基于浓度敏感性分析和遗传算法的甲烷燃烧机理简化与优化

采用良搅拌反应器模型和层流预混火焰模型计算甲烷/空气燃烧过程,通过元素流通法和浓度敏感性分析法,对甲烷燃烧详细化学动力学机理GRIMECH 3.0进行简化。利用遗传算法,以甲烷/空气详细机理获得的组分浓度和一维层流火焰速度为目标,对简化机理进行优化。结果表明,相比于优化之前的简化机理,优化后的简化机理在描述甲烷/空气燃烧反应的组分浓度、层流火焰速度以及反应物和产物的时空分布方面,具有更高的精度。     

基于重要性分析的甲烷/乙烯混合燃烧框架机理构筑

建立了基于重要性分析的详细化学机理分析平台,利用耦合组分化学存活时间和敏感性系数的重要性参数,确定详细机理中的准稳态组分,通过移除这些组分及其相关反应,得到了计算精度较高的框架机理。针对目前燃烧学界较为关注的混合燃烧问题,以甲烷、乙烯这两种典型低碳碳氢燃料为研究对象,对其详细化学反应机理进行了分析,利用重要性分析法构筑框架机理,并对甲烷/空气和甲烷/乙烯/空气预混火焰进行了数值计算。与详细机理相比,框架机理所涉及的组分数与基元反应数都得到了大幅度的降低,计算时间明显减少,但对火焰温度及反应物、生成物、中间组分浓度的预测与采用详细机理得到的结果吻合良好,证明了重要性分析法的有效性与可靠性。     

飞机防火试验中的燃烧反应动力学模型研究

使用反应路径分析法对Jet-A型航空煤油燃烧的气相燃烧机理进行简化。选用POSF-4658机理作为Jet-A燃烧的详细反应机理,该机理包含1607种燃烧组分、6633个基元反应机理。将飞机防火试验条件作为简化过程的初始条件,得到78种组分,196个反应机理的Jet-A燃烧机理。通过对Jet-A的简化反应机理、详细反应机理和JetA实验数据的比较可以发现,简化反应机理可以较准确地反映Jet-A型航空煤油在防火试验条件下的燃烧特性。利用常用的Jet-A型航空煤油简化机理计算的绝热火焰温度、点火延迟时间及层流火焰速度与本文提出的简化的计算值进行比较。结果表明,提出的简化机理在防火试验条件下具有较高的精确度。得到的Jet-A简化反应机理可为飞机防火试验的仿真研究提供燃烧场的化学反应动力学模型。     

利用主成分分析法简化甲烷/空气层流预混火焰的反应机理

利用主成分分析(Principal Component Analysis)的方法对甲烷/空气氧化的详细化学反应机理进行了简化，在低压层流预混火焰条件下进行了计算，计算结果与详细机理的计算结果及实验值进行了比较。结果表明简化机理与详细机理吻合较好，简化机理的规模和计算时间有所减少。     

基于连通法的甲烷简化机理构筑研究

采用连通法,针对甲烷复杂反应机理,成功地进行了不同水平的机理简化研究。通过建立组分依赖关系的正规化Jacobian矩阵,精确地查明了燃烧组分之间的耦合关系,分别构造出仅包含重要化学路径的两个动力学简化模型,获得的简化机理分别包含227和138个反应,分别涉及39和26种组分。通过对层流预混火焰结构的模拟,所得简化机理和原详细反应动力学机理关于火焰结构的计算吻合很好,计算结果显示,两个简化机理具有较高的模拟精度。     

DME简化反应模型及其在HCCI燃烧分析中的应用研究

提出了一个可应用于HCCI发动机工作过程研究的DME化学反应动力学简化模型,该模型由28种组分、38个基元反应组成,包括3个子模型,即低温反应和负温度系数区子模型、高温裂解和高温氧化子模型以及甲酸生成过程子模型.通过算例对比分析,该DME简化模型能正确揭示DME燃烧过程主要生成物组分的变化规律,能准确计算DME燃烧过程低温和高温阶段的放热特征时刻,其计算结果与详细机理计算结果吻合.相对于详细机理,简化模型节省了计算时间,为实现化学反应动力学与CFD多维模型耦合的燃烧计算提供了一个可行而有效的途径.     

