十氢萘/空气混合物高温着火延迟的激波管测量

在激波管上进行了气相十氢萘/空气混合物的着火延迟测量, 着火温度为950-1395 K, 着火压力为1.82×10⁵-16.56×10⁵ Pa, 化学计量比分别为0.5、1.0 和2.0. 在侧窗处利用反射激波压力和CH^*发射光来测出着火延迟时间. 系统研究了着火温度、着火压力和化学计量比对十氢萘着火延迟时间的影响. 实验结果显示着火温度和着火压力的升高均会缩短着火延迟时间. 首次在相对高和低压的条件下观察到了化学计量比对十氢萘着火延迟的影响是完全相反的. 当压力为15.15×10⁵ Pa时, 富油混合物呈现出最短的着火延迟时间, 而贫油混合物的着火延迟时间却是最长的. 相反, 当压力为2.02×10⁵ Pa时, 富油混合物的着火延迟时间最长. 着火延迟数据与已有的动力学机理的预测值进行对比, 结果显示机理在所有的实验条件下均很好地预测了实验着火延时趋势. 为了探明化学计量比对着火延迟时间影响的本质, 对高、低压条件下的着火延时进行了敏感度分析.结果显示, 压力为2.02×10⁵ Pa时, 控制着火延迟的关键反应为H+O₂=OH+O, 而涉及十氢萘及其相应自由基的反应在15.15×10⁵ Pa时对着火延迟起主要作用.     

煤油裂解产物/空气与煤油/空气在宽温度范围内点火延迟的对比研究

Kerosene is an ideal endothermic hydrocarbon. Its pyrolysis plays a significant role in the thermal protection for high-speed aircraft. Before it reacts, kerosene experiences thermal decomposition in the heat exchanger and produces cracked products. Thus, to use cracked kerosene instead of pure kerosene, knowledge of their ignition properties is needed. In this study, ignition delay times of cracked kerosene/air and kerosene/air were measured in a heated shock tube at temperatures of 657–1333 K, an equivalence ratio of 1.0, and pressures of 1.01 × 10⁵–10.10 × 10⁵ Pa. Ignition delay time was defined as the time interval between the arrival of the reflected shock and the occurrence of the steepest rise of excited-state CH species (CH*) emission at the sidewall measurement location. Pure helium was used as the driver gas for high-temperature measurements in which test times needed to be shorter than 1.5 ms, and tailored mixtures of He/Ar were used when test times could reach up to 15 ms. Arrhenius-type formulas for the relationship between ignition delay time and ignition conditions (temperature and pressure) were obtained by correlating the measured high-temperature data of both fuels. The results reveal that the ignition delay times of both fuels are close, and an increase in the pressure or temperature causes a decrease in the ignition delay time in the high-temperature region (> 1000 K). Both fuels exhibit similar high-temperature ignition delay properties, because they have close pressure exponents (cracked kerosene: τ_ign∝P^-0.85; kerosene:τ_ign∝P^-0.83) and global activation energies (cracked kerosene: E_a = 143.37 kJ·mol^-1; kerosene: E_a = 144.29 kJ·mol^-1). However, in the low-temperature region (< 1000 K), ignition delay characteristics are quite different. For cracked kerosene/air, while the decrease in the temperature still results in an increase in the ignition delay time, the negative temperature coefficient (NTC) of ignition delay does not occur, and the low-temperature ignition data still can be correlated by an Arrhenius-type formula with a much smaller global activation energy compared to that at high temperatures. However, for kerosene/air, this NTC phenomenon was observed, and the Arrhenius-type formula fails to correlate its low-temperature ignition data. At temperatures ranging from 830 to 1000 K, the cracked kerosene ignites faster than the kerosene; at temperatures below 830 K, kerosene ignition delay times become much shorter than those of cracked kerosene. Surrogates for cracked kerosene and kerosene are proposed based on the H/C ratio and average molecular weight in order to simulate ignition delay times for cracked kerosene/air and kerosene/air. The simulation results are in fairly good agreement with current experimental data for the two fuels at high temperatures (> 1000 K). However, in the low-temperature NTC region, the results are in very good agreement with kerosene ignition delay data but disagree with cracked kerosene ignition delay data. The comparison between experimental data and model predictions indicates that refinement of the reaction mechanisms for cracked kerosene and kerosene is needed. These test results are helpful to understand ignition properties of cracked kerosene in developing regenerative cooling technology for high-speed aircraft.     

