铝粉-空气混合物爆燃转爆轰过程及爆轰波结构

 在长为32.4 m、内径为0.199 m的大型长直水平管道中,对铝粉-空气两相流的燃烧转爆轰（DDT）过程及爆轰波结构进行了实验研究。对铝粉-空气混合物弱点火条件下DDT过程不同阶段的特征进行了分析,实验结果显示混合物经历了缓慢反应压缩阶段、压缩波加速冲击波形成阶段、冲击反应过渡阶段、冲击反应向过压爆轰过渡阶段和爆轰阶段,得到了混合物各阶段的DDT参数,由此进一步分析了DDT浓度的上、下限。在1.4 m爆轰测试段的4个截面的环向上各均匀安装8个传感器,对爆轰波结果进行测试,并对铝粉-空气混合物爆轰波的单头结构进行了分析。     

凝聚炸药中超压爆轰的实验研究

 采用飞片碰撞技术，在TNT/RDX（40/60）炸药中获得了2.5倍于正常爆轰的最大超压值，得到了超压爆轰下爆轰产物物态方程p=Aρ^{k+A₁(p-p_J)}（p－爆压，单位GPa，ρ－密度，单位kg/m³，A=ρ_J/ρ^k_J，p_J=27.06 GPa，ρ_J=2.3×10³ kg/m³，k=2.77，A₁=2.7×10^-3 GPa^-1，下表J代表正常爆轰状态）。该方程还可以较好地描述超压爆轰产物的二次冲击状态。     

瞬态光谱法确定环氧丙烷DDT过程中起主导作用的基团

解决了燃料爆燃转爆轰(DDT)过程初始阶段弱辐射瞬态光谱测试问题、反应中间产物辐射相对强度定标问题和瞬态光谱测试系统同步控制问题后,从爆炸激波管的6个不同侧窗,拍摄了环氧丙烷DDT过程不同距离处的曝光时间为2～8 μs、分辨率达到0.2 nm的瞬态发射光谱。对所测光谱进行相对强度定标后,得到了主要反应中间产物光辐射强度随燃烧波阵面传播距离的变化曲线, 此曲线反映出DDT过程中反应中间产物的发展过程和其相应的浓度变化。结果显示,在爆燃阶段,燃烧气体的化学反应速率平缓增加,反应中间产物浓度逐渐增大;但在爆燃转爆轰的瞬间,反应急剧增快,反应中间产物的浓度突跃式地成倍增大。其中CO分子和CHO,OH自由基的浓度增幅显著大于其他反应产物,表明这几个基团是环氧丙烷爆燃转爆轰过程中起主导作用的重要基团。     

动载荷下金属板表面的微物质喷射

 用石英晶体传感器技术，测量了冲击波作用下铝合金（Ly-12）和纯铅样品自由表面的微物质喷射量。在冲击压力为32 GPa时，测得光洁度为3.2、0.4、0.1 μm的铝合金的微物质喷射量分别为1.53～3.28 g/m²，0.2～0.3 g/m²和0.053～0.096 g/m²，对光洁度为3.2 μm的纯铅样品，在压力为13 GPa和47 GPa时，微物质喷射量分别微26.4～42.4 g/m²和183～328 g/m²。在最高冲击压力约为20 GPa时，做了多次冲击下的微物质喷射量测量，发现比单次冲击加载下的喷射量有很大的减少。结果表明，微物质喷射量与自由表面的加工条件、局部熔化和加载方式等因素有关。     

气相DDT中过爆轰现象产生条件的实验研究

针对目前国际上关于气相过爆轰产生条件的3种不同观点,利用压力传感器,实验研究了氢氧混合物的爆燃转爆轰(DDT)全过程。获得了比较完整的、能反映气相DDT从爆燃成长为过爆轰再衰减为稳定爆轰的全过程压力变化曲线。分析实验结果表明,氢氧混合物的DDT过程中,过爆轰的产生需要一定条件;在初始压力一定的情况下,氢氧混合物DDT过程的转变时间或距离随氢气浓度的增加,先减小后增大,过爆轰的压力峰值约为稳定爆轰压力的1.5～2倍。     

SU(2)×U(1)×S3模型及类K0-K0系统的混合和CP破坏效应

本文内容包括:(ⅰ)进一步给出SU(2)×U(1)×S₃模型的结果S₂≈S₃≈(m_s²)/(m_b²);sin δ≤(m_um_d)/(m_cm_s),并预言b夸克的主要衰变道是b→u+W,b夸克的寿命可能长到10^-9秒.(ⅱ)给出类K⁰-K⁰系统混合时的精确表达式ρ=错号事例数/对号事例数=(1/2)(|p/q|²+|q/p|²)([Γ²+(Δm)²]²-(γ1γ2)²)/([Γ²+(Δm)²]²+(γ1γ2)²);并给出CP破坏的精确表达式:A=(1-ρ')/(1+ρ')=(I_M12Γ₁₂^*)/(|M₁₂|²+1/4|Γ₁₂|²),这里ρ′=(负电错号事例数)/(正电错号事例数)。     