针对C3H8／空气扩散火焰的PCA简化机理构筑

C3H8是液化石油气（LPG）的主要成分,其火焰结构的数值预测对于消防等相关行业具有重要意义。单步或总包反应过于简单,不能描述碳氢燃料的氧化机制,而耦合燃料详细机理的燃烧模拟计算量大,且描述反应的数学系统具有极强的“刚性”,限制了反应机理的实际应用,而去除冗余反应和组分的简化机理具有描述燃烧的全面性优点,且降低了数学系统的“刚性”,因此耦合简化机理的火焰结构数值预测具有优势。本文采用基于矩阵分析的主成分（PCA）分析技术,分析研究了wang等发展的469步C3H8详细反应动力学机理,获得了组分的重要性排序,基于此分别构筑了320步和214步两个简化机理,针对典型扩散火焰的计算,表明建立的两个简化机理具有较高的模拟可靠性,同时也提供了一种框架简化机理的构筑方法。     

乙醇及自由基引导对甲烷预混火焰结构影响的数值模拟

本文使用了详细化学反应动力学机理计算模拟了混合有乙醇及典型自由基引导的甲烷预混火焰结构.该反应机理由Marinov研究组研究发表,包含有56个组分以及372个反应.本文的计算使用了CHEMKIN-3以及预混火焰代码,热力学及输运部分的计算基于Sandia国家实验室和Marinov研究室发布的数据库.火焰结构中主要产物的变化,关键中间产物和次要组分的计算结果显示加入乙醇和自由基都可以减少着火延迟.本文计算了三种不同条件下的火焰结构,分别为预混CH4/O2/N2火焰;预混甲烷/乙醇火焰;和加入引导自由基在甲烷/乙醇混合燃料中.此外还有含有自由基的甲烷火焰和加入乙醇的甲烷火焰比较.     

氢气爆炸特性研究

本文研究、总结了氢气与空气(氢气与氧气)的混合物的爆炸特性.即氢气在空气中,在比较低燃烧界限的情况下,只有向上的传播和非常少的超压可以观测得到.正因为氢气的这种特性,将氢应用于科技将极大地推进社会进步,氢燃料将成为一种主要的能源.然而,氢技术应用的成功与否主要取决于氢使用的安全性.所以,必须掌握实际使用时氢气燃烧的性能.本文在日本过去十年实验数据的基础上,通过实验研究了氢气与空气混合物的燃点.研究了氢气、氧气混合物经氮气稀释后,按化学当量比例将不同浓度的氢气与空气进行混合,并得出了低温下的爆炸压力特性.随后,分别讨论了在初始压力下一致的情况下,试管直径相同的状况下,氢气与空气混合浓度相同的情况下,这三种爆轰传播限制之间的关系.得出了在空气中直接点燃的发生爆轰的最小试管直径,最小的装药量之间的关系,进行了爆轰危险性分级.最后,文章概括比较了氢与其他燃料的燃烧特性,评估了氢气燃烧过程中的危险与安全因素.     

膨胀聚苯乙烯热分解动力学分析和寿命预测

针对既有聚苯乙烯泡沫类外墙外保温系统的防火问题,在空气和氮气气氛下对非阻燃和阻燃型膨胀聚苯乙烯泡沫进行了热重分析。样品由10℃/min、20℃/min、40℃/min和50℃/min四个升温速率从室温加热至800℃。热分解动力学参数由Flynn-Wall-Ozawa(FWO)等转化率方法和多参数非线性回归方法(multivariate non-linear re-gression method)计算,结果表明六溴环十二烷(HBCD)阻燃剂可一定程度上提高EPS的热稳定性。EPS在空气和氮气气氛下热解可认为是单步反应。非阻燃聚苯乙烯泡沫在空气和氮气气氛下的热解过程可由自催化n阶反应机理描述。阻燃EPS在空气气氛下的热解机理为自催化n阶反应,在氮气气氛下则为n阶反应机理。基于动力学参数和反应机理,对聚苯乙烯泡沫在不同温度下的寿命进行了预测。     

Self-ignition in stone wool insulation contaminated with fatty acid (fundamentals,case study,analysis methodology)

A combination of a residual film of flammable organic substance, air and porous structures like insulation material (e.g. stone wool) may result in a fire. The initiating self-heating process depends on the substance (reactivity, volatility), amount of accumulated liquid, volume and temperature. Specific information is given for application and extension of the Thomas criterion with a 2nd order reaction. The experimental part includes new experimental techniques to determine heat transfer and formal reaction kinetic data. The applied self-ignition temperature (SIT) simulation model relies on liquid film volume and not on liquid film surface reaction. As a further result of the studies detailed working procedure of three simplified methodologies for estimation of SITs in technical scale are presented. New techniques to determine parameters necessary for SIT prediction, especially in combination with Methodology III, have the power to reduce the costs for estimating the SIT up to 80%.     

车载储氢瓶泄漏及车库内通风方式研究*

为研究车库内燃料电池汽车氢气意外泄漏后的浓度分布情况,采用ANSYS软件,通过分析可燃性气体体积、水平方向和垂直方向氢气的扩散分布、不同泄漏位置氢气的扩散情况,研究6种不同通风方式对氢气意外泄漏扩散分布的影响,针对车库内氢气泄漏的特性,在通风方式上引入侧墙底部送风和侧墙顶部送风方式。研究结果表明:底部送风能显著加快氢气的扩散和排出。垂直高度上氢气浓度分布不均,侧墙顶部送风能使顶部堆积的氢气向下扩散,降低最大气体浓度;在墙角泄漏会由于墙壁的影响导致氢气堆积,对墙角局部通风尤为重要。研究结果可为氢燃料电池汽车专用车库的通风设计提供重要参考。     

