The SURF model and the curvature effect for PBX 9502

SURF is a high explosive burn model based on the ignition & growth concept of hot-spot reaction. For the TATB based explosive PBX 9502, the model has been calibrated to shock-to-detonation transition experiments. To apply the SURF model for propagating detonation waves, the rate has to be extended to a higher pressure regime than is sampled by shock initiation experiments. The experimentally measured curvature effect – detonation speed as a function of front curvature or D _n(κ) – provides the appropriate data for calibrating the propagation regime. The calibration to the curvature effect is based on the ODEs for the reaction zone profile of a detonation wave in conjunction with a shooting algorithm to determine the rate model parameters, for a given κ, needed to obtain a specified detonation speed. A complication for calibrating PBX 9502 rate models arises from the kink in the experimentally measured D _n(κ) curve. This results from the fast and slow reactions that TATB exhibits. To account for this, we use an extension of the SURF model that utilises a sequence of two reactions. The first, with a fast rate, is due to molecular decomposition and is described by the original SURF formulation. The second, with a slow rate, is due to carbon clustering and is used to contribute additional energy from the formation of carbon bonds. The wave profile equations are generalised to the SURF-plus model. Model parameters are then determined for the propagation regime to fit the curvature effect data. The extended model is applicable to both the shock initiation regime and the propagating detonation wave regime.     

Nonequilibrium Zeldovich-von Neumann-Doring theory and reactive flow modeling of detonation

This paper discusses the Nonequilibrium Zeldovich-von Neumann-Doring (NEZND) theory of self-sustaining detonation waves and the Ignition and Growth reactive flow model of shock initiation and detonation wave propagation in solid explosives. The NEZND theory identified the nonequilibrium excitation processes that precede and follow the exothermic decomposition of a large high explosive molecule into several small reaction product molecules. The thermal energy deposited by the leading shock wave must be distributed to the vibrational modes of the explosive molecule before chemical reactions can occur. The induction time for the onset of the initial endothermic reactions can be calculated using high pressure-high temperature transition state theory. Since the chemical energy is released well behind the leading shock front of a detonation wave, a physical mechanism is required for this chemical energy to reinforce the leading shock front and maintain its overall constant velocity. This mechanism is the amplification of pressure wavelets in the reaction zone by the process of de-excitation of the initially highly vibrationally excited reaction product molecules. This process leads to the development of the three-dimensional structure of detonation waves observed for all explosives. For practical predictions of shock initiation and detonation in hydrodynamic codes, phenomenological reactive flow models have been developed. The Ignition and Growth reactive flow model of shock initiation and detonation in solid explosives has been very successful in describing the overall flow measured by embedded gauges and laser interferometry. This reactive flow model uses pressure and compression dependent reaction rates, because time-resolved experimental temperature data is not yet available. Since all chemical reaction rates are ultimately controlled by temperature, the next generation of reactive flow models will use temperature dependent reaction rates. Progress on a statistical hot spot ignition and growth reactive flow model with multistep Arrhenius chemical reaction pathways is discussed. The text was submitted by the authors in English.     

弹粘塑性双球壳塌缩热点反应模型

 基于Kim的弹粘塑性单球壳塌缩模型,考虑PBX炸药中的粘结剂效应,假设炸药和粘结剂均为弹粘塑性材料,建立了弹粘塑性双球壳塌缩热点反应模型,给出了炸药球壳在冲击压力作用下的速度、应变、温度和化学反应速率的时空分布,以及新的热点反应速率理论表达式。把新的热点反应项与Kim的低压下慢反应项和张震宇提出的高压反应速率方程相结合,得到了新的冲击起爆三项式细观反应速率模型。把该模型加入DYNA2D中,模拟了PBX-9501炸药的一维冲击起爆过程,结果表明：该模型除了可以解释炸药颗粒度和孔隙度的影响外,还可以较好地描述粘结剂强度和含量对PBX炸药冲击起爆感度的影响。     

利用电磁法研究HMX与TATB混合钝感炸药的冲击起爆特性

为研究含有少量奥克托金(HMX)且以三氨基三硝基苯(TATB)为基的高能钝感炸药PBX-3的冲击起爆反应增长规律,采用火炮驱动蓝宝石飞片的方法和铝基组合式电磁粒子速度计技术进行了一维平面冲击实验。通过实验测量撞击表面及内部不同深度处的冲击波后粒子速度,得到PBX-3炸药的Hugoniot关系。根据冲击波示踪器所测数据绘制了炸药到爆轰的时间-距离(x-t)图,获得了反映炸药冲击起爆性能的Pop关系。将入射压力为12.964 GPa时达到爆轰的6条速度曲线修整成相同零点,通过读取6条曲线的分离点即反应区末端的C-J点,计算出化学反应区时间和宽度。     