氢气/甲烷-空气爆轰波在含环形障碍物圆管内传播的试验研究

在内径48mm、长度5 800mm的含环形障碍物圆管内,进行了氢气-空气及氢气-甲烷-空气的爆轰波传播试验研究,确定了爆燃转爆轰(Deflagration-to-Detonation Transition,DDT)极限。环形障碍物阻塞比为0.56,间距分为两种,即S=D和S=2D,其中S为障碍物间距,D为管道内径。火焰的速度由安装在管道壁面上的光电二极管采集得到。试验测量得到的火焰为准爆轰或阻塞火焰。在S=2D情况下得到的火焰速度均比S=D情况下的火焰速度高,并且靠近DDT极限时速度波动更明显,表明在间距较大的情况下爆轰的重起爆循环周期更长,类似于"弛振爆轰"。对于氢气-空气,障碍物间距为D时在DDT极限处有d/λ1(富氧条件下d/λ=1.6,贫氧条件下d/λ=1.4),间距为2D时更容易形成爆轰的重起爆,在DDT极限处与准则d/λ≈1一致;对于氢气-甲烷-空气,甲烷的添加使爆轰更不稳定,对于两种间距的障碍物得到的DDT极限均有d/λ≈1(d和λ分别为障碍物内径和爆轰胞格尺寸)。说明障碍物间距对爆轰波传播有显著的影响,即间距的增大更有利于爆轰波的传播。为形成准爆轰,障碍物内径必须至少可以容纳一个爆轰胞格,同时障碍物间距足够大从而引起爆轰的重起爆。     

拐角空间中悬浮铝粉尘爆轰后效的三维数值模拟

建立三维的铝粉-空气两相爆轰计算模型，采用时-空守恒元解元（CE/SE）方法求解，并开发了悬浮铝粉尘爆轰的三维数值模拟程序.基于消息传递接口（MPI）技术实现了程序的并行化设计.通过对激波管问题以及爆轰管中铝粉-空气两相爆轰实验的模拟验证程序的可靠性.对拐角空间中左侧浓度为368 g·m^-3的铝粉-空气混合物两相爆轰及其在拐角空间右侧和下方空气域内形成的冲击波和温压效应开展数值模拟，获得复杂空间内爆轰波或冲击波的传播、反射以及绕射过程.结果表明：两相爆轰在离铝粉尘区域2 m远的空气域内产生的后效冲击波能达到2.66 MPa的固壁反射压力，火球燃烧范围会超出初始铝粉尘区域约0.8 m，并且造成初始铝粉尘区域附近1.5 m范围内空气的温度高达1 600 K.模拟程序可用于铝粉尘爆轰的后效研究，对工业安全及其防护具有指导意义.     

对带电轻子质量公式的一些猜测

本文建议轻子电磁自能通过（（δm）/m）=（1/（2π））n^-b 与量子数 n 联系起来,其中 b 为待定常数.并建议动量截断值 M 与引力常数 k 和精细结构常数α的联系为 M=（?）.得到了带电轻子质量公式（?）.利用 e^-和μ^-质量的实验值和α值作输入,给出计算值 k=（6.67231±0.00026）×10^-8 cm³g^-lsec^-2和m_τ=（1782.306±0.078）MeV,与观察值 k=（6.6720±0.0041）×10^-8cm³ g^-1sec^-2和 m_τ=(1782_-4⁺³)MeV 很好符合.公式预言第四个带电轻子质量应为 m=（11725.47±0.51）MeV 可以在最近的实验中检验。本文还对所建议的质量公式和结果进行了讨论.     