Determination of heterogeneous reaction mechanisms: A key milestone in dust explosion modelling

Reaction kinetics is fundamental for modelling the thermal oxidation of a solid phase, in processes such as dust explosions, combustion or gasification. The methodology followed in this study consists in i) the experimental identification of the reaction mechanisms involved in the explosion of organic powders, ii) the proposal of simplified mechanisms of pyrolysis and oxidation, iii) the implementation of the model to assess the explosion severity of organic dusts. Flash pyrolysis and combustion experiments were carried out on starch (22 μm) and cellulose (53 μm) at temperatures ranging from 973 K to 1173 K. The gases generated were collected and analyzed by gas chromatography. In this paper, a semi-global pyrolysis model was developed for reactive systems with low Damköhler number. It is in good agreement with the experimental data and shows that both carbon monoxide and hydrogen are mainly generated during the pyrolysis of the solid, the generation of the latter compound being greatly promoted at high temperature. A simplified combustion model was also proposed by adding two oxidation reactions of the pyrolysis products. In parallel, flame propagation tests were performed in a semi open tube in order to assess the burning velocity of such compounds. The laminar burning velocity of cellulose was determined to be 21 cm s⁻¹. Finally, this model will be integrated to a predictive model of dust explosions and its validation will be based on experimental data obtained using the 20 L explosion sphere. The explosion severity of cellulose was determined and will be used to develop and adjust the predictive model.     

Explosion limits of mixtures relevant to the production of 1,2-dichloroethane (ethylene dichloride)

A simple method exists to estimate the limiting oxygen concentration (LOC) based upon the lower explosion limit (LEL) by assuming (1) that the LOC lies at the apex of the explosion area, (2) that the LEL is unaffected by nitrogen addition and (3) that the apex of the explosion area lies on the stoichiometric line. This estimation method is assessed for mixtures relevant to the production of 1,2-dichloroethane. To this end, the explosion areas of ethylene/hydrogen/nitrogen/air, ethylene/nitrogen/air and ethylene/1,2-dichloroethane/hydrogen chloride/nitrogen/air mixtures are determined at typical process conditions. The experiments are performed in a closed spherical 8 l vessel. The mixtures are ignited by fusing a coiled tungsten wire, placed at the centre of the vessel. A 5% pressure rise criterion is used to determine the explosion limits. The experimental procedure is based upon EN 14756. It is found that a safe estimate of the LOC of ethylene/hydrogen/nitrogen/air mixtures can be found based upon the LEL of these mixtures.     

Analysis of gas dispersion and ventilation within a comprehensive CAD model of an offshore platform via computational fluid dynamics

Maintaining an adequate air flow with a desired air quality that is free from hazardous gases is among the most important actions taken toward the improvement of safety in any process plant. Due to the increased focus on the consequences of existing hazardous material on safety, health, and the environment, air quality and sufficient ventilation within a plant has been increasingly considered in the design stage. This paper investigates and analyzes methane and hydrogen sulfite dispersion and the effect of air ventilation within a CAD model of an offshore platform using computation fluids dynamics (CFD). In addition, this method and its principals could be utilized in any other hazardous environment. Simulations of possible hazardous events along with solutions for preventing or reducing their probability are presented to better assess the data. These investigations are performed by considering hypothetical hazardous scenarios which consist of gas leakages from pipes and process equipment under different conditions. After drafting a precise and highly detailed CAD model of the plant and performing CFD simulations on this model, the results of gas behaviors, dispersion, distribution, accumulation, and its possible hazards are investigated and analyzed. The larger amount of details of the actual plant model in CFD simulation are obtained by using a combination of different methods and software. These include PDMS for 3-D drawing of the plan, Rinoceros for geometrical integration of the process equipment and facilities, and Sharc Harpoon which meshes the model. Moreover, the probability of inducing ignitable or toxic concentration of gases within the atmosphere and air ventilation of the unit is considered by these investigations.     

Thermal hazard in a batch process involving hydrogen peroxide

Hydrogen peroxide is a versatile and interesting reagent for many industrial processes; nevertheless, it is very sensitive to impurities that can catalyze its decomposition, so that the desired reaction could be accompanied by undesired parallel and consecutive reactions. As an example, the butadiene free radical polymerization with hydrogen peroxide in the presence of an organic solvent was studied. Batch polymerization occurs in the liquid phase at about 120 °C. Because of the involved reactive compounds and the relatively high temperature, this is an intrinsically dangerous reaction. Therefore calorimetric data can give important information about safety and process optimization during the scale-up. The aim of this research project was to study the influence of impurities on the overall heat of reaction. The experiments were made in a high-pressure reaction calorimeter. The study has revealed that impurities do indeed affect the reaction course. Most importantly, the presence of carboxylic acids and/or ionic iron must be avoided and the recycle of unreacted reagents must be carefully controlled to minimize the build-up of these impurities.