大型水平爆轰管中悬浮铝粉爆炸过程的实验研究

铝粉的燃烧与爆轰性能是粉尘爆炸领域研究的热点.利用长29.6m,内径199mm,配有40套喷粉扬尘系统的水平爆轰管,在40J电火花点火条件下,实现了悬浮铝粉-空气混和物火焰加速、爆燃、爆轰及其转捩过程,测得了爆炸波传播过程中的压力信号,并且观察到了爆轰波的稳定传播现象.实验结果表明,当铝粉浓度为300 g/m3时,在距离点火端10.15m(长径比L/D=51)处发生了DDT,测得的爆轰波传播过程中管内的最大爆速为1840m/s,最大峰值超压为10.5MPa.铝粉尘爆炸波在爆轰管内的传播过程可分为爆燃段、爆燃转爆轰(DDT)、爆轰增强以及稳态爆轰四个阶段.     

Propagation mechanism of dust detonations

This paper summarizes the studies on dust detonations at the Stosswellenlabor of RWTH Aachen since 1987. The onset and propagation mechanism of heterogeneous dust detonations are similar to those of marginal gas phase detonations. A self-sustained dust detonation has transverse wave structures that provide the coupling between shock and reaction. Large transition distances and transverse wave spacings require large sized tubes for the propagation of self-sustained dust detonations. The Hugoniot analysis of the Chapman-Jouguet detonation predicts equilibrium detonation states being in reasonable agreement with the self-sustained dust detonations observed. Shock matching calculations at the triple point adequately determine the wave structures of those stable dust detonations.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Propagation of near-limit gaseous detonations in small diameter tubes

In this study, detonation limits in very small diameter tubes are investigated to further the understanding of the near-limit detonation phenomenon. Three small diameter circular tubes of 1.8, 6.3, and 9.5 mm inner diameters, of 3 m length, were used to permit the near-limit detonations to be observed over long distances of 300 to 1500 tube diameters. Mixtures with high argon dilution (stable) and without dilution (unstable) are used for the experiments. For stable mixtures highly diluted with argon for which instabilities are not important and where failure is due to losses only, the limit obtained experimentally appears well to be in good agreement in comparison to that computed by the quasi-steady ZND theory with flow divergence or curvature term modeling the boundary layer effects. For unstable detonations it is suggested that suppression of the instabilities of the cellular detonation due to boundary conditions is responsible for the failure of the detonation wave. Different near-limit propagation regimes are also observed, including the spinning and galloping mode. Based on the present experimental results, an attempt is made to study an operational criterion for the propagation limits of stable and unstable detonations.     

Behavior of detonation waves at low pressures

With respect to stability of gaseous detonations, unsteady behavior of galloping detonations and re-initiation process of hydrogen-oxygen mixtures are studied using a detonation tube of 14 m in length and 45 mm i.d. The arrival of the shock wave and the reaction front is detected individually by a double probe combining of a pressure and an ion probe. The experimental results show that there are two different types of the re-initiation mechanism. One is essentially the same as that of deflagration to detonation transition in the sense that a shock wave generated by flame acceleration causes a local explosion. From calculated values of ignition delay behind the shock wave decoupled from the reaction front, the other is found to be closely related with spontaneous ignition. In this case, the fundamental propagation mode shows a spinning detonation. Received 10 March 1997 / Accepted 8 June 1997     

Deflagration to detonation transition fueled by dust layers

The roles which dust layers play in severe dust explosions were investigated in a 70 m long and 30 cm inside diameter horizontal Flame Acceleration Tube (FAT) with one end closed and the other end open to the atmosphere. A variety of dusts such as corn dust, cornstarch, Mira Gel starch, wheat dust, and wood flour were layered on the bottom half of the FAT. To initiate the combustion process, a detonation tube filled with a stoichiometric H₂/O₂ mixture at room temperature and 1 atm pressure was used to ignite a short presuspended dust cloud with a dust concentration of 500–600 g/m³. Combustion waves generated by this dust cloud travel toward the open end of the FAT and are continuously fueled by the dust/air mixtures. Flame propagation processes in the FAT were closely monitored by a variety of measuring instruments at different locations. The study demonstrates that stable quasi-detonation were reached in some runs, but self-sustained Chapman-Jouguet detonations were not observed possibly due to the limitation of the tube length. Attempts were made to determine the structure of dust detonations fueled by a dust layer. Preliminary evidence indicates that for Mira Gel starch the leading shock is essentially a triple shock configuration which involves a Mach stem and for wheat and wood dusts there possibly exists a multi-headed spin structure.     