Experimental study and modeling of shock tube ignition delay times for hydrogen-oxygen-argon mixtures at low temperatures

Recent literature has indicated that experimental shock tube ignition delay times for hydrogen combustion at low-temperature conditions may deviate significantly from those predicted by current detailed kinetic models. The source of this difference is uncertain. In the current study, the effects of shock tube facility-dependent gasdynamics and localized pre-ignition energy release are explored by measuring and simulating hydrogen-oxygen ignition delay times. Shock tube hydrogen-oxygen ignition delay time data were taken behind reflected shock waves at temperatures between 908 to 1118 K and pressures between 3.0 and 3.7 atm for two test mixtures: 4% H₂, 2% O₂, balance Ar, and 15% H₂, 18% O₂, balance Ar. The experimental ignition delay times at temperatures below 980 K are found to be shorter than those predicted by current mechanisms when the normal idealized constant volume (V) and internal energy (E) assumptions are employed. However, if non-ideal effects associated with facility performance and energy release are included in the modeling (using CHEMSHOCK, a new model which couples the experimental pressure trace with the constant V, E assumptions), the predicted ignition times more closely follow the experimental data. Applying the new CHEMSHOCK model to current experimental data allows refinement of the reaction rate for H + O₂ + Ar ↔ HO₂ + Ar, a key reaction in determining the hydrogen-oxygen ignition delay time in the low-temperature region.     

金属隔层和空气间隙对钝感炸药冲击起爆的影响

为了确定空气间隙和金属隔层对冲击起爆的影响,采用火炮加载蓝宝石飞片冲击起爆Φ50 mm×30 mm的A型炸药,产生的冲击波通过空气间隙和金属隔层起爆Φ50 mm的台阶型B型炸药。在B型炸药的后界面粘贴镀膜氟化锂(LiF)窗口,使用光子多普勒测速仪(PDV)测量金属和B型炸药的后界面速度,进而计算得到金属和B型炸药的冲击波透射压力,再利用阻抗匹配计算得到金属和B型炸药的入射压力。结果表明:传爆药和金属隔层间的空气间隙使冲击压缩过程转变为准等熵压缩和冲击压缩两个过程,同时使冲击波的幅值减小;确定了金属隔层厚度为5 mm时冲击波压力的衰减范围;当使用A型炸药作为传爆药,空气间隙为0.3 mm,金属隔层厚度为5 mm时,B型炸药在7~10 mm之间开始反应。     

激光聚变冲击波点火的热斑形成机制

通过对冲击波点火内爆过程的数值模拟分析点火热斑压缩及形成机制。分析了传统中心点火的内爆过程,热斑主要经历冲击波压缩和惯性压缩过程,点火主要通过惯性压缩来实现。并仔细分析了冲击波点火的内爆压缩过程,从内爆角度来看冲击波点火并不是压缩和点火分开的两步过程,点火冲击波实际参与压缩过程,点火冲击波对热斑的直接影响很有限,热斑仍然主要通过壳层的惯性压缩实现点火。利用惯性压缩的定标关系及冲击波碰撞对壳层影响规律分析了热斑增压的物理机制,冲击波点火是通过点火冲击波与回冲击波的碰撞来提高壳层的密度,从而实现热斑压力的提升。     

Acetaldehyde oxidation at elevated pressure

A detailed chemical kinetic model for oxidation of CH₃CHO at intermediate to high temperature and elevated pressure has been developed and evaluated by comparing predictions to novel high-pressure flow reactor experiments as well as shock tube ignition delay measurements and jet-stirred reactor data from literature. The flow reactor experiments were conducted with a slightly lean CH₃CHO/O₂ mixture highly diluted in N₂ at 600–900 K and pressures of 25 and 100 bar. At the highest pressure, the oxidation of CH₃CHO was in the NTC regime, controlled to a large extent by the thermal stability and reactions of peroxide species such as HO₂, CH₃OO, and CH₃C(O)OO. Model predictions were generally in good agreement with the experimental data, even though the predicted temperature for onset of reaction was overpredicted at 100 bar. This discrepancy was attributed mainly to uncertainties in the CH₃C(O)OO reaction subset. Predictions of ignition delays in shock tubes and species profiles in JSR experiments were also satisfactory. At temperatures above the NTC regime, acetaldehyde ignition and oxidation is affected mainly by the competition between dissociation of CH₃CHO and reaction with the radical pool, and by reactions in the methane subset.     