戊酸甲酯高温点火的激波管研究

戊酸甲酯是生物柴油和长链脂类燃烧过程中的中间产物之一。迄今为止,文献中还没有戊酸甲酯点火延迟的实验结果,因此对其点火特性的研究是必要的。在本文工作中,于反射激波后测量了戊酸甲酯/空气和戊酸甲酯/4%氧气/氩气的点火延迟时间。实验条件为:戊酸甲酯/空气点火温度1050–1350 K,点火压力1.5 × 10⁵和16 × 10⁵ Pa,当量比0.5、1和2;戊酸甲酯/4%氧气/氩气点火温度1210–1410 K,点火压力3.5 × 10⁵和7 × 10⁵ Pa,当量比0.75和1.25。点火延迟时间由在距离激波管端面15毫米处的测量点测到的反射激波到达信号和CH自由基信号所决定。所得实验结果显示：对于戊酸甲酯/空气和戊酸甲酯/4%氧气/氩气,温度或压力的增加都一定会使它们的点火延迟时间变短,但对于戊酸甲酯/空气,当量比对其点火延迟时间的影响在高低压下却是不同的(16 × 10⁵ Pa: τ_ign = 5.43 × 10⁻⁶Ф^−0.411exp(1.73 × 10²/RT),1.5 × 10⁵ Pa: τ_ign = 7.58 × 10⁻⁷Ф^0.193exp(2.11 × 10²/RT)。当压力为3.5 × 10⁵–7 × 10⁵ Pa时,还获得了戊酸甲酯/4%氧气/氩气点火延迟时间随点火条件的变化关系：τ_ign = 2.80 × 10⁻⁵(10⁻⁵P)^{−0.446±0.032}Ф^0.246±0.044exp((1.88 ± 0.03) × 10²/RT)。这些关系式反映了点火延迟时间对温度、压力和当量比的依赖关系,且有助于将实验数据归一到特定条件下进行比较。在本文实验条件下,由于戊酸甲酯/空气的燃料浓度远大于戊酸甲酯/4%氧气/氩气的燃料浓度,所测戊酸甲酯/空气的点火延迟时间远短于戊酸甲酯/4%氧气/氩气的点火延迟时间。通过对戊酸甲酯和其它长链脂类的点火特性比较,发现在相对低温时(空气中1200 K以下,氩气中1280 K以下),戊酸甲酯的点火延迟时间要长于其它长链脂类的点火延迟时间。已有的两个戊酸甲酯化学动力学机理都不能很好地预测本文实验结果,对戊酸甲酯机理的进一步完善是需要的。敏感度分析结果表明,支链反应H + O₂ = O + OH对戊酸甲酯的高温点火起着最强的促进作用。据我们所知,本文首次报道了戊酸甲酯的高温点火延迟实验数据,研究结果对了解戊酸甲酯的点火特性非常重要,并且为完善戊酸甲酯的化学动力学机理提供了实验依据。     

正癸烷着火及燃烧的化学动力学模型

构建了一个包含46组分和167反应的描述正癸烷着火与燃烧过程的化学反应动力学机理模型, 该机理是在通过路径分析和灵敏度分析对Peters 机理(118组分和527反应)进行较大程度简化的基础上, 对低温着火和火焰传播速度影响较大的部分基元反应进行修正和改进后得到的. 与文献给出的实验结果对比表明, 该机理不仅比现有的机理具有较少的组分数和基元反应数, 而且能够更准确地预测正癸烷低温和高温条件下的着火延迟时间和火焰传播速度. 该机理为进一步实现总包简化机理与计算流体力学(CFD)的耦合计算奠定了基础.     