Combustion tube studies of dust flame acceleration

A new pneumatic dispersion system for obtaining a good quality uniform dust suspension in a horizontal dust combustion tube was developed. The effect of three different dispersion techniques on self-sustained dust flame acceleration in such a combustion tube was examined. The importance of the dispersion quality in the test tube for maintaining a self-sustained dust flame acceleration was demonstrated. A combustion tube for studies of flame acceleration in fine aluminum dust-air mixture and its transition to detonation under industrial ignition conditions was constructed in the course of the present study. It consists mainly of an initiation section and a test section. The initiation section must be equipped in a well-developed dispersion system for creating a good dispersion condition in the test tube. The length of this section is 3 meters. The test tube requires only to distribute uniformly the dust over the bottom of the tube prior to the experiment. The aluminum dust spherical in shape with 6 μm in diameter was used for tests. Experimental results demonstrated that the increase in flame velocity is roughly linear through the entire length of the test tube. The highest flame propagation velocity in fine aluminum dust-air mixture approaches some 1200m/s at a distance of 4.8m from the ignition plane.     

铝粉湍流火焰诱导激波现象的实验研究

粉尘湍流火焰诱导激波问题是工业灾害研究中的重要课题．本文在自行设计的大型卧式燃烧管内，对铝粉火焰诱导激波现象进行了实验研究，测试了湍流火焰阵面前压缩波到激波的转捩过程，并将实验结果与数值模拟结果进行了比较．     

Detonation formation in H $_2$-O $_2$/He/Ar mixtures at elevated initial pressures

In this paper the formation of detonation in H-O/He/Ar mixtures at elevated initial pressures was investigated in an initiation tube for a detonation driver with an exploding wire as the ignition source. In most experiments the detonation wave was formed by a DDT process in which a reactive shock wave accelerates behind the leading shock wave and eventually leads to the onset of detonation. The onset position was found to be at the leading shock wave or behind it. Only in very sensitive mixtures at high initial pressure the direct initiation of detonation was observed. The influence of ignition energy, initial pressure and composition on the detonation induction distance was determined. The results show that the detonation induction distance increases with the decrease of ignition energy and initial pressure and with the increase of the mole fraction of helium or argon. With the same mole fraction, argon increases the induction distance more than helium. In the facility utilized the DDT upper and lower limits of hydrogen in H-O mixtures are in the ranges from 36 to 40 % and from 78 to 82 %, respectively, and the upper limits for helium and argon in stoichiometric H-O mixtures are 40 % and 36 %, respectively. High pressure peaks generated by the DDT process were measured, especially in mixtures near the DDT limits. Statistical results show that such peak pressures can be up to 6 times of the CJ-pressures. Received 1 March 2000 / Accepted 25 May 2000     

多障碍物通道中激波诱导气相爆轰的数值研究

应用数值模拟方法，研究了直通道中激波经过多块矩形障碍物时诱导 H2/O2混合气体起爆的物理机制. 研究表明：在前导激波强度不足以诱导波后气 体直接起爆的条件下，经过激波压缩的可燃气体也可能在远离激波的障碍物之间的凹槽部位 起爆；障碍物表面产生的压缩波、膨胀波和气流滑移面对可燃气体的起爆、爆轰波的形成和 传播过程有重要的影响；添加不同稀释比的氮气可以影响爆轰波后流场的温度分布；增加障 碍物的间距可以改变可燃气起爆位置.     

Three-dimensional cellular structure of detonations in suspensions of aluminium particles

Recently, we have used scarce available data on the detonation cell size in suspensions of aluminium particles in air and oxygen to adjust the kinetic parameters of our two-phase model of detonations in these mixtures. The calculated detonation cell width was derived by means of two-dimensional (2D) unsteady simulations using an assumption of cylindrical symmetry of the flow in the tube. However, in reality, the detonation cells are three-dimensional (3D). In this work, we have applied the same detonation model which is based on the continuous mechanics of two-phase flows, for 3D numerical simulations of cellular detonation structures in aluminium particle suspensions in oxygen. Reasonable agreement on the detonation cell width was obtained with the aforementioned 2D results. The range of tube diameters where detonations in $\text{ Al/O}_2$ mixture at a given particle size and concentration would propagate in the spinning mode has been estimated (these results make a complement to our previous analysis of spinning detonations in Al/air mixtures). Coupling these results with the dependencies of detonation cell size on the mean particle diameter is of great interest for the understanding of fundamental mechanisms of detonation propagation in solid particle suspensions in gas and can help to better guide the experimental studies of detonations in aluminium suspensions. It is shown that the part of detonation wave energy used for transverse kinetic energy of both gas and particles is quite small, which explains why the propagation velocity of spinning and multi-headed detonations reasonably agrees with the ideal CJ values.     

