Helium dilution for ram accelerator operation

Experimental detonation characteristics (detonability limits and detonation velocities) of methane-oxygen-helium mixtures at initial pressures of up to 5 MPa were measured in a 90 mm caliber, 11.7 m long (130 calibers) smooth-bore detonation tube. Stoichiometric as well as fuel-rich mixtures were investigated in order to provide performance data for ram accelerator applications. The experimental results were used to adjust and validate calculations of the Chapman-Jouguet detonation characteristics by means of a thermochemical code based on various real gas equations of state. On the basis of the detonation velocity data, a series of intermolecular parameters involved in the thermochemical code was determined. Furthermore, the investigation enabled to determine of the upper detonable area of these dense ternary mixtures under the present experimental conditions. Received 25 February 2000 / Accepted 24 January 2001     

Investigation of the detonation regimes in gaseous mixtures with suspended starch particles

The existence of a secondary discontinuity at the rear of a detonation front shown in experiments by Peraldi and Veyssiere (1986) in stoichiometric hydrogen-oxygen mixtures with suspended 20-m starch particles has not been explained satisfactorily. Recently Veyssiere et al. (1997) analyzed these results using a one-dimensional (1-D) numerical model, and concluded that the heat release rate provided by the burning of starch particles in gaseous detonation products is too weak to support a double-front detonation (DFD), in contrast to the case of hybrid mixtures of hydrogen-air with suspended aluminium particles in which a double-front detonation structure was observed by Veyssiere (1986). A two-dimensional (2-D) numerical model was used in the present work to investigate abovementioned experimental results for hybrid mixtures with starch particles. The formation and propagation of the detonation has been examined in the geometry similar to the experimental tube of Peraldi and Veyssiere (1986), which has an area change after 2 m of propagation from the ignition point from a 69 mm dia. section to a 53 mm 53 mm square cross section corresponding to a 33% area contraction. It is shown that the detonation propagation regime in these experiments has a different nature from the double-front detonation observed in hybrid mixtures with aluminium particles. The detonation propagates as a pseudo-gas detonation (PGD) because starch particles release their heat downstream of the CJ plane giving rise to a non-stationary compression wave. The discontinuity wave at the rear of the detonation front is due to the interaction of the leading detonation front with the tube contraction, and is detected at the farthest pressure gauge location because the tube length is insufficient for the perturbation generated by the tube contraction to decay. Thus, numerical simulations explain experimental observations made by Peraldi and Veyssiere (1986). Received 5 July 1997 / Accepted 13 July 1998     

About the formulation,verification and validation of the hypersonic flow solver Eilmer

We describe the formulation of the gas dynamics and high‐temperature thermochemical modules of the Eilmer code, an open‐source Navier–Stokes solver for transient compressible flow in two and three dimensions. The core gas dynamics formulation is based on finite‐volume cells, and the thermochemical effects are handled with specialised updating schemes that are coupled into the overall time‐stepping scheme. Verification of the code is explored via a number of case studies that use analytic and semi‐analytic solutions as comparison. These include both smooth and shocked flows and are used to demonstrate the order of spatial accuracy of the code. Cases include manufactured solutions for rather abstract inviscid and viscous flow, an idealised detonation wave supported by a curved body, and the transient flow of an idealised but high‐performance shock tube. Validation of the inviscid gas dynamics and thermochemical models is then explored using data from a selection of experimental studies. These studies include ballistic range experiments with chemically‐inert noble gases and high‐temperature chemically‐reacting air. These comparisons show that the code performs well and they provide a lesson in considering a range of experimental data rather than relying upon isolated data points for validation. These verification and validation cases are described in full detail and will be useful for other code developers of high‐temperature compressible flow solvers. Copyright © 2013 John Wiley & Sons, Ltd.     

Detonation wave initiation of ram accelerator propellants

The current ram accelerator operations have shown that data on the ability of the propellants to detonate are required. Previous studies examined the efficacy of initiation techniques based on piston impact. The purpose of the present work is to analyze the effects of detonation wave transmission from a detonating mixture into a low sensitivity mixture. One-dimensional modeling based on the analysis of pressure vs particle velocity for the mixtures is used to interpret experimental data. Furthermore, calculations based on chemical kinetics (CHEMKIN code) are provided. Experimental data together with the modeling of the detonation transmission provide some new insight into the limiting conditions necessary to establish a Chapman-Jouguet (CJ) wave in a detonable mixture. Received 11 January 2000 / Accepted 15 September 2000     

