建设内容、案例教学法的设计与实施。教学效果表明,案例教学法能显著提高学生的学习兴趣和积极性,能够根据实际问题提出解决方案,培养了学生的创新思维和团结协作精神。

氨氢融合零碳内燃机燃烧过程综述

随着中国“碳达峰”与“碳中和”目标的提出,内燃机低碳化、零碳化势在必行。氨作为零碳燃料和氢的高能量密度载体,是实现碳中和有潜力的替代燃料。研发氨氢燃烧技术,实现氨高效清洁融合燃料零碳大功率内燃机高效近零排放对全球气候治理具有重大意义。该文在分析氨作为未来绿色能源的潜力及其在内燃机中实际应用的基础上,从氨氢内燃机的燃烧模式、氨氢燃料的燃烧化学反应动力学、氨氢燃料供给方式等方面综述了氨氢内燃机的燃烧的最新进展,对比分析了火花点燃/均质压燃/射流引燃3种燃烧模式、氨气道喷射/液氨缸内直喷2种燃料供给方式、主动射流/被动射流2种点火方式,提出并论述了基于氨在线裂解制氢实现基于单一液氨燃料油箱的氨氢融合燃烧,是内燃机实现碳中和的极具潜力的技术路线,指出了氨氢内燃机喷雾、燃烧和氮基排放控制三方面需要解决的关键技术和科学问题。研究表明:氨氢融合内燃机采用微量氢气(小于3%)引燃氨混合气,可以获得稳定燃烧和高热效率,并拓展稀然极限。氨氢融合零碳大功率内燃机作为氨燃料高效可靠的应用载体,在重型车辆、工程机械、远洋船舶、发电等多个领域具备广泛的应用潜力与价值,氨氢内燃机的研发可推动基础燃烧理论的进步,也可以促进中国内燃机产业迈上新的台阶。

高电压下浓/稀天然气燃烧特性的对比研究

利用定容燃烧装置研究了高电压作用下浓/稀天然气火焰的燃烧特性,并探讨了以自由电子为主的阴离子对火焰燃烧的作用机理。试验中加载电压为0 kV、5 kV和10 kV,浓/稀混合气的过量空气系数λ分别为0.8和1.4。在加载电场作用下,球形膨胀火焰在与电场相反方向上的火焰传播明显加快,火焰传播速度和火焰拉伸率随加载电压的增强而增大,稀燃混合气的火焰传播的增强程度最为明显。加载10 kV电压时,λ为0.8和1.4火焰的平均速度比没有电场作用时分别增加了36.4%和49.5%。火焰传播速度的增强,促进了燃烧过程的进行,使得混合气燃烧的滞燃期缩短,压力升高率增加,且压力峰值时间提前。稀燃混合气的燃烧压力峰值有较大提高,而浓燃混合气的压力峰值变化不大。试验中加载电场对球形膨胀火焰燃烧的作用机理可用火焰中的阴离子,尤其是O-2主导的离子风效应来说明。同时,电场在一定程度上也促进了火焰燃烧化学反应的进行。

航空发动机核心机全三维数值仿真方法研究

利用流体分析软件ANSYS CFX,对航空发动机核心机进行了全三维流场数值仿真。采用出口边界模拟压气机级间引气和燃烧室二股气流流路,以及源项方法模拟涡轮叶片冷却喷射。考虑了压气机空腔效应、各叶片的端壁倒圆、转子叶片叶尖间隙等细节结构;燃烧室按照燃油喷雾模型计算化学反应。通过计算获得了核心机进口导流盆、压气机、燃烧室、涡轮及喷管的气动性能;分析整理出了部件各项参数沿径向的分布,获得了核心机推力,并与试验结果进行了对比。通过研究,初步校验了航空发动机核心机全三维数值仿真的可行性,为航空发动机整机全三维数值仿真奠定了技术基础。

