Fundamentals of rotating detonations

A rotating detonation propagating at nearly Chapman–Jouguet velocity is numerically stabilized on a two-dimensional simple chemistry flow model. Under purely axial injection of a combustible mixture from the head end of a toroidal section of coaxial cylinders, the rotating detonation is proven to give no average angular momentum at any cross section, giving an axial flow. The detonation wavelet connected with an oblique shock wave ensuing to the downstream has a feature of unconfined detonation, causing a deficit in its propagation velocity. Due to Kelvin–Helmholtz instability existing on the interface of an injected combustible, unburnt gas pockets are formed to enter the junction between the detonation and oblique shock waves, generating strong explosions propagating to both directions. Calculated specific impulse is as high as 4,700 s.      

The propagation mechanism of high speed turbulent deflagrations

The propagation regimes of combustion waves in a 30 cm by 30 cm square cross–sectioned tube with an obstacle array of staggered vertical cylindrical rods (with BR=0.41 and BR=0.19) are investigated. Mixtures of hydrogen, ethylene, propane, and methane with air at ambient conditions over a range of equivalence ratios are used. In contrast to the previous results obtained in circular cross–sectioned tubes, it is found that only the quasi–detonation regime and the slow turbulent deflagration regimes are observed for ethylene–air and for propane–air. The transition from the quasi–detonation regime to the slow turbulent deflagration regime occurs at (where D is the tube “diameter” and is the detonation cell size). When , the quasi–detonation velocities that are observed are similar to those in unobstructed smooth tubes. For hydrogen–air mixtures, it is found that there is a gradual transition from the quasi–detonation regime to the high speed turbulent deflagration regime. The high speed turbulent deflagration regime is also observed for methane–air mixtures near stoichiometric composition. This regime was previously interpreted as the “choking” regime in circular tubes with orifice plate obstacles. Presently, it is proposed that the propagation mechanism of these high speed turbulent deflagrations is similar to that of Chapman–Jouguet detonations and quasi-detonations. As well, it is observed that there exists unstable flame propagation at the lean limit where . The local velocity fluctuates significantly about an averaged velocity for hydrogen–air, ethylene–air, and propane–air mixtures. Unstable flame propagation is also observed for the entire range of high speed turbulent deflagrations in methane–air mixtures. It is proposed that these fluctuations are due to quenching of the combustion front due to turbulent mixing. Quenched pockets of unburned reactants are swept downstream, and the subsequent explosion serves to overdrive the combustion front. The present study indicates that the dependence on the propagation mechanisms on obstacle geometry can be exploited to elucidate the different complex mechanisms of supersonic combustion waves. Received 5 November 2001 / Accepted 12 June 2002 / Published online 4 November 2002 Correspondence to: J. Chao (e-mail: jenny.chao@mail.mcgill.ca) An abridged version of this paper was presented at the 18th Int. Colloquium on the Dynamics of Explosions and Reactive Systems at Seattle, USA, from July 29 to August 3, 2001.     

A study on jet initiation of detonation using multiple tubes

A detonator consisting of a dense bundle of small-diameter tubes (4.4–19 mm) is tested experimentally using stoichiometric mixtures of hydrogen–oxygen and hydrogen–air. Tests are conducted in a 5,200-mm long detonation tube fitted with a schlieren photograph section and smoked foil to record the deflagration to detonation (DDT) transition. It is confirmed that the flame jet emanating from the tube assembly causes detonation initiation immediately downstream of the detonator, with little dependence on the size of the detonation tube. For the fuel–air mixture, the insertion of Shchelkin spirals into each of the smaller tubes enhances the development of the turbulent flame jet, leading to a shorter DDT distance. Multi-point spark ignition is also shown to provide a further reduction in the DDT distance compared to single-point ignition. PACS 47.40.-x; 47.40.Nm; 47.70.Fw; 82.40.-g; 82.40.Fp     

Detonation Wave Propagation in Rotational Gas Flows

This paper studies the propagation of detonation and shock waves in vortex gas flows, in which the initial pressure, density, and velocity are generally functions of the coordinate — the distance from the symmetry axis. Rotational axisymmetric flow having a transverse velocity component in addition to a nonuniform longitudinal velocity is considered. The possibility of propagation of Chapman–Jouguet detonation waves in rotating flows is analyzed. A necessary conditions for the existence of a Chapman–Jouguet wave is obtained.     

