Bubble detonation conditions

Initiation of bubble detonation in the system “inert liquid-explosive gas bubbles” by a detonation wave in a gas was studied experimentally. Compression-wave pressure profiles were determined as functions of the length of the initiation section and the initial pressure of the explosive gas mixture in it. It was shown that because of the effect of the explosive-gas volume between the diaphragm and the upper boundary of the bubble medium, the pressure in front of the initiating wave increased much more slowly than the initial pressure. The optimal length of the initiation section was found, and the critical (minimum) initiation pressure in it and at the shock-wave front were determined. It was found that for a fixed gas volume concentration in the bubble medium, the pressure in the initiation section increased insignificantly as the length of the section decreased. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 84–90, March–April, 2007.     

Transformation of shock waves at the interface of bubble media

The transition of shock waves from a bubble medium into a liquid or into another bubble medium with different properties is considered experimentally. Data on the structure, velocity, and pressure in the shock wave incident onto the interface, transmitted wave, and reflected wave are obtained. Experimental results are compared with numerical data. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 97–104, March–April, 2006.     

Reflection of a bubble-detonation wave from a rigid obstacle

The process of detonation-wave reflection from a rigid obstacle in mono- and polydisperse bubble media is studied experimentally. The evolution of the reflected wave formed upon interaction of the detonation wave with the butt-end of a shock tube is traced. The structure of the detonation and reflected waves is studied and the wave pressures are measured at various parameters of the bubble media. The damping constants of the reflected waves are determined. In addition, the velocities of the detonation and reflected waves are measured. The effect of the gas-bubble size on the characteristics of these waves is investigated. The energy-dissipation mechanisms in the detonation and reflected waves in the bubble media are analyzed qualitatively. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 107–113, May–June, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 98-03-32325).     

Transport equation for gas-dynamic perturbations in a spatially nonuniform self-igniting medium

An approach is developed to describe the formation and propagation of small gas-dynamic perturbations in a spatially nonuniform self-igniting medium for arbitrary chemical-reaction kinetics. An asymptotic equation describing the variation in the amplitude of the gas-dynamic perturbation along the characteristic is derived, and the conditions of its applicability are defined. Zel’dovich’s spontaneous flame wave is shown to be a natural zeroth approximation to the solution of the equations of gas dynamics. A method is proposed to determine the point in space at which a shock wave is formed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 72–80, May–June, 2008.     

Formation of carbon clusters in deflagration and detonation waves in gas mixtures

Numerical and experimental results of studying the formation of carbon clusters due to propagation of deflagration and detonation waves in enriched acetylene-oxygen and acetylene-air mixtures are described. Experiments are performed in tubes of different diameters (including tubes filled by a porous medium) with wide-range variations of the initial pressure and the fuel-to-oxidizer ratio. A large variety of carbon clusters formed in different regimes of burning of the mixture is found. A typical size of condensed carbon particles is 15–100 nm. In the case of detonation in a porous medium, the size of carbon particles is 15–45 nm; in some tests, large individual fullerene-type particles 150, 400, and 950 nm in size are formed. The fraction of condensed carbon in the total amount of carbon in the initial mixture is found to depend on the wave type; detonation is characterized by the minimum “yield” of condensed carbon. The amount of condensed carbon increases with increasing acetylene concentration in the mixture and initial pressure. The size of carbon particles in the case of deflagration is greater than that in the case of detonation. Cooling of reaction products decelerates condensation and interrupts the growth of carbon particles. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 81–94, May–June, 2008.     

The effect of liquid compressibility,heat loss,and the induction period of the chemical reaction on the structure of a bubble-detonation wave

Calculations were performed of the structure of a bubble detonation wave in a chemically reactive gas-liquid medium with bubbles arranged in layers. With the liquid compressibility taken into account, the amplitude of pressure pulsations decreases, and they move to the leading edge. It is shown that the wave profile depends weakly on the method of calculating the induction period of the reactive mixture and method of taking into account heat losses. A comparison is made of the calculated and experimental pressure profiles of the bubble-detonation wave.     