基于激波管装置的乙烯氧化实验研究与动力学机理分析

在乙烯/氧气化学计量比为1,温度1092-1743 K,压力1.3-3.0 atm (1 atm = 101325 Pa)范围内,利用激波管测量了在摩尔分数为96%和75%两种不同氩气稀释度工况下的乙烯/氧气/氩气反应体系的着火延迟时间。实验结果表明,乙烯着火延迟时间在低稀释度下比高稀释度下短,着火延迟时间的对数与温度的倒数成良好线性关系,随着温度增加着火延迟时间缩短。此外,低稀释度下,能观察到爆轰(或者爆燃转爆轰)现象,而在高稀释度下,未发生爆轰现象。将四种不同机理模拟结果与实验结果比较,发现LLNL机理与实验结果吻合得较好。反应路径分析研究表明,稀释度对乙烯氧化反应路径无影响,而温度影响较大,温度增加,乙烯消耗路径由四条减少为三条,反应C₂H₄ + H (+ M) = C₂H₅ (+ M)由正向消耗乙烯变为逆向生成乙烯。     

氢气对正丁烷/空气混合物催化着火的热作用和化学作用

通过对正丁烷/氢气/空气混合物在Pt 催化表面的详细反应机理分析, 研究了氢气添加对正丁烷/空气混合物催化着火过程的影响. 研究发现, 在正丁烷/空气混合中添加氢气有助于正丁烷在更低的温度下实现催化着火, 而且不同的氢气添加量对混合物的着火温度和着火过程呈现不同的影响: 当氢气添加量较小时, 氢气的作用主要呈现为热影响; 而当氢气添加量较大时, 氢气的作用主要呈现为化学影响. 这些结果与实验结果是一致的. 本文进一步确定了发挥不同作用的氢气添加量的范围, 并分别对热作用和化学作用情况下的着火启动反应进行了动力学分析.     

四氯合镉酸正十一烷铵的合成、晶体结构及低温热容

合成了四氯合镉酸正十一烷铵配合物(C₁₁H₂₃NH₃)₂CdCl₄(s)[简写: C₁₁Cd(s)]. 用X 射线单晶衍射技术、化学分析和元素分析确定其晶体结构和化学组成. 利用其晶体学数据计算出晶格能为: U_POT＝908.18 kJ·mol^-1. 利用精密自动绝热热量计测定了它在78～395 K 温区的低温热容, 结果表明, 该配合物在此温区出现两次连续的固-固相转变, 计算出两次相变的峰温、摩尔焓及摩尔熵分别为: T_trs,1＝(321.88±0.07) K, Δ_trsH_m,1＝(37.59±0.17) kJ·mol^-1, Δ_trsS_m,1＝(117.24±0.12) J·K^-1·mol^-1, T_trs,2＝(323.81±0.30) K, Δ_trsH_m,2＝(12.42±0.02) kJ·mol^-1 和Δ_trsS_m,2＝(38.36±0.09) J·K^-1·mol^-1. 用最小二乘法将实验摩尔热容对温度进行拟合, 得到热容随温度变化的多项式方程. 用此方程进行数值积分,得到此温区每隔5 K 的舒平热容值和相对于298.15 K 时的热力学函数值.     

石墨烯/正十八烷微胶囊的制备与及其热性能研究

以石墨烯/正十八烷为芯材,三聚氰胺-尿素-甲醛树脂(MUF)为壁材,苯乙烯马来酸酐共聚物(SMA)为乳化剂,采用乳液聚合法制备相变微胶囊.系统研究了石墨烯对于正十八烷微胶囊性能的影响.采用场发射扫描电子显微镜(FE-SEM)、傅里叶变换红外光谱分析仪(FTIR)、拉曼光谱仪、X射线衍射仪(XRD)、Hot Disk热常数分析仪、示差扫描量热仪(DSC)和热重分析仪(TGA)对相变微胶囊的外貌形态、晶型结构和热性能进行表征和分析.结果表明,微胶囊呈圆球形且光滑,粒径约为1~30μm.当石墨烯添加量为0.1 g时,微胶囊的形貌无明显变化.当加入过量石墨烯时,微胶囊出现了明显的团聚现象.XRD测试表明,包覆于微胶囊中的石墨烯没有使微胶囊的结晶峰位置发生明显的偏移,这对于微胶囊的实际应用是有利的.微胶囊的相变热焓和包覆率随着石墨烯的加入而不断减小,但芯材的过冷现象得到了明显的改善.石墨烯对于微胶囊传热性能的提升有着显著的效果.当石墨烯的添加量为0.2 g时,微胶囊的导热系数为0.092 W·m-1·K-1,与纯微胶囊相比提高了约51%,这说明石墨烯改善了传统相变微胶囊的传热性能,提升了相变微胶囊的应用性能.     