Influence of Molecular Characteristics of a Substance on Detonation Phenomena

In the present study, the molecular-dynamics method has been used to examine the influence of the thermal effect of the chemical reaction on processes in a detonating molecular crystal (propagation velocity and structure of the detonation wave, delay time of the chemical reaction, and energy macrocharacteristics of the crystal in the disturbed region). Molecular-dynamics data are compared with predictions of the continuum theory of detonation; in particular, fulfillment of the Chapman–Jouguet condition is verified.     

固体炸药爆轰温度的实验研究

用光电比色高温计测定了固体炸药TNT、Tetryl、PETN的爆轰温度及爆轰前沿和透明液体相互作用后的爆轰产物的温度。为了讨论实验误差,还研究了爆轰温度随密度的变化以及不同透明液体对爆温测量的影响。     

Experimental observation of the onset of detonation downstream of a perforated plate

In this study, the onset of detonation downstream of a perforated plate subsequent to the reflection of a Chapman–Jouguet detonation upstream is investigated. The experiments were performed with C₃H₈ + 5O₂ and C₂H₂+2.5O₂+70%Ar. The former has a much more irregular transverse wave pattern whereas the latter is known to have a piecewise laminar structure with a regular cellular structure. The onset of detonation phenomenon was found to be significantly different for the two mixtures. For the high argon diluted mixtures, the onset of detonation occurs in the vicinity downstream of the perforated plate. However, if the onset of detonation does not occur close to the plate, the precursor shock decouples from the reaction zone and a deflagration results. For the propane–oxygen mixtures, the onset of detonation is found to occur relatively far from the perforated plate at critical conditions. The major difference between these two mixtures is that the metastable turbulent reaction front can be maintained for relatively long distances for the propane–oxygen mixture. This turbulent metastable regime is also observed to be able to maintain a relatively constant propagation velocity for many channel widths prior to the onset of detonation. For the propane–oxygen mixtures, the onset is caused by a strong local explosion within the turbulent reaction zone.     

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。     

Detonation wave initiated by explosive condensation of supersaturated carbon vapor

An experimental study of the influence of condensation of supersaturated carbon vapor formed behind reflected shock waves on the process of propagation of a shock wave and formation of a detonation wave of condensation is carried out. Highly supersaturated carbon vapor was formed from thermal decay of unstable carbon suboxide C₃O₂ → C + 2CO behind a shock wave in mixtures containing 10–30% C₃O₂ in Ar. This reaction was followed by fast growth of condensed carbon particles, accompanied by heat release. Experiments have shown a considerable temperature and pressure increase in the narrow zone behind the wave front, resulting in shock wave amplification and transition to a detonation-like regime. An analysis of the kinetics and heat release in the given conditions and calculations based upon one-dimensional detonation theory have shown that in a mixture of 10% C₃O₂ + Ar, insufficient heat release resulted in a regime of “overdriven detonation”. In a mixture of 20% C₃O₂ + Ar a very good coincidence of measured values of pressure and wave velocity with calculated Chapman–Jouguet parameters is observed. In a 30% C₃O₂ + Ar mixture, an excess heat release caused a slow down of the effective condensation rate and a regime of “underdriven detonation” is observed.     