Detonation waves in trinitrotoluene

Fabry-Perot, ORVIS, and VISAR laser interferometry are used to obtain nanosecond time resolved particle velocity histories of the free surfaces of copper and tantalum discs accelerated by detonating trinitrotoluene (TNT) charges and of the interfaces between TNT detonation products and lithium fluoride crystals. TNT detonation reaction zone profiles are measured for self-sustaining detonation and piston supported overdriven (supracompressed) waves. The experimental records are compared to particle velocity histories calculated using very finely zoned meshes of the exact dimensions with the DYNA2D hydrodynamic code. The Ignition and Growth reactive flow model, which is based on the Zeldovich-von Neumann-D?ring (ZND) theory of detonation, yields excellent agreement with the experimental records for TNT using an unreacted von Neumann spike pressure of 25 GPa, a reaction rate law which releases 90% of the chemical energy within 80 ns and the remaining 10% over an additional 200 ns, and a reaction product equation of state fit to cylinder test data assuming a Chapman-Jouguet pressure of 19 GPa. The late time energy release is attributed to diffusion controlled solid carbon particle formation. Received 26 July 1997 / Accepted 29 December 1997     

氢气/丙烷/空气预混气体爆轰性能的实验研究

通过采用压力传感器和烟灰板两种测试设备,开展了常温常压下氢气/丙烷和空气混合气体爆轰性能的实验研究。实验过程中观察到自持爆轰波,爆轰速度比值在0.99~1之间,爆轰压力比值在0.8~1.2之间。爆轰胞格尺寸在10~50 mm范围内,建立了爆轰胞格尺寸和化学诱导长度的关系式。随着丙烷不断添加,爆轰速度减小,而爆轰压力和胞格尺寸增加。这种变化趋势起初较快,而后变缓。因为起初氢气摩尔分数较大,混合气体趋向于氢气/空气的爆轰性能;而后因丙烷摩尔质量较大,丙烷逐渐起主要作用,混合气体表现出丙烷/空气的爆轰性能。     

液体碳氢燃料云雾爆轰特性的实验研究

采用升降法和烟迹技术在立式激波管中分别实测了液态燃料（环氧丙烷、硝酸异丙酯、己烷、C5~C6、庚烷、癸烷）与空气混合物直接起爆的临界起爆能和胞格尺寸。数据表明,气液两相云雾爆轰的临界起爆能与当量比呈U形曲线关系,这与气相爆轰得到的结论是一致的;临界起爆能的最小值并不是对应于等化学当量的混合物而是偏向于富燃料;根据三波点运动的烟迹记录,分析了云雾爆轰作用机制,认为液滴的碎解、汽化过程以及燃烧区前导是控制气液两相云雾爆轰的主要步骤。此外,还测定了无限空间下可燃气云的临界起爆能,并将激波管内得到的临界起爆能数据外推到无约束气云的临界起爆能,理论推算结果与实验值吻合较好。     

Simulation of unsteady hypersonic combustion around projectiles in an expansion tube

The temporal evolution of combustion flowfields established by the interaction between wedge-shaped bodies and explosive hydrogen-oxygen-nitrogen mixtures accelerated to hypersonic speeds in an expansion tube is investigated. The analysis is carried out using a fully implicit, time-accurate, computational fluid dynamics code that we recently developed to solve the Navier-Stokes equations for a chemically reacting gas mixture. The numerical results are compared with experimental data from the Stanford University expansion tube for two different gas mixtures at Mach numbers of 4.2 and 5.2. The experimental work showed that flow unstart occurred for both the Mach 4.2 cases. These results are reproduced by our numerical simulations and, more significantly, the causes for unstart are explained. For the Mach 5.2 mixtures, the experiments and numerical simulations both produced stable combustion. However, the computations indicate that in one case the experimental data were obtained during the transient phase of the flow; that is, before steady state had been attained. Received 7 February 2000/ Accepted 20 February 2001     

Effect of scale on the onset of detonations

Critical conditions for onset of detonations are compared at (1) two significantly different scales, (2) for a range of -air mixtures diluted with C, O, and (3) for two types of geometry – one a long obstructed channel and the other a room with a relatively small aspect ratios. For the range of scales, mixtures, and initial conditions tested, the detonation cell size was shown to be a reliable scaling parameter for characterization of detonation onset conditions. An experimental correlation is suggested for the critical detonation onset conditions. This correlation is based on a wide variety of available experimental data on DDT in mixtures of hydrogen and hydrocarbon fuels with air and on the use of detonation cell size as a scaling parameter characterizing the mixture. Received 14 November 1999 / Accepted 16 February 2000     

一点起爆半球形装药装置中散心爆轰波传播的数值模拟研究

运用自行研制的二维流体动力学程序TDY2D,对一点起爆半球壳装药装置中散心爆轰波的传播过程进行数值模拟计算.对冲击波到达炸药和飞层各界面的波形的计算值与实验值进行了对比,两者符合较好,从而验证了该程序的准确性和有效性;对爆轰波的传播过程进行了分析研究,获得了一些散心爆轰波传播的规律性认识,为进一步研究散心爆轰波特性提供了数值分析基础.     