高温非平衡条件下氟原子亲电动力学的激波管研究

To study electron affinity kinetics, a shock tube method was applied, in which the test gas was ionized by a reflected shock wave and subsequently quenched by a strong rarefaction wave. As the quenching speed of 106 K/s was reached, a nonequilibrium ionization recombination process occurred, which was dominated by ion recombination with electrons. A Langmuir electrostatic probe was used to monitor variation in the ion number density at the reflection shock region. The working state of the probe was analyzed, and a correction was introduced for reduction of the probe current due to elastic scattering in the probe sheath. The three body electron affinity rate coefficient of the fluorine atom over the temperature range 1200 to 2200 K in an ambiance of argon gas was directly determined. The temperature dependence of electron affinity rate coefficient was discussed.     

煤油裂解产物/空气与煤油/空气在宽温度范围内点火延迟的对比研究（英文）

煤油是一种理想的吸热性碳氢燃料,其热裂解在高速飞行器的热防护中起着重要作用。本工作利用加热激波管测量了煤油裂解产物/空气和煤油/空气的点火延时,点火温度657–1333 K,化学计量比1.0,点火压力1.01×10~5–10.10×10~5Pa。通过对高温点火延时数据的拟合获得了两种混合物关于点火延时间和点火条件(温度和压力)的Arrhenius型关系。测量结果显示,在高温区( 1000 K)两种混合物的点火延时很接近,并且点火延时随着温度或压力的增加而变短。但在低温区(1000 K),两种混合物的点火延迟特性却非常不同。煤油裂解产物的点火延时在此低温区域仍然随着温度的减小而增长,没有出现着火延迟的负温度效应;煤油的点火延迟在此温度区域却表现出明显的负温度效应。在830–1000 K温度区间,煤油裂解产物的点火延时快于煤油的;当温度低于830K时,煤油的点火延迟时却变得比煤油裂解产物的快很多。本实验结果与机理模拟结果的比较显示,对煤油裂解产物和煤油燃烧反应机理的完善是必要的。本研究结果对了解煤油裂解产物的点火延迟特性和发展高速飞行器再生冷却技术非常有帮助。     

JP-10点火延时的激波管研究

JP-10 (exo-tetrahydrodicyclopentadiene, C10H16) ignition delay times were measured in a preheated shock tube. The vapor pressures of the JP-10 were measured directly by using a high-precision vacuum gauge, to remedy the difficulty in determining the gaseous concentrations of heavy hydrocarbon fuel arising from the adsorption on the wall in shock tube experiments. The whole variation of pressure and emission of the OH or CH radicals were observed in the ignition process by a pressure transducer and a photomultiplier with a monochromator. The emission of the OH or CH radicals was used to identify the time to ignition. Experiments were performed over the pressure range of 151-556 kPa, temperature range of 1000-2100 K, fuel concentrations of 0.1%-0.55% mole fraction, and stoichiometric ratios of 0.25, 0.5, 1.0 and 2.0. The experimental results show that for the lower and higher temperature ranges, there are different dependency relationships of the ignition time on the temperature and the concentrations of JP-10 and oxygen.     