Head-on Collision of a Detonation with a Planar Shock Wave

The phenomenon that occurs when a Chapman–Jouguet (CJ) detonation collides with a shock wave is discussed. Assuming a one-dimensional steady wave configuration analogous to a planar shock–shock frontal interaction, analytical solutions of the Rankine–Hugoniot relationships for the transmitted detonation and the transmitted shock are obtained by matching the pressure and particle velocity at the contact surface. The analytical results indicate that there exist three possible regions of solutions, i.e. the transmitted detonation can have either strong, weak or CJ solution, depending on the incident detonation and shock strengths. On the other hand, if we impose the transmitted detonation to have a CJ solution followed by a rarefaction fan, the boundary conditions are also satisfied at the contact surface. The existence of these multiple solutions is verified by an experimental investigation. It is found that the experimental results agree well with those predicted by the second wave interaction model and that the transmitted detonation is a CJ detonation. Unsteady numerical simulations of the reactive Euler equations with both simple one-step Arrhenius kinetic and chain-branching kinetic models are also carried out to look at the transient phenomena and at the influence of a finite reaction thickness of a detonation wave on the problem of head-on collision with a shock. From all the computational results, a relaxation process consisting of a quasi-steady period and an overshoot for the transmitted detonation subsequent to the head-on collisions can be observed, followed by the asymptotic decay to a CJ detonation as predicted theoretically. For unstable pulsating detonations, it is found that, due to the increase in the thermodynamic state of the reactive mixture caused by the shock, the transmitted pulsating detonation can become more stable with smaller amplitude and period oscillation. These observations are in good agreement with experimental evidence obtained from smoked foils where there is a significant decrease in the detonation cell size after a region of relaxation when the detonation collides head-on with a shock wave.     

Propagation Regimes of Self-Supported Light-Detonation Waves

The light-detonation wave structure is investigated. It is shown that self-supported laser radiation absorption waves can propagate in the Jouguet detonation or undercompressed detonation regimes. The conditions of realization of these regimes are found numerically. It is shown that the undercompressed detonation regime is realized if the radiation flux is sufficiently powerful. In the case of a light-detonation wave this regime is theoretically detected and investigated for the first time.     

一类爆轰合成用乳化炸药的爆轰反应特征

结合热分解特性、爆轰产物状态及数值计算探讨所制备的含Fe、Mn(Zn)元素乳化炸药的爆轰反 应特征。对该系列乳化炸药及其爆轰产物分别进行DSC和DTG实验、XRD检测和TEM 表征,通过比较不 同类型炸药及其爆轰产物的热分解特征、爆轰产物的成分和形貌、晶型畸变度等研究该类炸药爆轰反应特征; 并通过数值计算研究和佐证了不同温度和压强状态下,爆轰固体产物可能存在状态。结果表明:硝酸铵有利 于炸药爆轰时形成相对比较均匀和平稳的爆轰反应结构,而这种结构有利于可重复性合成比较单一和均匀 的爆轰产物。高密度炸药的爆轰产物比低密度炸药的相对纯净。低密度炸药不完全爆轰,导致了爆轰产物杂 质较多;数值计算结果表明,爆轰固体产物分布相图可以辅助分析爆轰固体产物可能存在状态及Mn(Zn)的 爆轰合成机制。     

HMX/TNT炸药爆速与曲率及组分关系实验研究

为了确定爆轰波法向速度Dn与当地曲率κ的定量关系,用光电联合测试法研究质量配比分别为60/40、50/50及40/60时HMX/TNT炸药的Dn-κ关系.结果表明,爆轰波延滞距离z随TNT含量的增加而增大;爆轰波延滞距离z随著炸药密度P的增大而减小;随着TNT的含量增加,Dn-κ曲线的斜率逐渐增大,且斜率增大的速率为正...     

Existence of Solutions for Steady Detonation of Gas Suspensions

The existence of solutions of the traveling–wave type is studied for a system of equations that describes a one–dimensional motion of a suspension of evaporating particles in a viscous and heat–conducting chemically reacting gas. Using topological methods, it is shown that solutions corresponding to weak, strong, and Chapman—Jouguet detonation exist under certain restrictions on energy release and mass transfer.     