掺铒碲钨酸盐玻璃光谱性质的研究

合成了不同浓度Er³⁺掺杂的TeO₂-WO₃-Li₂O体系玻璃（TW glasses）,详细研究了掺杂浓度对这种碲钨酸盐玻璃光学特性的影响。计算了Judd Ofelt(J-O)强度参数,研究了掺杂浓度对15 μm发射带宽的影响,及不同掺杂浓度下Er³⁺的⁴I_11/2-⁴I_13/2和⁴I_13/2-⁴I_15/2无辐射跃迁过程。实验得到了在TW 玻璃中Er³⁺的⁴I_13/2-⁴I_15/2跃迁的浓度猝灭速率约为跃迁的浓度猝灭速率约为0.8×10^-18cm³·s^-1,这对寻求Er³⁺在碲钨酸盐玻璃中的合理掺杂浓度有一定的参考意义,这对寻求Er³⁺在碲钨酸盐玻璃中的合理掺杂浓度有一定的参考意义。实验发现Er³⁺的⁴I_11/2-⁴I_13/2无辐射弛豫速率在这种玻璃体系中约是不含WO₃的碲酸盐玻璃中的2倍,说明含WO₃的掺铒碲钨酸盐玻璃更有利于在980 nm激光泵浦下实现15 μm光放大。     

Detonation simulations in supersonic flow under circumstances of injection and mixing

The unsteady, reactive Navier-Stokes equations with a detailed chemical mechanism of 11 species and 27 steps were employed to simulate the mixing, flame acceleration and deflagration-to-detonation transition (DDT) triggered by transverse jet obstacles. Results show that multiple transverse jet obstacles ejecting into the chamber can be used to activate DDT. But the occurrence of DDT is tremendously difficult in a non-uniform supersonic mixture so that it required several groups of transverse jets with increasing stagnation pressure. The jets introduce flow turbulence and produce oblique and bow shock waves even in an inhomogeneous supersonic mixture. The DDT is enhanced by multiple explosion points that are generated by the intense shock wave focusing of the leading flame front. It is found that the partial detonation front decouples into shock and flame, which is mainly caused by the fuel deficiency, nevertheless the decoupled shock wave is strong enough to reignite the mixture to detonation conditions. The resulting transverse wave leads to further mixing and burning of the downstream non-equilibrium chemical reaction, resulting in a high combustion temperature and intense flow instabilities. Additionally, the longitudinal and transverse gradients of the non-uniform supersonic mixture induce highly dynamic behaviors with sudden propagation speed increase and detonation front instabilities.     

Deflagration-to-detonation transition in air-binary fuel mixtures in an obstacle-laden channel

The results of studying deflagration-to-detonation transition (DDT) in hydrogen-methane (propane)-air in a detonation tube with uniformly spaced annular obstacles are presented. The effect of the scaling factor on the DDT was identified. The boundary between fast deflagration and detonation regimes was calculated using a criterion based on a comparison of the gasdynamic and chemical characteristic times for the ignition of the mixture behind the shock wave reflected from an obstacle.     

HMX炸药燃烧转爆轰数值模拟

以两相流模型为基础,气相产物状态方程采用基于统计物理的类CHEQ的计算结果,建立了HMX炸药的燃烧转爆轰数学模型。采用CE/SE方法模拟了颗粒度为125μm的HMX炸药的燃烧转爆轰过程,得到了爆轰参数及流场变化规律。模拟了装填密度对HMX炸药燃烧转爆轰的影响,并与实验进行了对比。数值模拟结果表明,在相同的点火条件下,爆轰成长距离在一定范围内随装填密度呈"U"形变化。     

An experimental investigation of the onset of detonation

An experimental configuration is devised in the present investigation whereby the condition at the final phase of the deflagration to detonation transition (DDT) process can be generated reproducibly by reflecting a CJ detonation from a perforated plate. The detonation products are transmitted downstream through the plate, generating a turbulent reaction front that mixes with the unburned mixture and that drives a precursor shock ahead of it at a strength of about M = 3. The gasdynamic condition that is generated downstream of the perforated plate closely corresponds to that just prior to the onset of detonation in the DDT process. The turbulence parameters can be controlled by varying the geometry of the perforated plate; thus, the condition leading to the onset of detonation can be experimentally investigated. A one-dimensional theoretical analysis of the steady wave processes was first performed, and the experimental results show good agreement, indicating that the present experimental condition can be theoretically described. Two different detonation tube geometries (one with a square cross-section of 300 mm by 300 mm and the other with a circular cross-section of 150 mm) are used to demonstrate the independence of the tube diameter at the critical condition for DDT. Perforated plates with different hole diameters (d = 8, 15, and 25 mm) were tested, and the hole spacing to hole diameter ratio was maintained at 0.5. Different hydrogen–air mixtures were tested at normal temperature and pressure. For the plate with 8 mm holes, the onset of detonation is never observed. For the plate with 15 mm holes, successful initiation of a detonation is achieved for 0.8 < < 1.75 in both detonation tubes. For the plate with 25 mm holes, detonation initiation is observed for 0.7 < < 2.1 in the square detonation tube and for 0.8 < < 1.6 in the smaller circular detonation tube.     