燃烧化学动力学机理的框架简化：组分耦合的灵敏性分析简化方法（英文）

目的:发动机燃烧数值模拟需要高精度的、尺寸合适的化学反应机理,因此需要对复杂的详细化学反应机理进行简化。由于现有的灵敏性分析简化方法效率低且计算时间长,因此本文希望得出一种效率更高、计算时间更短的灵敏性分析简化方法。创新点:1.利用直接关系图简化方法中的相互作用系数计算待删除组分之间的相互耦合关系,提出了组分耦合的灵敏性分析简化方法;耦合关系较大的两个组分被视为一个整体,有助于提高灵敏性分析简化的效率、缩短计算时间。2.得到了较小尺寸的乙烯(33组分)和正庚烷(79组分)框架燃烧反应机理。方法:1.提出组分耦合的灵敏性分析简化方法,即先利用直接关系图简化方法中的相互作用系数计算待删除组分之间的相互耦合关系(公式(2)和(3),图2);在简化过程中,耦合关系较大的两个组分被视为一个整体被删除。2.通过0维和一维计算验证得到的简化化学反应机理的精度。结论:1.本文所提出的组分耦合的灵敏性分析简化方法提高了灵敏性分析简化的效率、缩短了计算时间。2.利用此方法对含有111组分和784基元反应的乙烯以及561组分和2539基元反应的正庚烷的燃烧化学机理进行简化,最终得到33组分的乙烯框架机理和79组分和339基元反应的正庚烷框架反应机理。3.在较宽的工况范围内对得到的框架机理进行点火延时、层流火焰传播速度、温度曲线、组分浓度和反应的灵敏性分析等燃烧特性参数的验证与分析,结果表明得到的框架机理具有较高的精度和较小的尺寸,适用于燃烧数值模拟。

PARALLELIZED UPWIND FLUX SPLITTING SCHEME FOR SUPERSONIC REACTING FLOWS ON UNSTRUCTURED HYBRID MESHES

A parallelized upwind flux splitting scheme for supersonic reacting flows on hybrid meshes is presented. The complexity of super/hyper-sonic combustion flows makes it necessary to establish solvers with higher resolution and efficiency for multi-component Euler/N-S equations. Hence, a spatial second-order van Leer type flux vector splitting scheme is established by introducing auxiliary points in interpolation, and a domain decomposition method used on unstructured hybrid meshes for obtaining high calculating efficiency. The numerical scheme with five-stage Runge-Kutta time step method is implemented to the simulation of combustion flows, including the supersonic hydrogen/air combustion and the normal injection of hydrogen into reacting flows. Satisfying results are obtained compared with limited references.

Investigation into Syngas Generation from Solid Fuel Using CaSO4-based Chemical Looping Gasification Process

Chemical-looping gasification （CLG） is a novel process for syngas generation from solid fuels, sharing the same basic principles as chemical-looping combustion （CLC）. It also uses oxygen carriers （mainly metal oxide and calcium sulfate） to transfer heat and oxygen to the fuel. In this paper, the primary investigation into the CLG process with CaSO4 as oxygen carrier was carried out by thermodynamic analysis and experiments in the tube reactor. Sulfur-contained gas emission was mainly H2S rather than SO2 in the CLG process, showing some different features from the CLC. The mass and heat balance of CLG processes were calculated thermodynamically to determinate the auto-thermal operating conditions with different CaSO4/C and steam/C molar ratios. It was found that the CaSO4/C molar ratio should be higher than 0.2 to reach auto-thermal balance. The effect of temperature on the reactions between oxygen carrier and coal was investigated based on Gibbs free energy minimum method and ex- perimental results. It indicated that high temperature favored the CLG process in the fuel reactor and part of syngas was consumed to compensate for auto-thermal system.

Modelling of Turbulent Nonpremixed CH4/H2 Flame Using Second-Moment Turbulence Closure Models

Turbulent nonpremixed CH4/H2 flame has been simulated using several typical differential secondmoment turbulence closure (SMTC) models. To clarify the applicability of the various models, the LRR-IP model,JM model, SSG model as well as two modified LRR-IP models were tested. Some of above-mentioned SMTC models cannot provide the overall satisfactory predictions of this challenging case. It is confirmed again that the standard LRR-IP model considerably overpredict the centerline velocity decay rate, and therefore performs not well. Also it is interesting to observe that the JM model does not perform well in this challenging test case, although it has already been proved successful in other cases. The SSG model produces quite satisfactory prediction and performs equally well or better than the two modified LRR-IP models in the reacting case. It can be concluded that the modified LRR-IP models as well as the SSG model are superior to the other SMTC models in the turbulent nonpremixed CH4/H2 flame.

