Relaxation of overdriven detonation waves with finite reaction rate

A numerical study is made of the interaction of a detonation wave having finite reaction velocity with a rarefaction wave of different intensity which approaches it from the rear, for the Zeldovich-Neumann-Doring (ZND) model with a single irreversible reaction A B. It is found that, for a fixed value of the parameter characterizing the initial supercompression (depending on the activation energy and the heating value of the mixture), the considered interaction leads either to a gradual relaxation of the detonation wave and its transition to the Chapman-Jouguet (CJ) regime, or to the development of undamped oscillations.Interest in the problems of detonation and supersonic combustion has increased in recent years. This is associated with the appearance and development of new experimental and theoretical techniques; it is also associated with the further development of air-breathing reaction engines, and other practical requirements. The present state of detonation theory is reflected in the survey [1].It has been established [2] that the detonation wave in gases nearly always has a complex nonuniform structure. Transverse disturbances are observed under a wide range of conditions and differ both in amplitude and wavelength. At the same time, behind the detonation leading front there is a region of uncompletely burned gas corresponding to the effective ignition induction period [3]. In spinning detonation the induction period is significantly longer than the heat release period and transverse detonation waves traveling in the induction zone of the head wave appear [3, 4]. Such a secondary detonation wave is free of transverse disturbances. The same is true of the detonation waves observed in the wake behind a body moving at high speed in a combustible medium [5] or in a gas which has been preheated by a shock wave [6].Although it is possible, under favorable conditions, to study in detail the system of discontinuities accompanying detonation, information on the extensive zones in which heat release takes place is scarce, the mechanism of detonation wave autonomy (in particular, the role of the rarefaction zone behind the wave) is not entirely clear, and the fact that, in spite of the complex structure, an autonomous detonation propagates with the CJ velocity calculated on the basis of one-dimensional theory has not yet been explained.In studying the nonlinear phenomena associated with the finite reaction rate it is quite acceptable to investigate only the simple one-dimensional detonation model, with which it is convenient to restrict ourselves to a single effective chemical reaction. This model is particularly reasonable since, in certain cases, the real detonation is virtually one-dimensional.The question of the stability of the one-dimensional detonation wave to disturbances of its structure has been examined by several authors [7–13]. The use of computers makes possible the direct computation of flows with heat release and the study of their properties. This method has been used in [11–13] to study the stability problem for a detonation wave with respect to finite disturbances.In the present paper we present a numerical study of the interaction of a detonation wave having finite chemical reaction rate with a rarefaction wave of different intensity approaching it from the rear for the ZND model with a single irreversible reaction A B. It is found that for a fixed value of the parameter characterizing the difference between detonation and the CJ waves, depending on the activation energy E and the mixture heating value Q_m, the interaction in question leads either to a gradual relaxation of the detonation wave and its transition to the CJ regime (this relaxation may be accompanied by decaying oscillations) or to the appearance of undamped oscillations (the unstable regime). The parameters E and Q_m affect the wave stability differently: with increase of Q_m, the wave is stabilized; with increase of E, it is destabilized. The boundary between the stable and unstable detonation wave propagation regimes is found. This boundary has a weak dependence on the rarefaction wave intensity. Estimates and calculated examples show that the amplitude of the unstable wave oscillations is finite and that the average detonation propagation velocity is close to the CJ velocity computed for the given heating value Qm.The author wishes to thank G. G. Chernyi for his guidance and L. A. Chudov for advice on computational questions.     

Flow of a gas behind a Chapman-Jouguet detonation wave in the vicinity of a line of discontinuity of a surface wave curvature

This paper discusses questions of constructing a solution of the gasdynamic equations near a line of curvature discontinuity at the surface of a detonation wave, propagating under Chapman—Jouguet conditions. It describes the construction of the solution in two cases: in a flow arising with the initiation of a detonation along a half-plane in a quiescent homogeneous combustible gas and in a flow arising with the initiation of a detonation along a half-line under these same conditions.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 120–126, January–February, 1978.     

高-低爆速圆板炸药串联爆轰引起平面爆轰波的变凸现象

为分析高-低爆速圆板炸药于空中串联爆轰时平面爆轰波在传播过程中演变成凸面波的现象,分别对平面爆轰波阵面后爆轰产物状态参数的分布、有效药量与柱面装药几何尺寸的关系、爆轰产物的状态方程及强爆轰关系式进行了讨论。并以100 mm50 mm的TNT与RC炸药串联爆轰为例,描述了平面爆轰波演变为凸面爆轰波的过程,预估了爆轰波的平面范围和波形差。预估结果与实验结果基本符合。     

Transition to detonation in dynamic phase changes

Subsonically propagating phase boundaries (kinks) can be modelled by material discontinuities which satisfy integral conservation laws plus an additional jump condition governing the phase-change kinetics. The necessity of an additional jump condition distinguishes kinks from the conventional shocks which satisfy the Lax criterion. We study stability of kinks with respect to the breakup (splitting) into a sequence of waves. We assume that all conventional shocks are admissible and that admissible kinks are selected by a prescribed kinetic relation. As we show, regardless of a particular choice of the kinetic relation, sufficiently fast-phase boundaries are unstable. The mode of instability includes an emission of a centered Riemann wave followed by a sonic shock (Chapman-Jouguet type phase boundary).     