2021-08期封面

铝粉反应模型是对悬浮铝粉尘气-固两相爆轰进行数值模拟研究的关键。通过考虑铝粉燃烧产物氧化铝（Al₂O₃）在高温下的分解吸热反应,改进了铝粉的扩散燃烧模型。将该模型嵌入到三维的气-固两相爆轰数值计算程序中,分别对铝粉/空气混合物以及铝粉/氧气混合物的爆轰进行了数值模拟,计算得到的稳定爆轰波速度与实验结果、文献值均吻合较好,误差小于5.5%,表明改进的铝粉反应模型适用于不同氧化气体氛围中铝粉尘爆轰的模拟计算。此外,对两相爆轰参数及爆轰流场的物理量分布进行分析,获得了铝粉反应模型对爆轰波结构的影响规律。     

Experimental investigation into the detonation characteristics of hybrid RDX–ethylene–air mixtures

An experimental study is conducted to determine the detonation characteristics of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) particles dispersed in a gaseous fuel air mixture in a vertical detonation tube with an inner diameter of 200 mm and a height of 5400 mm. Experiments are performed in both ethylene–air mixtures and RDX–ethylene–air hybrid mixtures. The detonation front pressure and velocity are measured with six pressure transducers along the detonation tube. The results show that the addition of RDX assists 4.0 vol.% ethylene–air mixtures in achieving detonation. The detonation front pressure increases noticeably with dust concentration up to \(474\hbox { g/m}^{3}\) in the RDX–ethylene–air hybrid mixtures, but the velocity only increases slightly. The cellular structures of RDX–ethylene–air hybrid mixtures and ethylene–air mixtures were obtained with the use of smoked foils and exhibit irregular structures. It is found that the measured cell size has a U-shaped curve with respect to RDX concentration.     

Detonability of fuel-oxygen and fuel-air mixtures

An analysis of theoretical models and experimental investigations of the detonability of unconfined detonation in uniform gaseous mixtures shows a disparity in results. The present study is limited to propane, acetylene and methane diluted with oxygen or air in variable proportions and initial pressures at ambient temperature conditions. Because of the disparity in results, a simple and general formulation of critical initiation energy for gaseous detonations has been investigated. The problem has been formulated using the conservation equation of total energy enclosed by the shock. From this, a simple form for the critical energy has been deduced. This approach leads to a good simulation in uniform mixtures, regardless of initiation conditions. Some applications are presented in this paper. A new experimental study on the detonability of methane/oxygen mixtures diluted with propane and/or nitrogen is reported. The gaseous mixtures are confined in a cylindrical vessel. The initial conditions are various equivalence ratio and pressure under room temperature. In the case of methane/oxygen mixtures, the predetonation radius varies directly with the cell width. The constant ratio is in the order of 18, slightly different from the classical relation R _c= 20λ. For propane the slope variation of the critical energy versus initial pressure depends on the dilution. We have compared the critical energy obtained by several authors with the theoretical values. Fuel ratio and initial pressure are the chosen parameters. These comparisons show that the formulation allows for the prediction of the critical energy of detonation of uniform mixtures with a good estimation range. The correlation between the different geometries has been deduced and a test has been conducted as well in the case of stoichiometric methane/oxygen and acetylene/oxygen mixtures versus initial pressure for a cylindrical detonation. Received 9 January 1996 / Accepted 24 January 1997     

A double-front structure of detonation wave as the result of phase transitions

Using thermochemical code calculations, we show that the nanographite–nanodiamond phase transition, which may occur in the detonation products of a number of carbon containing explosives, can affect the detonation properties and can cause a specific detonation regime with some unusual peculiarities. Among them, we first note the failure of the Chapman–Jouguet condition and the presence of the sonic plane, where the Mach number is equal to unity, in a detonation product expansion wave at a lower pressure than that at the Chapman–Jouguet point. The peculiarities of this detonation regime are demonstrated by the example of TNT, HNS, and RDX. The computed detonation velocities are in excellent agreement with experiments over a wide range of initial charge densities for all of the investigated explosives. The results of this work allow one to explain, e.g., contradictory experimental data on the detonation pressure and on the length of the reaction zone for TNT. We believe that some other solid–solid, solid–liquid, and liquid–liquid phase transformations in the detonation products may also cause a detonation regime with the same features as shown here for the nanographite–nanodiamond transition. We suggest a computational study that should facilitate proposing detonation experiments strongly arguing in favor of the model presented. PACS 47.40.-x; 47.40.Rs; 64.70.-p; 64.70.Kb; 05.70.-a; 05.70-.CeThis paper was based on the work that was presented at the 19th International Colloquium on the Dynamics of Explosions and Reactive Systems, Hakone, Japan, July 27–August 1, 2003.     