Micro-organic dust combustion considering particles thermal resistance

Organic dust flames deal with a field of science in which many complicated phenomena like pyrolysis or devolatization of solid particles and combustion of volatile particles take place. One-dimensional flame propagation in cloud of fuel mixture is analyzed in which flame structure is divided into three zones. The first zone is preheat zone in which rate of the chemical reaction is small and transfer phenomena play significant role in temperature and mass distributions. In this model, it is assumed that particles pyrolyze first to yield a gaseous fuel mixture. The second zone is reaction zone where convection and vaporization rates of the particles are small. The third zone is convection zone where diffusive terms are negligible in comparison of other terms. Non-zero Biot number is used in order to study effect of particles thermal resistance on flame characteristics. Also, effect of particle size on combustion of micro organic dust is investigated. According to obtained results, it is understood that both flame temperature and burning velocity decrease with rise in the Biot number and particle size.

Exploring the Low-Temperature Oxidation Chemistry of Cyclohexane in a Jet-Stirred Reactor:an Experimental and Kinetic Modeling Study

We report the investigation on the low-temperature oxidation of cyclohexane in a jet-stirred reactor over 500-742 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry （SVUV-PIMS） was used for identifying and quantifying the oxidation species. Major products, cyclic olefins, and oxygenated products including reactive hydroperoxides and high oxygen compounds were detected. Compared with n-alkanes, a narrow low-temperature window （-80 K） was observed in the low-temperature oxidation of cyclohexane. Besides, a kinetic model for cyclohexane oxidation was developed based on the CNRS model [Combust. Flame 160, 2319 （2013）], which can better capture the experimental results than previous models. Based on the modeling analysis, the 1,5-H shift dominates the crucial isomerization steps of the first and second O2 addition products in the low-temperature chain branching process of cyclohexane. The negative temperature coefficient behavior of cyclohexane oxidation results from the reduced chain branching due to the competition from chain inhibition and propagation reactions, i.e. the reaction between cyclohexyl radical and O2 and the de- composition of cyclohexylperoxy radical, both producing cyclohexene and HO2 radical, as well as the decomposition of cyclohexylhydroperoxy radical producing hex-5-en-l-al and OH radical.

Analytical Model for Predicting the Heat Loss Effect on the Pyrolysis of Biomass Particles

This paper presents the combined influence of heat-loss and radiation on the pyrolysis of biomass particles by considering the structure of one-dimensional, laminar and steady state flame propagation in uniformly premixed wood particles. The assumed flame structure consists of a broad preheat-vaporization zone where the rate of gas-phase chemical reaction is small, a thin reaction zone composed of three regions: gas, tar and char combustion where convection and the vaporization rate of the fuel particles are small, and a broad convection zone. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large and the equivalence ratio is larger than unity(i.e.u≥1). The principal attention is made on the determination of a non-linear burning velocity correlation. Consequently, the impacts of radiation, heat loss and particle size as the determining factors on the flame temperature and burning velocity of biomass particles are declared in this research.

A novel model for cost performance evaluation of pulverized coal injected into blast furnace based on effective calorific value

The combustion process of pulverized coal injected into blast furnace involves a lot of physical and chemical reactions. Based on the combustion behaviors of pulverized coal, the conception of coal effective calorific value representing the actual thermal energy provided for blast furnace was proposed. A cost performance evaluation model of coal injection was built up for the optimal selection of various kinds of coal based on effective calorific value. The model contains two indicators: coal effective calorific value which has eight sub-indicators and coal injection cost which includes four sub-indicators. In addition, the calculation principle and application of cost performance evaluation model in a Chinese large-scale iron and steel company were comprehensively introduced. The evaluation results finally confirm that this novel model is of great significance to the optimal selection of blast furnace pulverized coal.

Numerical simulation of solid circulation mechanism and gas flow paths in a chemical looping combustion system

To study the gas-solid flow characteristics in a chemical looping combustion system integrated with a moving bed air reactor,a 3D full-loop numerical model was established using the Eulerian-Eulerian approach integrated with the kinetic theory of granular flow.The solid circulation mechanism and gas leakage performance were studied in detail.The simulation results showed that in the start-up process,the solid circulation rate first increased to approximately 5 kg/s and then dropped to approximately 1.2 kg/s;this observation was related to the dynamic control of the pressure distribution.In this system,the gas leakage between the inertial separator,upper air reactor,and lower air reactor was restrained by adjusting the pressure difference,thus obtaining optimal gas flow paths.When the pressures at the outlets of the inertial separator,upper air reactor,and lower air were 7.4,11.0,and 14.6 kPa,respectively,the gas leakage ratio was less than 1%in the system.