Effect of actuating frequency on plasma assisted detonation initiation

Aiming at studying the influence of actuating frequency on plasma assisted detonation initiation by alternating current dielectric barrier discharge, a loosely coupled method is used to simulate the detonation initiation process of a hydrogenoxygen mixture in a detonation tube at different actuating frequencies. Both the discharge products and the detonation forming process which is assisted by the plasma are analyzed. It is found that the patterns of the temporal and spatial distributions of discharge products in one cycle are not changed by the actuating frequency. However, the concentration of every species decreases as the actuating frequency rises, and atom O is the most sensitive to this variation, which is related to the decrease of discharge power. With respect to the reaction flow of the detonation tube, the deflagration-todetonation transition(DDT) time and distance both increase as the actuating frequency rises, but the degree of effect on DDT development during flow field evolution is erratic. Generally, the actuating frequency affects none of the amplitude value of the pressure, temperature, species concentration of the flow field, and the combustion degree within the reaction zone.     

Reaction propagation modes in millimeter-scale tubes for ethylene/oxygen mixtures

Effects of tube diameter and equivalence ratio on reaction front propagations of ethylene/oxygen mixtures in capillary tubes were experimentally analyzed using high speed cinematography. The inner diameters of the tubes investigated were 0.5, 1, 2 and 3 mm. The flame was ignited at the center of the 1.5 m long smooth tube under ambient pressure and temperature before propagated towards the exits in the opposite directions. A total of five reaction propagation scenarios, including deflagration-to-detonation transition followed by steady detonation wave transmission (DDT/C–J detonation), oscillating flame, steady deflagration, galloping detonation and quenching flame, were identified. DDT/C–J detonation mode was observed for all tubes for equivalence ratios in the vicinity of stoichiometry. The velocity for the steady detonation wave propagation was approximately Chapman–Jouguet velocity for 1, 2, and 3 mm I.D. tubes; however, a velocity deficit of 5% was found for the case in 0.5 mm I.D. tube. For leaner mixtures, an oscillating flame mode was found for tubes with diameters of 1 to 3 mm, and the reaction front travelled in a steady deflagrative flame mode with velocities around 2–3 m/s when the mixture equivalence ratio becomes even leaner. Galloping detonation wave propagation was the dominant mode for the fuel lean regime in the 0.5 mm I.D. tube. For rich mixtures beyond the detonation limits, a fast flame followed by flame quenching was observed.     

On the mechanism of the deflagration-to-detonation transition in a hydrogen-oxygen mixture

The flame acceleration and the physical mechanism underlying the deflagration-to-detonation transition (DDT) have been studied experimentally, theoretically, and using a two-dimensional gasdynamic model for a hydrogen-oxygen gas mixture by taking into account the chain chemical reaction kinetics for eight components. A flame accelerating in a tube is shown to generate shock waves that are formed directly at the flame front just before DDT occurred, producing a layer of compressed gas adjacent to the flame front. A mixture with a density higher than that of the initial gas enters the flame front, is heated, and enters into reaction. As a result, a high-amplitude pressure peak is formed at the flame front. An increase in pressure and density at the leading edge of the flame front accelerates the chemical reaction, causing amplification of the compression wave and an exponentially rapid growth of the pressure peak, which “drags” the flame behind. A high-amplitude compression wave produces a strong shock immediately ahead of the reaction zone, generating a detonation wave. The theory and numerical simulations of the flame acceleration and the new physical mechanism of DDT are in complete agreement with the experimentally observed flame acceleration, shock formation, and DDT in a hydrogen-oxygen gas mixture.     

A scaling analysis of the critical conditions for a deflagration-to-detonations transition

In this paper an intuitive criterion for the deflagration-to-detonations transition (DDT) by turbulent mixing was deduced. An analysis was first carried out to determine the critical conditions for detonation initiation within a reactive mixture, which is non-uniformly heated. It was demonstrated that the critical conditions depend on both the size and the characteristic heating time of the energy source. If the characteristic heating time is larger than a critical value, no detonation initiation can be expected, no matter how large the total energy of the heat source is. The critical parameters obtained were then applied to determine the critical conditions for detonation initiation via turbulent mixing. It was found that the DDT depends on both the mixing time and length scales. According to the Damkohler number, there are two regimes. (a) When the Damkohler number is smaller than unity, the critical integral length scale for DDT decreases as the inverse of the turbulent velocity. (b) When the Damkohler number is larger than unity, the critical integral length scale increases according to the cube of the turbulent velocity. These critical conditions were explained in a turbulent phase diagram of Borghi.(Some figures in this article appear in colour in the electronic version; see www.iop.org)