关于几种异性平面装药爆轰波阵面的描述

对爆炸压接等所用的几种异性平面装药的爆轰波阵面及其传播建立了理论模型,并对依据其初始波形状绘制的任意时刻的爆轰波阵面给出定理性的方法。     

Stability of gas mixture flow with a stabilized detonation wave in a plane channel with a constriction

The stability of a flow with a stabilized detonation wave is studied within the framework of a detailed kinetic mechanism of the chemical interaction. The flow is due to the initiation of detonation combustion of a stoichiometric hydrogen-air mixture that enters into a plane channel with a constriction at a supersonic velocity greater than that of the self-sustained detonation propagation. The flow under consideration is numerically investigated using the software package developed by the authors. It is established that the flow formed in the channel, whose geometric parameters ensure the detonation stabilization in the case of the inflow Mach number M₀ = 5.2, is stable against strong disturbances of a certain type. The effect of an increase in the inflow Mach number and the dustiness of the combustible gas mixture entering into the channel on the stabilization of detonation combustion in the flow is investigated.     

爆轰波碰撞的聚能效应

利用两高爆速导爆索对称布置于药卷两侧,起爆后炸药爆轰波在对称线处汇聚碰撞,当碰撞角度达到一定值时,发生马赫反射,使爆轰压力成倍增加,形成高压、高能量密度区域的聚能效应。本文在爆轰波传播碰撞理论的基础上,通过炸药做功能力和猛度试验验证爆轰波碰撞的聚能效果。做功能力试验结果表明爆轰波碰撞能够增加炸药能量利用率;猛度试验结果表明采用对称起爆技术下的爆轰波碰撞能够改变爆轰波在特定方向上的扩散作用。试验结果与爆轰波入射角的几何关系表明,当高爆速起爆药条与主装药爆速比例在1.15倍以上时,爆轰波碰撞能够达到一定的聚能效果。     

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     

Transition from fast deflagration to detonation under the influence of periodic longitudinal perturbations

A computational and experimental investigation have been carried out to study deflagration to detonation transition under the influence of periodic longitudinal perturbations. The fast deflagration prior to transition is obtained by suppressing the oscillatory structure of a detonation first. In the one-dimensional computational study, the subsequent re-transition is stimulated using periodic density perturbations. The optimal perturbation period to induce transition is of the order of the rea ction time of the detonation structure. In the experiments, re-transition is stimulated using periodic wire screens placed across the channel. The gas mixture used is 2C₂H₂+5O₂+75%Ar. Laser stroboscopic photography showed the generation of longitudinal pressure waves as the leading shock passes through the wire screens. The interactions of the pressure waves with the leading shock and the reaction zone establish coupling for transition to occur. The computational and experimental studies showed that the time required for transition to take place is dependent on the frequency of the applied perturbation. The present results indicate the need to examine deflagration to detonation transition from the point of view of the formation of an organized oscillatory system.     

Transition from stratified to slug regime in countercurrent flow

In many two-phase flow situations the prediction on the conditions likely to instigate the change of flow pattern from the stratified regime to the slug flow condition is important. Since published material on such predictions for countercurrent flow is scarce this paper considers the influencing parameters for these conditions and then uses the data recorded from an experimental test rig to quantify the developed instability criterion equation.     

Inhibition of detonation wave with halogenated compounds

The influence of CF₃Br, CF₂HBr, CF₂HCl and CF₃H on a benchmark mixture composed of stoichiometric H₂−CO−O₂−Ar is experimentally investigated. Several ratios hydrogen/carbon monoxide are studied. For each benchmark mixture, the initial pressure is adjusted in such a way that the detonation cell sizes are quasi identical. The effect of the additives on the detonation velocity and the detonation cellular structure is analyzed. The experiments show that CF₃Br is the best inhibitor and CF₂HBr might be substituted for CF₃Br. CF₃H does not inhibit the detonation wave. Simple chemical kinetics analysis gives us a better understanding of the inhibiting and promoting effect of the halocarbons. 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     

反向起爆模型下的冲击波加载

为了实现对大尺寸材料试件的动态加载,得到与轻气炮加载应力波相同的爆炸加载冲击波,基于叠加原理,提出了利用炸药反向起爆模型完成对可压缩固体材料的冲击波加载。通过联立爆炸产物和可压缩流体的速度-压力曲线以及综合考虑炸药和材料试件各自由边所受稀疏波干扰的情况,从理论上给出了冲击波压力和冲击波加载平台宽度的计算方法。并结合数值模拟,对理论分析结果进行了验证,两者基本一致。