正向爆轰驱动高焓激波风洞的数值模拟

对充满氢氧可燃气体、带扩容腔的正向爆轰驱动的激波风洞进行了数值模拟。计算采用了欧拉方程,频散可控耗散差分格式（DCD）和改进的二阶段化学反应模型。在扩容腔附近采用二维轴对称计算模型,而在驱动段和被驱动段的直管道部分则采用一维计算模型。本文分析了爆轰波在管道中的传播、反射和绕射过程。计算结果表明扩容腔的尺寸对爆轰波的传播、反射、汇聚等起着决定性的作用;带扩容腔的正向爆轰驱动的激波风洞能够得到平稳的持续时间较长的气流,提高了实验的精确度和可重复性。     

Cellular detonations in bidispersed gas-particle mixtures

Formation of cellular detonation in bi-fractional stoichiometric mixtures of aluminum particles and oxygen is investigated numerically. The detonation cell size depends on the particle diameters and relative concentration of the fractions. Certain degeneration of cellular detonation is obtained when compared to the monodisperse mixtures. It is characterized by maximal pressure decrease, transverse wave relaxation and detonation front rectification. Complete degeneration of cellular detonations and stable propagation of a plane detonation front is found in some bi-fractional mixtures. The numerical results are confirmed by acoustic analysis of the detonation structures. This paper is based on work that was presented at the 21st International Colloquium on the Dynamics of Explosions and Reactive Systems, Poitiers, France, July 23–27, 2007.     

A high-speed photographic study of the transition from deflagration to detonation wave

Experiments were conducted to investigate the DDT process of the oxyhydrogen gas in the rectangular detonation tube of 3 m long. The repeated obstacle was installed near the ignition plug and the effects of the obstacle on the DDT process were investigated. The behaviour of the combustion and detonation wave were visualized utilizing Imacon high-speed camera with the aid of Schlieren optics. As a result, DDT process was visualized, i.e. (i) multiple shock waves were induced by the expanding combustion wave, because the combustion flame played a role as a piston and compressed the unburned gases. (ii) The acceleration of the combustion wave was occurred and the distance between the shock wave and the combustion flame became shorter. (iii) Eventually, the local explosion was occurred and cause overdriven detonation wave to propagate at the velocity of about 3 kms⁻¹. An abridged version of this paper was presented at the 15th Int. Colloquium on the Dynamics of Explosions and Reactive Systems at Boulder, Colorado, from July 30 to August 4, 1995     

Analysis of the shock structures in a regular detonation

Time-dependent two-dimensional numerical simulations have been used to investigate the detailed shock structures and patterns of energy release in the regions of the triple points and transverse waves in a planar detonation. As the system of shock triple points evolves between collisions, they trace a well shaped cellular pattern characteristic of detonations in argon-diluted, low-pressure mixtures of hydrogen and oxygen. In the region of the triple points, the shock structure evolves continuously from a single Mach structure to a double Mach structure and finally to a complex Mach structure characteristic of spinning detonations. Most of the energy released in the region of the triple points. The amount of energy release increases as the triple point comes closer to a collision with a wall or another triple point. Just before the collision, there is a large region of energy release that covers the length of the interacting transverse waves. The result is a rectangular high-energy region which boosts the propagation of the new detonation cell.     

Aluminum Particles–air Detonation at Elevated Pressures

The effect of initial pressure on aluminum particles–air detonation was experimentally investigated in a 13 m long, 80 mm diameter tube for 100 nm and 2 μm spherical particles. While the 100 nm Al–air detonation propagates at 1 atm initial pressure in the tube, transition to the 2 μm aluminum–air detonation occurs only when the initial pressure is increased to 2.5 atm. The detonation wave manifests itself in a spinning wave structure. An increase in initial pressure increases the detonation sensitivity and reduces the detonation transition distance. Global analysis suggests that the tube diameter for single-head spinning detonation or characteristic detonation cell size would be proportional to (d ₀: aluminum particle size, p ₀: initial pressure). Its application to the experimental data results in m ~ O(1) and n ~ O(1) for 1 to 2 μm aluminum–air detonation, thus indicating a strong dependence on initial pressure and gas-phase kinetics for the aluminum reaction mechanism in detonation. Hence, combustion models based on the fuel droplet diffusion theory may not be adequate in describing micrometric aluminum–air detonation initiation, transition and propagation. For 2 μm aluminum–air mixtures at 2 atm initial pressure and below, experiments show a transition to a “dust quasi-detonation” that propagates quasi-steadily with a shock velocity deficit nearly 40% with respect to the theoretical C–J detonation value. The dust quasi- detonation wave can propagate in a tube with a diameter less than 0.4–0.5 times the diameter required for a spinning detonation wave.     