The effect of bubble size on the detonation wave characteristics

Detonation waves in various monodispersed media containing gas bubbles with a specified diameter were investigated experimentally. The investigation centered on the effect of the bubble size on the critical initiation conditions, the structure and on the properties of the detonation waves in bubbly media. Lower and upper bubble diameter limits were detected for the existence of detonation waves. The behavior characteristics of the gas bubbles of various diameters in the detonation wave are explained. M. A. Lavrent'ev Hydrodynamics Institute, Siberian Division, The Russian Academy of Sciences, 630090 Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 5, pp. 83–91, September–October, 1995.     

Bubble detonation in polydisperse media

Detonation waves in polydisperse bubble media have been studied experimentally. Data on the critical initiation conditions and on the structure and properties of detonation waves were obtained. The characteristics of detonation waves in poly- and monodisperse media were compared. The behavior of gas bubbles with various diameters in the detonation wave have been investigated. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 3, pp. 114–119, May–June, 1997.     

Numerical simulation of the structure of two-dimensional gaseous detonation of an H2-O2-Ar mixture

A two-dimensional structure of detonation waves in an 2H₂+O₂+X Ar mixture is numerically studied in a wide range of initial pressures and degrees of dilution. Good qualitative agreement of the numerical results with experimental data is obtained. The effect of the method of initiation (by one or several sites, symmetric or asymmetric) on the steady structure of detonation waves is studied. The changes in the wave structure induced by variation of the channel width are examined. It is shown that the behavior of the two-dimensional wave structure is qualitatively different for mixtures withX=0 andX>0. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 93–103, September–October 1999.     

Detonation of a thin explosive layer in evacuated tubes

Detenation of thin layers of dispersed primary and secondary high explosives (HE) on the outer surface of glass and plastic tubes 0.6–3 mm in diameter was examined at an initial air pressure inside the tube of 0.1 MPa to 30 Pa. It is shown that, under these conditions, the air practically does not influence the detonation velocity, which for secondary explosives (PETN, RDX, and HMX), is lower than or approximately equal to the Chapman-Jouguet detonation velocityD _CJ for a homogeneous mixture of the same substances. Experiments with a primary HE (lead azide) revealed regimes with a wave velocity higher thanD _CJ and a varying reaction zone pattern. When tubes containing a layer of a secondary HE were filled with an explosive gas mixture, waves of a hybrid detonation with a velocity both higher and lower than that in the evacuated tubes was observed. In tubes with diameter 2–3 mm, detonation proceeded in a spinning regime over the entire range of the initial pressure and at a velocity higher thanD _CJ. It is concluded that in the evacuated tubes with a thin HE layer on the walls, ignition is transferred by the stream of hot detonation products moving at the head of the detonation wave. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 56–67, November–December 1998     

Low-velocity detonation limits of gaseous mixtures

Low-velocity detonation regimes in acetylene-oxygen mixtures are studied experimentally. Data are obtained on the kinematics of detonation waves and on the boundaries of the high-velocity, galloping, and low-velocity detonation regions. In lean mixtures, the lower pressure limit for the detonation regimes in narrow channels is found to be an order of magnitude lower than assumed previously under the assumption that the limiting detonation is always spin detonation. The major structural characteristics of low-velocity detonations are calculated. The boundary between low-velocity and galloping detonation is found to correspond almost exactly to equality between the induction time in a particle and the time for it to move from shock wave to flame. Nearly harmonic oscillations of the flame are observed with periods that are related to the longitudinal size of low-velocity detonation waves. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 89–96, May–June 1999.     

Relation between the critical detonation diameter of explosive charges with characteristics of their shock-wave sensitivity

Correlation dependences between the critical diameter of high explosive (HE) charges and characteristics of their shock-wave sensitivity are theoretically justified. Relations for the critical radius of curvature of the detonation-wave front and for the critical detonation diameter are derived on the basis of the author’s theory of the critical diameter and the generalized kinetic characteristic of HE decomposition determined from the experimental dependence of the distance of transition of the initiating shock wave to the detonation wave on the wave amplitude. A qualitative analysis of these relations reveals good agreement with available experimental data. Key words: detonation, critical diameter, sensitivity, shock-wave initiation of detonation, HE decomposition kinetics. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 101–105, May–June, 2009.     