Experimental and Numerical Studies of Paraguayan Chaco Natural Gas in a Counterflow Diffusion Flame

Combustion is a chemical phenomenon in which a multitude of elementary chemical reactions take place, resulting in the overall process of fuel oxidation. Natural gas fuel has been explored for a few decades and extracted for a few years in the region of Paraguayan Chaco, near Bolivia border. Currently, natural gas is not very important in Paraguay＇s energy matrix, however it could be in the near future if higher volumes are extracted and transported to the most populated cities, specially to the capital. In order to improve Paraguayan natural gas combustion performance, an understanding of its fundamental properties and the combustion pathways is required. This study presents new data for Paraguayan Chaco natural gas combustion in a laminar counterflow diffusion flame configuration at atmospheric pressure. Visible chemiluminescence of excited radicals CH＊ and C2^＊ is employed experimentally. 1D numerical simulation was carried out using Paraguayan Chaco natural gas chemical composition and a standard kinetic mechanism, to which we added CH＊ and C] reactions. Typical flame structures resulting from simulation are presented and a validation of the model is realized comparing experimental and numerical CH＊ and C~ radicals profiles.

Effect of hydrogen combustion reaction on the dehydrogenation of ethane in a fixed-bed catalytic membrane reactor

A two-dimensional non-isothermal mathematical model has been developed for the ethane dehydrogenation reaction in a fixed-bed catalytic membrane reactor. Since ethane dehydrogenation is an equilibrium reaction,removal of produced hydrogen by the membrane shifts the thermodynamic equilibrium to ethylene production.For further displacement of the dehydrogenation reaction, oxidative dehydrogenation method has been used.Since ethane dehydrogenation is an endothermic reaction, the energy produced by the oxidative dehydrogenation method is consumed by the dehydrogenation reaction. The results show that the oxidative dehydrogenation method generated a substantial improvement in the reactor performance in terms of high conversions and signi ficant energy saving. It was also established that the sweep gas velocity in the shell side of the reactor is one of the most important factors in the effectiveness of the reactor.

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 highfidelity combustion simulation.This paper reviews the current status of the state-of-the-art large eddy simulation(LES)/probability 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.

Simulation of a Shock Tube with a Small Exit Nozzle

Shock tubes are frequently used to rapidly heat up reaction mixtures to study chemical reaction mechanisms and kinetics in the field of combustion chemistry [1]. In the present work, the flow field inside a shock tube with a small nozzle in the end plate has been investigated to support the analysis of reacting chemical mixtures with an attached mass spectrometer and to clarify whether the usual assumptions for the flow field and the related ther- modynamics are fulfilled. In the present work, the details of the flow physics inside the tube and the flow out of the nozzle in the end plate have been investigated. Due to the large differences in the typical length scales and the large pressure ratios of this special device, a very strong numerical stiffness prevails during the simulation process. Second-order ROE numerical schemes have been employed to simulate the flow field inside the shock tube. The simulations were performed with the commercial code ANSYS Fluent [2]. Axial-symmetric boundary conditions are employed to reduce the consumption of CPU time. A density-based transient scheme has been used and vali- dated in terms of accuracy and efficiency. The simulation results for pressure and density are compared with ana- lytical solutions. Numerical results show that a density-based numerical scheme performs better when dealing with shock-tube problems [5]. The flow field near the nozzle is studied in detail, and the effects of the nozzle to pressure and temperature variations inside the tube are invcstigatcd. The results show that this special shock-tube setup can be used to study high-temperature gas-phase chemical reactions with reasonable accuracy.

A Chemical Reactor Network for Oxides of Nitrogen Emission Prediction in Gas Turbine Combustor

This study presents the use of a new chemical reactor network(CRN) model and non-uniform injectors to predict the NOx emission pollutant in gas turbine combustor. The CRN uses information from Computational Fluid Dynamics(CFD) combustion analysis with two injectors of CH4-air mixture. The injectors of CH4-air mixture have different lean equivalence ratio, and they control fuel flow to stabilize combustion and adjust combustor's equivalence ratio. Non-uniform injector is applied to improve the burning process of the turbine combustor. The results of the new CRN for NOx prediction in the gas turbine combustor show very good agreement with the experimental data from Korea Electric Power Research Institute.