Detonation Phenomena Research Articles

Research at the CEA in the field of safety in 2nd and 3rd generation light water reactors

Abstract The research programs at the CEA in the field of safety in nuclear reactors are carried out in a framework of international partnerships. Their purpose is to develop studies on: – The methods allowing for the determination of earthquake hazards and their consequences; – The behaviour of fuel in an accident situation; – The comprehension of deflagration and detonation phenomena of hydrogen and the search for effective prevention methods involving an explosion risk; – The cooling of corium in order to stop its progression in and outside the vessel thereby reducing the risk of perforating the basemat; – The behaviour of the different fission product families according to their volatility for the UO2 and MOX fuels.

Acceleration and heating of metal particles in condensed matter detonation

For condensed explosives, containing metal particle additives, interaction of the detonation shock and reaction zone with solid inclusions leads to high rates of momentum and heat transfer that consequently introduce non-ideal detonation phenomena. During the time scale of the leading detonation shock crossing a particle, the acceleration and heating of metal particles are shown to depend on the volume fraction of particles, dense packing configuration, material density ratio of explosive to solid particles and ratio of particle diameter to detonation reaction-zone length. Dimensional analysis and physical parameter evaluation are used to formalize the factors affecting particle acceleration and heating. Three-dimensional mesoscale calculations are conducted for matrices of spherical metal particles immersed in a liquid explosive for various particle diameter and solid loading conditions, to determine the velocity and temperature transmission factors resulting from shock compression. Results are incorporated as interphase exchange source terms for macroscopic continuum models that can be applied to practical detonation problems involving multi-phase explosives or shock propagation in dense particle-fluid systems.

Shock wave physics and detonation physics — a stimulus for the emergence of numerous new branches in science and engineering

In the period of the Cold War (1945−1991), Shock Wave Physics and Detonation Physics (SWP&DP) — until the beginning of WWII mostly confined to gas dynamics, high-speed aerodynamics, and military technology (such as aero- and terminal ballistics, armor construction, chemical explosions, supersonic gun, and other firearms developments) — quickly developed into a large interdisciplinary field by its own. This rapid expansion was driven by an enormous financial support and two efficient feedbacks: the Terminal Ballistic Cycleand the Research& Development Cycle. Basic knowledge in SWP&DP, initially gained in the Classic Period(from 1808) and further extended in the Post-Classic Period(from the 1930s to present), is now increasingly used also in other branches of Science and Engineering (S&E). However, also independent S&E branches developed, based upon the fundamentals of SWP&DP, many of those developments will be addressed (see Tab. 2). Thus, shock wave and detonation phenomena are now studied within an enormous range of dimensions, covering microscopic, macroscopic, and cosmic dimensions as well as enormous time spans ranging from nano-/picosecond shock durations (such as produced by ultra-short laser pulses) to shock durations that continue for centuries (such as blast waves emitted from ancient supernova explosions). This paper reviews these developments from a historical perspective.

Research of Elastomeric Protective Layers Subjected to Blast Wave

The paper is based on non–linear finite element analysis of the blast wave effects on structures, caused by the detonation of explosive materials. Dynamic response of a structure with and without elastomeric layers subjected to the shock wave produced by the detonation of high explosive materials is presented in this paper. Coupled Euler and Lagrange formulation are used in the finite element analysis of such problems to accurately represent the detonation phenomenon. Research related to blast wave propagation is not only aimed at its effect on structures but also on developing new concepts of protective panels. The research carried out on various structures (such as multi–layer panels) has been performed to find out the most efficient protection against a detonation wave. Tests of multi-layer protective panels ability to absorb the explosion energy were also conducted under field conditions and confirmed in numerical studies. The application of structural protective layers made of elastomeric material significantly reduced the blast wave thanks to dissipation capabilities. Additionally, the shape effect of structural steel elements (streamlined profile) during the interaction process with a shock wave has been also confirmed.

Detonation zone width determination based on uncertainty principle

A phenomenological approach to describing detonation phenomena in high explosives is proposed, according to which the zone of relaxation processes (detonation zone) is treated as an excited quantum-mechanical system in the coherent state. The corresponding definition of the detonation zone width is not related to the kinematic parameters of the detonation wave.