Steady Detonation in a Bubbly Medium

It is shown that the Iordanskii–Kogarko model contains a steady-state solution for a detonation wave in chemically active bubbly media under the following minimum requirements to the model: compressibility of the liquid and allowance for acoustic losses. The rule for choosing the velocity is formulated. The wave structure of the reaction zone and the velocity of steady bubble detonation are calculated. Key words: detonation, bubbly liquid, reacting gas bubbles, acoustic losses, soliton, solitary wave.     

Effect of the degree of dispersion on the detonation wave structure in pressed TNETB

A VISAR interferometer was used to study the reaction zone in steady-state detonation waves in pressed TNETB at different initial densities (1.23–1.71 g/cm³) and degrees of dispersion (5 and 80 μm) of the initial powdered high explosive (HE). The initial density range in which a pressure rise was observed instead of the theoretically predicted chemical spike is shown to depend on the degree of dispersion of the HE. The unusual change in the parameters in the reaction zone is explained by the heterogeneous structure of pressed HEs, whose decomposition has a local nature and proceeds partially at the compression wave front. A technique for recording wave profiles using LiF windows was developed, which confirmed that all qualitative features observed when using aluminum foils ≈200 μm thick and a water window reliably reflect the detonation wave structure. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 90–95, September–October, 2007.     

Detonation waves in polydisperse bubble media

Detonation waves in polydisperse and monodisperse bubble media are studied experimentally. The data on the critical initiation conditions and the structure and properties of detonation waves are obtained. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 6, pp. 71–76, November–December 1998.     

Critical conditions for initiation of cylindrical multifront detonation

A quantitative relation between the characteristic scales determining the excitation and propagation of cylindrical and spherical detonation waves is found with the use of a technique for diffraction reinitiation of multifront detonation. The effect of the channel depth on the reinitiation conditions is studied. The ideal character (the smallness of losses) of a cylindrical multifront wave is estimated, and this estimate is found to be in agreement with experimental data. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 114–120, March–April, 1998.     

Nonclassical steady-state detonation regimes in pressed TNETB

The reaction zones and the dependence of the velocity of steady-state detonation waves on the initial density of pressed TNETB are studied using a VISAR interferometer. It is shown that, in the range of initial densities of TNETB 1.56–1.77 g/cm³, the propagation of a steady-state detonation wave is possible without the range of elevated pressures (chemical spike) in the reaction zone predicted by the classical theory. The dependence of the detonation velocity on the initial density shows singularities which indicate that a steady-state underdriven regime can occur in this range of initial densities. Based on the well-known theoretical concepts of the hot-spot decomposition mechanism of heterogeneous explosives, it is shown that the possibility of the existence of a steady-state detonation wave without a chemical spike, in particular, underdriven detonation, and the effect of the internal structure of the charge on the detonation regime are explained by the decomposition of explosives at the shock-wave front. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 97–103, November–December, 2007.     

Dynamics of a single bubble with a chemically active gas

It is shown that during adiabatic compression of a gas, because of an increase in the relative number of elementary cells (the characteristic scale of the detonation process), a detonation regime can occur in the microvolume of a bubble. In this case, in view of the sharp decrease in the critical energy of initiation, self-initiation of the gas mixture is most likely caused by an adiabatic increase in the temperature. It is shown that the inertial properties of the liquid lead to strong compression of the products of the instantaneous chemical reaction, and this can be regarded as a main mechanism for strengthening of bubble-detonation waves. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 121–124, March–April, 1998     

Continuous spin detonation of hydrogen-oxygen mixtures. 2. Combustor with an expanding annular channel

A comprehensive numerical and experimental study of continuous spin detonation of a hydrogen-oxygen mixture in an annular combustor with the components supplied through injectors is performed. The hydrogen-oxygen mixture is burned in the regime of continuous spin detonation in an annular combustor 4 cm in diameter with subsequent channel expansion. The flow structure is considered for varied flow rates of the components of the mixture and the counterpressure of the ambient medium. The dynamics of the transverse detonation wave is numerically studied in a two-dimensional unsteady gas-dynamic statement of the problem with the geometric parameters of the combustor consistent with experimental ones. Reasonable agreement with experiments is reached in terms of the shape of detonation fronts, detonation velocity, and height of the wave front. The optimal point of channel expansion beginning is chosen, which ensures the maximum specific impulse in the spin detonation regime. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 95–108, May–June, 2008.