     

氢燃料缓燃向爆震转捩过程中波与火焰的匹配特性

为了解氢燃料爆震过程中压力波与火焰之间相互匹配的特性,在60mm60mm2000mm 方 爆震管内,用氢气和空气混合物进行了单爆震性能研究。在爆震转捩区内布置压力传感器与离子探针,用来 监控压力波和火焰的信号,同时利用高速摄影仪集中拍摄转捩区域。根据压力波和火焰面在爆震管不同时刻 的强度特性、速度特性及位置特性来分析爆震过程中波与火焰匹配的规律。结果表明:压力波和火焰的强度 呈现为相互正反馈匹配性质;缓燃向爆震转捩(DDT)过程中,压力波和火焰的速度表现为相互交替的变化过 程,且缓燃阶段中火焰速度的增幅大于压力波速度的增幅;当火焰面追赶上激波时,产生过爆,火焰面会临时 位于激波前面;在过爆衰减为正常爆震波的过程中,激波在火焰前面。     

Super-equilibrium increase of chemical reaction rate in the detonation front and other effects in the detonation wave initiated by a shock wave

In the present work the problem of detonation wave formation in a shock tube was considered in one-dimensional formulation. The Monte Carlo non-stationary method of statistical simulation (MCNMSS), also known as DSMC, was used for simulation. The method automatically takes into account all details of mass and heat transfer. At an initial moment, the low-pressure channel (LPC) of the shock tube was filled with gas A while the high-pressure chamber (HPC) was filled with gas C. The cross-sections of the HPC and LPC, as well as the temperatures of gases A and C were equal to each other. At the beginning of the simulation the ratio of pressures in the HPC and LPC was equal to 100. It was assumed that chemical reactions $\mathrm{{A}}+\mathrm{{M}} \rightarrow \mathrm{{B}}+\mathrm{{M}}$ ( $\mathrm{{M}}=\mathrm{{A}},\, \mathrm{{B}}$ and $\mathrm{{C}}$ ) took place. The ratio of molecular masses of gases $\mathrm{{A}},\, \mathrm{{B}}$ and $\mathrm{{C}}$ was taken as 20:20:1. Different reaction thresholds were considered. For the case of a low reaction threshold, the velocity of the resulting detonation wave was found to be higher than the Chapman–Jouguet velocity. A region with constant values of flow parameters inside product was observed. An increase of the reaction threshold led to disappearance of this region and gave rise to something similar to an expansion wave, with peaks of flow parameters at the leading part of the detonation wave. The values of these peaks were found to be constant in time. The velocity of the detonation wave became appreciably lower than the Chapman–Jouguet velocity. Further increase of the reaction threshold led to disappearance of detonation. The reactions $\mathrm{{A}}+\mathrm{{B}} \rightarrow \mathrm{{B}}+\mathrm{{B}}$ and $\mathrm{{A}}+\mathrm{{C}}\rightarrow \mathrm{{B}}+\mathrm{{C}}$ turned out to be very important for initiation of detonation.     

Propagation of detonation waves in plane channels with obstacles

The detonation wave propagation in plane channels filled with a stoichiometric hydrogen-air mixture at rest under standard conditions is numerically modeled with account for the actual kinetics of the chemical interaction. The calculations show that the stable cellular structure of the detonation wave formed in a plane channel with parallel walls is not always uniquely determined by its width. The effect of transverse walls and sharp expansion of the channel on the propagation of the cellular detonation wave is studied. The conditions of conservation and restoration of detonation are determined.     

Reinitiation process of detonation wave behind a slit-plate

The propagation phenomenon of a detonation wave is particularly interesting, because the detonation wave is composed of a 3D shock wave system accompanied by a reaction front. Thus, the passage of a detonation wave draws cellular patterns on a soot-covered plate. The pressure and temperature behind the detonation wave are extremely high and may cause serious damages around the wave. Therefore, it is of great significance from a safety-engineering point of view to decay the detonation wave with a short distance from the origin. In the present study, experiments using high-speed schlieren photography are conducted in order to investigate the behaviors of the detonation wave diffracting from two slits. The detonation wave produced in a stoichiometric mixture of hydrogen and oxygen is propagated through the slits, and the behaviors behind the slit-plate are investigated experimentally. When a detonation wave diffracts from the slits, a shock wave is decoupled with a reaction front. Since the two shock waves propagate from the slits interact with each other at the center behind the plate, the detonation wave is reinitiated by generating a hot-spot sufficient to cause local explosions. Furthermore, it is clarified that the shock wave reflected from a tube-wall is also capable of reinitiating the detonation wave. The reinitiation distance of the detonation wave from the slit-plate is correlated using a number of cells emerged from each slit.