Shock Tube Measurement of Ethylene Ignition Delay Time and Molecular Collision Theory Analysis

In this study, 75% and 96% argon diluent conditions were selected to determine the ignition delay time of stoichiometric mixture of C₂H₄/O₂/Ar within a range of pressures (1.3-3.0 atm) and temperatures (1092-1743 K). Results showed a logarithmic linear relationship of the ignition delay time with the reciprocal of temperatures. Under both two diluent conditions, ignition delay time decreased with increased temperature. By multiple linear regression analysis, the ignition delay correlation was deduced. According to this correlation, the calculated ignition delay time in 96% diluent was found to be nearly five times that in 75% diluent. To explain this discrepancy, the hard-sphere collision theory was adopted, and the collision numbers of ethylene to oxygen were calculated. The total collision numbers of ethylene to oxygen were 5.99×10³⁰ s^-1cm^-3 in 75% diluent and 1.53×10²⁹ s^-1cm^-3 in 96% diluent (about 40 times that in 75% diluent). According to the discrepancy between ignition delay time and collision numbers, viz. 5 times corresponds to 40 times, the steric factor can be estimated.     

煤油自点火特性的实验研究

在加热激波管中利用反射激波点火,采用壁端压力和CH*发射光作为点火指示信号,测量了气相煤油/空气混合物的点火延时,点火温度为1100-1500K,压力为2.0×105和4.0×105Pa,化学计量比(Φ)为0.2、1.0和2.0.分析了点火温度、压力和化学计量比对点火延时的影响.结果显示,化学计量比为1.0和2.0时活化能几乎是相同的,但与化学计量比为0.2时的活化能差异很大,拟合得到了不同化学计量比条件下点火延时随温度变化的关系式.点火延时与已有的动力学机理进行对比,实验结果与Honnet等人的动力学机理吻合得很好.对不同化学计量比条件下的反应进行了敏感度分析,结果表明在化学计量比为0.2时,对点火延时敏感的关键反应与化学计量比为1.0时的有很大差异.     

正癸烷燃烧机理及航空煤油点火延时动力学模拟

以单一正癸烷作为国产航空煤油的单组分替代模型, 应用自有的碳氢燃料反应机理生成程序ReaxGen-Combustion构建了燃烧反应的详细机理. 以国产煤油在加热型激波管上的燃烧实验为参考, 对比研究了文献报道的3组分替代模型(模型Ⅰ)、2组分替代模型(模型Ⅱ)以及本文的单组分替代燃烧反应机理(模型Ⅲ)在预测我国航空煤油点火延时特性方面的实用性. 结果表明, 温度在1052~1538 K时, 模型Ⅰ预测的点火延时与实验值相差较大; 模型Ⅲ在温度高于1176 K时的预测值与实验值符合较好, 在1052~1176 K之间时则相差较大; 模型Ⅱ与模型Ⅲ预测值符合很好, 由于前者考虑了低温反应机理, 因而对1052~1176 K区间的预测精度与模型Ⅲ相比有所改善. 计算还发现, 模型Ⅱ中添加的20%(质量分数)1,2,4-三甲基苯对高温段点火延时未产生明显影响.     

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.     

Analysis on First-stage Ignition of n-Heptane at Low Temperatures with a Lumped Skeletal Mechanism

Two-stage ignition exists in the low-temperature combustion process of n-heptane and the first-stage ignition also shows a negative temperature coefficient(NTC) phenomenon. To study key reactions and understand chemical principles affecting the first-stage ignition of n-heptane, a lumped skeletal mechanism with 62 species is obtained based on the detailed NUIGMech1.0 mechanism using the directed relation graph method assisted by sensitivity analysis and isomer lumping. The lumped mechanism shows good performance on ignition delay time under wide conditions. The study revealed that the temperature after the first-stage ignition is higher and a larger amount of fuel is consumed at lower initial temperatures. The temperature at the first-stage ignition is relatively insensitive to the initial temperature. Further sensitivity analysis and reaction path analysis carried out based on the lumped mechanism show that the decomposition of RO₂ to produce alkene and HO₂is the most important reaction to inhibit the first-stage ignitions. The chain branching explosion closely related to the first-stage ignition will be terminated when the rate constant for the RO₂ decomposition is larger than that of the isomerization of RO₂ to produce QOOH. The NTC behavior as well as other characteristics of the first-stage ignition can be rationalized from the competition between these two reactions.