Critical energy for direct initiation of spherical detonations in H 2/N 2O/Ar mixtures

Although the detonation phenomenon in hydrogen–nitrous oxide mixtures is a significant issue for nuclear waste storage facilities and development of propulsion materials, very limited amount of critical energy data for direct initiation – which provides a direct measure of detonability or sensitivity of an explosive mixture − is available in literature. In this study, the critical energies for direct blast initiation of spherical detonations in hydrogen–nitrous oxide–Ar mixtures obtained from laboratory experiments and theoretical predictions at different initial conditions (i.e., different initial pressure, equivalence ratio and amount of argon dilution) are reported. In the experiments, direct initiation is achieved via a spark discharge from a high voltage and low inductance capacitor and the initiation energy is estimated accordingly from the current output. Characteristic detonation cell sizes of hydrogen–nitrous oxide–Ar mixtures are estimated from chemical kinetics using a recently updated reaction mechanism. A correlation expression is developed as a function of initial pressure, argon dilution and equivalence ratio, which is fitted to provide good estimation of the experimental measured data. The direct link between cell size and critical energy for direct blast initiation is then analyzed. Good agreement is found between experimental results and theoretical predictions, which make use of the cell size estimation correlation and the semi-empirical surface energy model. The effects of the initial pressure, equivalence ratio and the amount of Ar dilution on the critical initiation energy H 2–N 2O–Ar mixtures are investigated. By comparing the critical energies with those of H 2–O 2–Ar mixtures, it is shown that H 2–N 2O mixtures are more detonation sensitive with smaller initiation energies than H 2–O 2 mixtures at the same initial pressure, equivalence ratio and amount of argon dilution, except for higher diluted condition with amount of argon in the mixture above 20%. Attempt is made to explain the critical energy variation and comparison between the two H 2–N 2O–Ar and H 2–O 2–Ar mixtures from the induction length analysis and detonation instability consideration.

Application of the CE/SE Method to a Two-Phase Detonation Model in Porous Media

We extend the conservation-element and solution-element method to simulate a two-phase detonation model in porous media. The accuracy of the method is validated by calculating an inert compaction problem. The main characteristics of piston-driven detonation phenomena, including the compaction wave, the onset of combustion, and the transition to detonation, could be predicted successfully.

219301 凝縮系高エネルギー物質の爆轟現象に関する研究(OS13 安全に寄与する熱工学1,オーガナイズド・セッション)

Understanding of detonation phenomena is important on physical hazard analysis of high-energetic materials. This paper describes our study on the estimation method of the thermodynamic state variables for simulating the detonation phenomena by CFD code.

Numerical simulation of propane detonation in medium and large scale geometries

A modelling strategy has been developed for consequence analysis of medium and large scale gaseous detonation. The model is based on the solution of Euler equations with one-step chemistry. The Van Leer flux limited method which is a total variation diminishing scheme is used for shock capturing. Preliminary calculations were firstly conducted for small domains with fine grids which resolve the wave, relatively coarse grids which have less than 10 grids across the wave and coarse grids in which the minimum grid size is larger than the wave thickness to ensure that the reaction scheme has been properly tuned to capture the correct detonation pressure, temperature and velocity in the resolutions used in the different cases. The model was firstly tested against a medium scale detonation test in a shock tube with U-bends. Reasonably good agreement is achieved on detonation pressure and mean shock wave velocities at different measuring segments of the tube. Following the validation, the detonation of a hypothetical planar propane–air cloud is simulated. The predictions uncovered some interesting features of such large scale detonation phenomena which are of significance in the safety context, especially for accidental investigations. The findings from the present analysis are in line with the forensic evidence on damages in some historic accidents and challenges previous analysis of a major accident in which forensic evidence suggested localised detonation but was considered as the consequence of fire storms by the investigation team.