Investigation of detonation initiation in aluminium suspensions

Detonation initiation is investigated in aluminium/oxygen and aluminium/air mixtures. Critical conditions for initiation of spherical detonations are examined in analogy with the criteria defined for gaseous mixtures, which correlate critical parameters of detonation initiation to the characteristic size of the cellular structure. However, experimental data on the detonation cell size in these two-phase mixtures are very scarce, on account of the difficulty to perform large-scale experiments. Therefore, 2D numerical simulations of the detonation cellular structure have been undertaken, with the same combustion model for Al/air and Al/O₂ mixtures. The cell size is found to be λ = 37.5 cm for a rich (r = 1.61) aluminium–air mixture, and λ = 7.5 cm for a stoichiometric aluminium-oxygen mixture, which is in reasonable agreement with available experimental data. Calculations performed in large-scale configurations (up to 25 m in length and 1.5 m in lateral direction) suggest that the critical initiation energy and predetonation radius for direct initiation of the unconfined detonation in the aluminium–air mixture are, respectively, 10 kg of TNT and 8 m. Moreover, numerical simulations reveal that the structure of the detonation wave behind the leading front is even more complicated than in pure gaseous mixtures, due to two-phase flow effects. 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.     

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     

Response of critical tube diameter phenomenon to small perturbations for gaseous detonations

In this experimental study, the critical tube diameter phenomenon of gaseous detonations is investigated in both stable and unstable mixtures with focus on the failure mechanism. It was previously postulated that in unstable mixtures, where the cellular detonation front is highly irregular, the failure is caused by the suppression of local re-initiation centers linked to the dynamics of instabilities. In stable mixtures, typically with high argon dilution, the detonation structure is very regular and the failure mode is attributed to the excessive curvature of the global front. In order to differentiate between these two failure mechanisms, flow perturbations are introduced by placing an obstacle resulting in a minimal blockage ratio of approximately 8 %. The obstacle is placed at the tube exit, before the detonation diffraction. Results show that the perturbations caused by the obstacle only have an effect on undiluted (i.e., unstable) mixtures, causing a decrease in the minimum initial pressure required for successful detonation transmission. This thus demonstrates that local hydrodynamic instabilities play an important role for the critical tube diameter phenomenon in undiluted, unstable mixtures. In contrast, the results for the stable, argon-diluted mixture exhibit little variation in critical initial pressure between the perturbed and unperturbed cases. This can be attributed to the minimal effect of the perturbations on global curvature for the emergent detonation wave. The geometry of the perturbation is also tested, while holding the blockage area constant, by varying the number and position of the obstacle(s). The results demonstrate that the transmission of a detonation is independent of the blockage geometry and is only a function of its imposed blockage area. Consequently, the change in required minimum pressure for transmission shows an identical behavior in unstable mixtures for different perturbation geometries while the transmission characteristics of the stable mixture remain unaffected.     

Experimental and numerical studies on transmission of gaseous detonation to a less sensitive mixture

A phenomenon of detonation transmission from one gaseous mixture (donor) to another of lower sensitivity (acceptor) was studied experimentally and numerically. The objective was to study effects of a donor mixture length and acceptor mixture sensitivity on the possibility of detonation transmission. Experiments were carried out in detonation tube 9.5–12 m long and 174 mm id. Three types of donor mixtures were used in the driver: stoichiometric acetylene/air, stoichiometric hydrogen/air, and 20% of hydrogen/air. Air mixtures with 14–29.6% of hydrogen were used as acceptors. Driver length varied from 0.17 to 5.6 m. Detonation transmission was studied for an abrupt opening of interface between two mixtures. Series of 1D and 2D calculations were made to simulate the problem numerically. Both, results of experiments and calculations revealed a set of parameters that effect transmission process. Critical conditions were determined as minimum driver length expressed in terms of characteristic chemical reaction length scales of acceptor mixture. They were shown to depend on differences in reaction rates and energy contents of donor and acceptor mixture. Received 6 January 1997 / Accepted 20 March 1997