Optimization study of spray detonation initiation by electric discharges

Development of air-breathing pulse detonation engines is faced with a challenging problem of detonation initiation in fuel sprays at distances feasible for propulsion applications. Extensive experimental study on initiation of a confined n-hexane spray detonation in air by electric discharges is reported. It is found that for direct initiation of spray detonation with minimal energy requirements (1) it is worth to use one discharger located near the closed end of a detonation tube and at least one additional discharger downstream from it to be triggered in-phase with primary shock wave arrival; (2) the discharge area should be properly insulated to avoid electric loss to metal tube walls; (3) discharge duration should be minimized to at least 50 μs; (4) discharge channel should preferably occupy a large portion of a tube cross-section; (5) test tube should be preferably of a diameter close to the limiting tube diameter; (6) gradual transition between the volume with electric discharger and the tube should be used; and (7) a powerful electric discharger utilized for generating a primary shock wave can be replaced by a primary shock wave generator comprising a relatively low-energy electric discharger, Shchelkin spiral, and tube coil. With all these principles implemented, the rated electric energy of about 100 J was required to initiate n-hexane spray–air detonation in a 28-mm tube at a distance of about 1 m from the atomizer. PACS 02.60.Cb; 05.10.Ln; 47.11.+j; 47.15.Cb; 47.40.Nm This paper was based on work that was presented at the 19th Inter-national Colloquium on the Dynamics of Explosions and Reactive Systems, Hakone, Japan, July 27 - August 1, 2003     

快速热点火熔奥梯铝炸药燃烧转爆轰实验研究

以熔铸型含铝混合炸药熔奥梯铝为对象,研究铸装含铝混合炸药快速热点火后的燃烧转爆轰特性。建立了快速热点火燃烧转爆轰实验平台,由实验装置(加热装置、约束钢管、炸药)、压力测试系统、光纤测速系统组成;加热装置加热15 mm厚45钢钢板,峰值温度大于1 100℃,温升速率为85～95℃/s。开展了快速热点火带壳熔奥梯铝炸药燃烧转爆轰实验,由加热装置加热约束钢管内熔奥梯铝炸药,炸药化学反应阵面压力和传播速度分别由压电性高压压力传感器和光纤探针测定;实测阵面压力约1 GPa,传播速度最大约2 600 m/s。由光纤数据获得炸药化学反应阵面传播轨迹,通过特征线方法获得冲击形成点,半定量给出冲击形成距离大于850 mm;并比较了管体破片质量实测值与炸药完全爆轰时破片平均质量计算值,实测值远小于计算值。综合实测化学反应阵面传播速度和压力、冲击形成距离分析、破片质量比较,可确定熔奥梯铝炸药没有发生完全爆轰,其化学反应状态为爆燃。另外,采用Adams和Pack模型、CJ燃烧模型,都能够半定量的预估冲击形成距离和燃烧波后压力,为实验设计提供依据,但CJ燃烧模型的计算结果更接近于实测值。     

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.     

PETN、RDX和HMX炸药爆轰参数的数值模拟

用吉布斯自由能最小原理,通过解化学平衡方程组,求解PETN、RDX和HMX炸药爆轰产物系统的平衡组分,计算结果与用BKW和LJD方法计算的结果相近。用自编的程序从碳的石墨相、金刚石相、类石墨液相和类金刚石液相4种相态中确定出炸药爆轰产物中游离碳更可能存在的相态,并用此相态计算碳的吉布斯自由能。以WCA状态方程作为爆轰气相产物的物态方程,对PETN、RDX和HMX炸药爆轰参数作了预言,爆轰CJ点的爆速、爆压和爆温的计算结果与实验值吻合得很好。     

Experimental technique for generating fast high-density shock waves with phased linear explosive shock tubes

The sequential detonation of a layer of explosive surrounding a pressurized tube can be used to generate fast, high-density shock waves by means of a piston-like implosive pinch travelling at the detonation velocity of the explosive. A novel technique has been developed to extend the regime of operation to piston velocities greater than the detonation velocity of known explosives. This technique consists of cutting a slit in the tamper of a conventional explosive shock tube and introducing a phased detonation wave into the explosive cladding. Preliminary results indicate that quasi-steady shocks can be generated in helium with velocities between 13–17 km/s for initial fill pressures of 6.9 MPa.     

钝感炸药的超压爆轰与冲击起爆过程数值模拟

采用Hybrid反应率结合修正的JWL方程,研究了LX-17、超细TATB等钝感炸药的冲击起爆（SDT）过程,并计算了爆轰波的对碰现象。结果表明,该方法计算钝感炸药的冲击起爆过程与实验数据符合较好;计算爆轰波对碰区的峰值压力提高了10％。