Oblique detonation waves stabilized in rectangular-cross-section bent tubes

Oblique detonation waves, which are generated by a fundamental detonation phenomenon occurring in bent tubes, may be applied to fuel combustion in high-efficiency engines such as a pulse detonation engine (PDE) and a rotating detonation engine (RDE). The present study has experimentally demonstrated that steady-state oblique detonation waves propagated stably through rectangular-cross-section bent tubes by visualizing these waves using a high-speed camera and the shadowgraph method. The oblique detonation waves were stabilized under the conditions of high initial pressure and a large curvature radius of the inside wall of the rectangular-cross-section bent tube. The geometrical shapes of the stabilized oblique detonation waves were calculated, and the results of the calculation were in good agreement with those of our experiment. Moreover, it was experimentally shown that the critical condition under which steady-state oblique detonation waves can stably propagate through the rectangular-cross-section bent tubes was the curvature radius of the inside wall of the rectangular-cross-section bent tube equivalent to 14–40 times the cell width.

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.

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.

Theoretical Notes on the Mathematical Modelling of Gaseous Detonations Using Boltzmann Equation

In this study, we present some theoretical notes on the use of the Boltzmann equation in computing detonation of combustible gases. The scarceness of relevant study, as well as the sensitivity of the topic, were the major motivations behind the intention to present these notes for publication. A timeline of the detonation phenomenon and its physical comprehension was drawn to justify the unsuitability of the continuum hypothesis of describing gaseous detonations. Then, the theory behind the Boltzmann equation and DSMC is elaborated. Finally, a discussion of the available study on the topic is introduced and concluded.

Review of "The Detonation Phenomenon"

Review of "The Detonation Phenomenon"

Professor John H. S. Lee: The Detonation Phenomenon

The book “The Detonation Phenomenon” by Professor John H. S. Lee is intended for engineers and graduate students with backgrounds in thermodynamics and fluid dynamics. It fulfills that mission perfectly. The book is an excellent, thorough review of the basic experimental and theoretical aspects of gas phase detonation. Gas phase detonation has frequently been studied, because its three-dimensional shock wave structure can be photographed, the pressure it produces is not extreme, as opposed to that of a solid or liquid explosive, and the chemical reaction rates that control its propagation can be measured in shock tubes. Professor Lee has assembled a wonderful combination of fantastic photographs from all over the world plus basic theoretical explanations of the various phenomena involved in gas phase detonation. The book has a mechanical engineering slant, emphasizing the structures of shock and detonation waves and their interactions with surrounding materials. The book covers the discovery of detonation with pictures of the scientists who uncovered the basic properties of detonation waves. The first three chapters and part of Chapter 4 contain necessary experimental and theoretical background found in other books, but this information is presented in a very clear concise manner. Each chapter ends with closing remarks, which often contain a list of unsolved problems. The bibliographies at the end of each chapter contain most of the relevant references. The remaining chapters of “The Detonation Phenomena” are unique and brilliantly presented. Chapter 5 is a numerical analysis of unstable detonation that provides an excellent summary of several complex topics. Professor Lee systematically discusses: linear stability analysis; asymptotic modeling; direct computer simulations; and chemical effects on the stability of detonation waves. He ends Chapter 5 with its main message that theory and numerical modeling support that the experimental fact that all detonation waves are unstable and exhibit multi-dimensional wave structures. Chapter 6 is entitled “Unstable Detonations: Experimental Observations.” It begins with the 1926 discovery of “spinning detonation” and presents photographs and explanations of all of the detonation flows discovered thus far. This chapter is by far the best collection of famous photographs from many authors of detonation wave structures. Many cases of multi-headed detonation waves and the triple shock intersection points that control their propagation are illustrated. The effects of various geometries on the “cellular structures” produced by the interactions of these “triple points” are covered more completely than in other books on gaseous detonation. Chapter 6 ends with a basic discussion of how chemical energy release controls detonation wave cell size. Chapter 7 discusses the influence of boundary conditions on gaseous detonation wave propagation. The influences of rough versus smooth walls (turbulent flow) on detonation velocity and cellular structures are important engineering concerns that are covered very well in Chapter 7. An imaginative experiment developed by Professor Lee’s group was to pass a detonation wave over an acoustically absorbing material. When the triple shock intersection points of a detonation waves interacted with this material, the cellular structure of the detonation was destroyed. The detonation wave exited that section of tube as a planar shock wave followed by a deflagration wave. This experiment proved that the cellular structure was essential to gas phase detonation

Reconsideration on the role of the specific heat ratio in Arrhenius law applications