Ignition limit and shock-to-detonation transition mode of n-heptane/air mixture in high-speed wedge flows

In this work, oblique detonation of n-heptane/air mixture in high-speed wedge flows is simulated by solving the reactive Euler equations with a two-dimensional (2D) configuration. This is a first attempt to model complicated hydrocarbon fuel oblique detonation waves (ODWs) with a detailed chemistry (44 species and 112 reactions). Effects of freestream equivalence ratios and velocities are considered, and the abrupt and smooth transition from oblique shock to detonation are predicted. Ignition limit, ODW characteristics, and predictability of the transition mode are discussed. Firstly, homogeneous constant-volume ignition calculations are performed for both fuel-lean and stoichiometric mixtures. The results show that the ignition delay generally increases with the wedge angle. However, a negative wedge angle dependence is observed, due to the negative temperature coefficient effects. The wedge angle range for successful ignition of n-heptane/air mixtures decreases when the wedge length is reduced. From two-dimensional simulations of stationary ODWs, the initiation length generally decreases with the freestream equivalence ratio, but the transition length exhibits weakly non-monotonic dependence. Smooth ODW typically occurs for lean conditions (equivalence ratio < 0.4). The interactions between shock/compression waves and chemical reaction inside the induction zone are also studied with the chemical explosive mode analysis. Moreover, the predictability of the shock-to-detonation transition mode is explored through quantifying the relation between ignition delay and chemical excitation time. It is demonstrated that the ignition delay (the elapsed time of the heat release rate, HRR, reaches the maximum) increases, but the excitation time (the time duration from the instant of 5% maximum HRR to that of the maximum) decreases with the freestream equivalence ratio for the three studied oncoming flow velocities. Smaller excitation time corresponds to stronger pressure waves from the ignition location behind the oblique shock. When the ratio of excitation time to ignition delay is high (e.g., > 0.5 for n-C₇H₁₆, > 0.3 for C₂H₂ and > 0.2 for H₂, based on the existing data compilation in this work), smooth transition is more likely to occur.     

冲击作用下HMX晶体孔洞塌缩热点生成机制的细观数值模拟

热点的形成、点火以及成长过程是理解非均匀炸药冲击起爆的关键.采用离散元法,对冲击作用下含孔洞的HMX晶体进行了细观数值模拟.计算结果表明:在较低冲击作用下,孔洞边缘发生了较大的剪切变形,粘塑性功形成热点;而在较高冲击作用下,孔洞塌缩产生射流,汇聚流动,冲击下游炸药形成热点,并获得了孔洞塌缩和热点生成演化的细观过程.     

Application of an aerosol shock tube to the measurement of diesel ignition delay times

Shock tube ignition delay times were measured for DF-2 diesel/21% O₂/argon mixtures at pressures from 2.3 to 8.0 atm, equivalence ratios from 0.3 to 1.35, and temperatures from 900 to 1300 K using a new experimental flow facility, an aerosol shock tube. The aerosol shock tube combines conventional shock tube methodology with aerosol loading of fuel-oxidizer mixtures. Significant efforts have been made to ensure that the aerosol mixtures were spatially uniform, that the incident shock wave was well-behaved, and that the post-shock conditions and mixture fractions were accurately determined. The nebulizer-generated, narrow, micron-sized aerosol size distribution permitted rapid evaporation of the fuel mixture and enabled separation of the diesel fuel evaporation and diffusion processes that occurred behind the incident shock wave from the chemical ignition processes that occurred behind the higher temperature and pressure reflected shock wave. This rapid evaporation technique enables the study of a wide range of low-vapor-pressure practical fuels and fuel surrogates without the complication of fuel cracking that can occur with heated experimental facilities. These diesel ignition delay measurements extend the temperature and pressure range of earlier flow reactor studies, provide evidence for NTC behavior in diesel fuel ignition delay times at lower temperatures, and provide an accurate data base for the development and comparison of kinetic mechanisms for diesel fuel and surrogate mixtures. Representative comparisons with several single-component diesel surrogate models are also given.     

JB-9001钝感炸药冲击Hugoniot关系测试

 利用“压力对比法”实验技术，通过锰铜压力计测试待测炸药样品和LY12铝样品在LY12铝飞片的同时撞击下的界面压力p_exp和p_Al，从冲击波关系式和正交回归直线拟合分析，确定了JB-9001钝感炸药的冲击Hugoniot关系。     

Experimental and kinetic modeling of the ignition delays of cyclohexane,cyclohexene, and cyclohexadienes: Effect of unsaturation