两种不同气体中的高速爆燃波及其向爆轰的转变

对2C2H2 5O2及2C2H2 5O2 80%Ar两种可燃混合气体中的高速爆燃波及其向爆轰的转变过程进行实验研究.高速爆燃波由孔栅干涉爆轰波的方法直接生成,观测手段则以高速转鼓摄影获取孔栅近场流场x-t纹影图,以传感器追踪波面的后继发展.研究发现,两种气体中的爆燃波具有迥异的特性.前者燃烧波面在较低初压条件下为层流结构,而较高初压下为湍流结构,向爆轰转变点可以延伸至下游较长距离;后者在不同初压条件下燃烧波面无明显差异,爆轰的再次形成只能在孔栅下游近场内建立.两种气体中高速爆燃波的维持和爆轰转变过程均非纯粹激波压缩所致,湍流输运在其中起着必不可少的作用.分析显示,激波压缩效应对纯氧炔气体的高速爆燃和DDT贡献较小,湍流输运占主导地位;而氩气稀释气体较为稳定,缺乏自行衍生剧烈湍流燃烧的能力,因而激波压缩和外界扰动对其高速爆燃传播和爆轰转变起十分重要的作用.     

Wave dynamic processes in cellular detonation reflection from wedges

When the cell width of the incident detonation wave (IDW) is comparable to or larger than the Mach stem height, self-similarity will fail during IDW reflection from a wedge surface. In this paper, the detonation reflection from wedges is investigated for the wave dynamic processes occurring in the wave front, including transverse shock motion and detonation cell variations behind the Mach stem. A detailed reaction model is implemented to simulate two-dimensional cellular detonations in stoichiometric mixtures of H ₂/O ₂ diluted by Argon. The numerical results show that the transverse waves, which cross the triple point trajectory of Mach reflection, travel along the Mach stem and reflect back from the wedge surface, control the size of the cells in the region swept by the Mach stem. It is the energy carried by these transverse waves that sustains the triple-wave-collision with a higher frequency within the over-driven Mach stem. In some cases, local wave dynamic processes and wave structures play a dominant role in determining the pattern of cellular record, leading to the fact that the cellular patterns after the Mach stem exhibit some peculiar modes. The English text was polished by Yumming Chen.     

Experiments on spinning detonations with detailed analysis of the shock structure

Spinning detonations are characteristic of detonation limit phenomena in round tubes. In this work we study experimentally the structure of the transverse wave of single-headed spinning detonations. The flow field is experimentally analysed and an original approach enables us to calculate the overall shock structure. The calculations and experimental results indicate that the actual structure of the spinning detonation tries to match closely to the condition where the state parameters (pressure and temperature) reach their maximum values. This condition corresponds to a spinning head where the Mach stem is normal to the incoming flow and could be readily used as boundary condition by further investigators to determine the structure of spinning detonations. Received 1 August 1997/ Accepted 13 July 1998     

Diffraction and re-initiation of detonations behind a backward-facing step

Diffraction phenomena of gaseous detonation waves behind a backward-facing step in a tube are observed by using high-speed schlieren photography and soot-track records as well as by pressure measurements on the sidewall. Mixtures are stoichiometric oxyhydrogen and those diluted by argon at sub-atmospheric pressures. Three types of phenomena are observed, that is, continuous propagation of detonation, re-initiation after a temporal extinction of detonation and complete extinction of detonation. The continuous propagation means that the diffracted wave does not affect the main propagation although reflected shock waves from the bottom surface of the tube may affect it. The re-initiation occurs at a wall surface of the tube behind a reflected shock wave after the main detonation wave has been extinguished. Positions and conditions of the re-initiation are discussed. The complete extinction is defined as disappearance of detonation cells behind the step within a certain length of the tube. Cases exist where an ignition occurs after several reflections off the bottom and top surface of the tube.     

Evolution of detonation propagation through an annular gap into a combustion chamber

Some results of theoretical studies of detonation processes in combustible gaseous mixtures are discussed for a model geometry of large combustion chambers of detonation engines in the case of mixtures of hydrogen and oxygen-enriched air. The effect of geometric characteristics on the operation of pulse detonation engines is analyzed. In particular, the propagation of detonation waves in tubes of small diameter to larger volumes and the evolution of detonation under the action of converging shock waves are considered.