Arrhenius law implicates that only those molecules which possess the internal energy greater than the activation energy E a can react. However, the internal energy will not be proportional to the gas temperature if the specific heat ratio γ and the gas constant R vary during chemical reaction processes. The varying γ may affect significantly the chemical reaction rate calculated with the Arrhenius law under the constant γ assumption, which has been widely accepted in detonation and combustion simulations for many years. In this paper, the roles of variable γ and R in Arrhenius law applications are reconsidered, and their effects on the chemical reaction rate are demonstrated by simulating one-dimensional C-J and two-dimensional cellular detonations. A new overall one-step detonation model with variable γ and R is proposed to improve the Arrhenius law. Numerical experiments demonstrate that this improved Arrhenius law works well in predicting detonation phenomena with the numerical results being in good agreement with experimental data.

Investigation of Jet Formation with Overdriven Detonation in High Density Explosive

To increase largely the performance of shaped charge, it is required to generate detonation velocity much higher than CJ velocity or detonation pressure much higher than CJ pressure of existing high explosives. One solution is the application of overdriven detonation phenomena. In this study, the effects of overdriven detonation in tungsten loaded high density explosive on the performance of shaped charge were demonstrated by experiments and numerical simulation. Sample shaped charge was composed of the inner layer tungsten loaded high density PBX and outer layer high velocity PBX. Concentration of tungsten powder in high density PBX was varied from 20 to 60% in mass. The pressure of overdriven detonation in inner layer PBX was measured by PMMA gauge, and was shown to be higher than 50GPa. The experimental results showed that the initial jet velocity and jet penetration velocity in target plates were largely increased by the effects of the overdriven detonation in tungsten loaded high density PBX.

Parameterization of the porous-material model for sand with different levels of water saturation

The experimental results for the mechanical response of sand (at different levels of saturation with water) under shock-loading conditions generated by researchers at Cavendish [Bragov AM, Lomunov AK, Sergeichev IV, Tsembelis K, Proud WG. The determination of physicomechanical properties of soft soils from medium to high strain rates, November 2005, in preparation; Chapman DJ, Tsembelis K, Proud WG. The behavior of water saturated sand under shock-loading. In: Proceedings of the 2006 SEM annual conference and exposition on experimental and applied mechanics, vol. 2, 2006.p.834–40] are used to parameterize our recently developed material model for sand [Grujicic M, Pandurangan B, Cheeseman B. The effect of degree of saturation of sand on detonation phenomena associated with shallow-buried and ground-laid mines. J Shock Vib 2006;13:41–61]. The model was incorporated into a general-purpose non-linear dynamics simulation program to carry out a number of simulation analyses pertaining to the detonation of a landmine buried in sand and to the interactions of the detonation products, mine fragments and sand ejecta with various targets. A comparison of the computed results with their experimental counterparts revealed a somewhat improved agreement with the experimental results in the case of the present model as compared to the agreement between the widely used porous-material/compaction model for sand and the experiments.

Re-initiation phenomenon of gaseous detonation induced by shock reflection

The two-dimensional, time-dependent, reactive Navier–Stokes equations including the effects of viscosity, thermal conduction and molecular diffusion were solved to reveal the wave evolution and chemical dynamics involved in the re-initiation process. The computation was performed for hydrogen–oxygen–argon mixtures at the low initial pressure (8.00 kPa), using detailed chemical reaction model. The results show that, the decoupled leading shock reflects on the right wall of the vertical branch. High temperature and pressure behind the reflected shock induce the generation of hot spots and local explosion. Therefore, the re-initiation of gaseous detonation occurs. In the re-initiation area, there exist very high OH concentration and no H2 concentration. However, in front of reflected shock, there exist relatively high H2 concentration and no OH radicals. Additionally, the shock–flame interaction induces RM instability. This results in the fast mixing between hot reacted gas mixture and the relatively cold unreacted gas mixture and accelerates the chemical reactions. However, the shock–flame interaction contributes much less to the re-initiation, in contrast with shock reflection. The transition of leading shock from regular reflection to Mach reflection happens during the re-initiation. The computed evolution of wave structures involved in the re-initiation is qualitatively agreeable with that from the experimental schlieren images.

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.