Cyclic and aromatic hydrocarbons are important components of usual commercial fuels, with C₆-rings being among the most abundant cyclic structures. The combustion chemistry of C₆-rings involves different levels of unsaturation, either as initial fuels (aromatics, naphtenes, …) or as intermediates formed during their combustion. In this work the ignition delays of cyclohexane, cyclohexene, 1,3-cyclohexadiene and 1,4-cyclohexadiene are systematically studied using experiments and kinetic modeling. Shock tube experiments were performed at high-temperature (above 1200 K) and for mean pressures of 6 atm. A detailed chemical kinetic model was developed that includes the combustion chemistry of the four cyclo-C₆ fuels. Electronic structure calculations were performed at the CCSD(T)/CBS//B2PLYP-D3 level of theory on the pericyclic reactions of the unsaturated fuels. Pressure-dependent rate coefficients were computed by solving the master equation, and included in the mechanism. The model was validated against the new ignition data and against data of the literature. It was able to reproduce the experimental ranking of reactivity: cyclohexene > 14-CHD > cyclohexane > benzene ≈13-CHD. Kinetic analyses were performed to explain this difference of reactivity. It is shown that pericyclic reactions play a major role in the initial decomposition of the unsaturated fuels.     

A study of detonation diffraction and failure for a model of compressible two-phase reactive flow

A two-phase model of heterogeneous explosives, with a reaction rate that is proportional to the gas-phase pressure excess above an ignition threshold, is examined computationally. The numerical approach, a variant of Godunov's method designed to accommodate nonconservative terms in the hyperbolic model, extends previous work of the authors to two-dimensional configurations. The focus is on the behavior of an established detonation as it rounds a 90° corner and undergoes diffraction. The dependence of the post-diffraction conduct on the reaction rate is explored by varying the reaction-rate prefactor and the ignition threshold. The aim is to determine whether the model, as postulated, can capture dead zones, which are pockets of unreacted or partially reacted explosive observed in the vicinity of the corner in diffraction experiments. Results of this study are compared with those of a similar investigation on the one-phase ignition-and-growth model.     

JP-10点火延时的激波管研究

在预加热激波管上测定了JP-10的点火延时时间．采用高精度真空仪直接测定注入激波管中JP-10蒸气压力，获得了JP-10气相浓度，解决了高碳数碳氢燃料点火延时激波管实验时管壁吸附影响燃料气相浓度确定的困难．采用压力传感器、单色仪和光电倍增管记录得到了完整的点火过程引起的压力变化和OH或CH自由基发射强度变化．自由基发射信号作为诊断点火发生的手段．当实验压力为151?556 kPa，温度为1000?2120 K，JP-10摩尔百分比为0.1%?0.55%，化学当量比为0.25、0.5、1.0、2.0时，获得了点火延时时间与实验温度、JP-10浓度、O2浓度的依赖关系，结果还表明，高温区和低温区呈现出不同的依赖关系．     

PBX-9502炸药爆轰反应速率模型研究

利用高能炸药爆轰反应的拉格朗日分析方法,得到了一个形式简单的PBX-9502炸药的爆轰反应速率方程。运用该速率方程,计算了PBX-9502炸药爆轰波反应区的纵向结构,并与三项式点火增长模型的计算结果及实验结果进行比较。结果表明:该爆轰反应速率方程能很好地模拟PBX-9502炸药爆轰波反应区的纵向结构。     

Synthesis of CsCl-type single-phase RuSi under shock compression

Shock recovery experiments were performed on ruthenium–silicon powder mixtures by a flyer plate impact technique. The flyer velocities were in the range of 0.46–2.73 km/s, and the incident shock pressures were calculated to be ～2.9–～40.4 GPa by the impedance matching method. The recovered samples were characterized by X-ray diffraction and scanning electron microscopy. Results indicate that shock could induce a reaction between ruthenium and silicon. The shock pressure was found to affect reaction kinetics and microstructure of the recovered sample significantly. The dynamic reaction has a threshold pressure, and the samples loaded above threshold pressure almost completely reacted to a single-phase intermetallic compound of CsCl-type RuSi. These results indicate that shock compression could be an effective way to synthesize RuSi.     

TNT/RDX（40/60）炸药球水中爆炸波研究

 利用锰铜计、PVDF计和电气石计分别测量了TNT/RDX（40/60）炸药球水中爆炸波峰压,得到了在1≤R/R₀≤400比例距离范围内的峰压衰减规律。利用电气石计得到的爆炸远区压力时程和气泡脉动周期资料证实了水中爆炸测试法评估炸药能量的可行性。     

Autoignition of ethylene in shock waves

The delay time of ignition of various C₂H₄-O₂-Ar mixtures behind reflected shock waves were measured at temperatures of 1090–1520 K and a pressure of 0.65 ± 0.05 MPa. A kinetic scheme of the ignition of ethylene based on the known rate constants of the key elementary reactions was developed. The scheme satisfactorily describes our own and published data on the ignition of ethylene in shock waves over wide ranges of temperature (1100–2400 K), pressure (0.006–0.64 MPa) and ethylene (0.1–17.4 vol %) and oxygen (0.6–20.7 vol %) concentrations.