Multi-spot modes of unsteady gasless combustion of a thick-walled cylinder under adiabatic conditions

Propagation of multi-spot spinning waves in a cylindrical specimen with a coaxial inner channel is studied by numerical methods under the assumption of the absence of heat removal from the outer surface of the specimen and from the channel surface. Variations of the spinning wave characteristics (longitudinal and tangential velocities, “pitch,” and maximum temperature and period) are demonstrated by an example of two-spot spinning waves for specimens of different sizes with a fixed channel radius, for specimens of a particular size with different channel radii, and for specimens with a constant wall thickness and varied inner and outer radii. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 3–14, January–February, 2007.     

Some characteristics of a spin combustion site and of the processes occurring in it

The investigated specimens were made by compression of titanium powder. They were burnt in a nitrogen atmosphere. Channels were detected below the specimen surface burnt in a spin regime. The dimension s of the spin combustion site were estimated, and the nitrogen pressure effect on the site dimensions was determined within the range 100–1800 torr. Data were obtained on the degree of metal nitrating and the phase composition of the layer, traversed by the spin site, and of the other specimen layers as a function of their distance from the surface. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 46–49, May–June 1988.     

Combustion of pressed specimens of heterogeneous systems subjected to a constant axial mechanical load

The growth dynamics of the height of burning pressed specimens with the specimen ends subjected to a compressive force of constant magnitude is studied using the heterogeneous Ti+C+20% TiC system as an example. It is found that in the examined range of compressive forces 0.1–2 kg/cm², the growth of the height of the burning specimens with time obeys a linear law; under a compressive force of ≈0.1 kg/cm², the specimen height increases by ≈100%, and under a force of ≈2 kg/cm², it increases by about 25%. The method used to measure the growth dynamics of the specimen height during combustion proved a useful tool for the experimental determination of both the burning time of the specimens and the delay in the transfer of combustion through an obstacle. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 103–109, May–June, 2007.     

Effect of macroscopic heterogeneity of the medium on the solid-state combustion wave characteristics in thermally and chemically heterogeneous media

A macroscopically heterogeneous medium is modeled by a set of cylinders (rods) pressed from a mixture of solid reagents, which have coaxial cylindrical cores made from an inert material. A three-dimensional mathematical model describing propagation of combustion waves over one cylinder is studied by numerical methods. The influence of the distance between the centerlines of the neighboring cylinders and transverse sizes of the cylinders on characteristics of combustion waves propagating over a heterogeneous medium is considered. It is demonstrated that there exists an optimal distance between the inert rods, which ensures a much higher velocity of the combustion wave along the specimen than the theoretically predicted velocity of the classical combustion wave propagating over a solid specimen. New types of spinning waves are described, whose motion makes the high-temperature spot move inside the charge mixture. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 39–49, May–June, 2008.     

Mathematical model of continuous detonation in an annular combustor with a supersonic flow velocity

A two-dimensional unsteady mathematical model of a continuous spinning detonation wave in a supersonic incoming flow in an annular combustor is formulated. The wave dynamics in a combustor filled by a gaseous hydrogen-oxygen mixture is studied. The possibility of continuous spin detonation with a supersonic flow velocity at the diffuser entrance is demonstrated numerically for the first time; the structure of transverse detonation waves and the range of their existence depending on the Mach number are studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 6, pp. 83–91, November–December, 2008.     

Wet spinning of acrylic microfibres

Polyacrylonitrile microfibres with a linear density of 0.02–0.10 tex can be manufactured by wet spinning into spinning baths with a low concentration of precipitant. When the jets of spinning solution come into contact with such a spinning bath, a concentration of precipitant lower than the threshold concentration where coagulation does not take place is established on the surface of the fibre for a short time (0.02–0.56 sec). The spun fibres have a liquid segment longer than the stressed part of the jet exposed to normal stresses. Fibres with a liquid segment can be drawn by 5–10 times, which allows fabricating microfibres with a linear density of 0.02–0.10 tex having a strength of 45–80 cN/tex and elongation of 15–20%. Fibres spun into baths with a low concentration of precipitant have high porosity, which could be attributed to formation of a liquid polymer phase in phase decomposition of the spinning solution. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 3, pp. 16–20, May–June, 2000     

Gas detonation in a channel with transverse ribs

Results of experiments on detonation propagation in a rectangular horizontal channel with high ribs on the lower wall are presented. The experiments were performed with acetylene-oxygen mixtures. An interval of initial pressures is found, in which low-velocity detonation with a steady velocity of 0.38–0.55 of the Chapman-Jouguet velocity without losses exists. This detonation wave is a system consisting of a shock wave and a flame. Owing to gas outflow to the layer occupied by the ribs, the flame is maintained at a constant distance from the shock wave, which is approximately equal to the free transverse size of the channel. This distance weakly decreases with increasing initial pressure and is almost independent of the burning rate of the gas at standard temperature. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 82–86, September–October, 2007.     

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     

Measurement of the impurity gas pressure during combustion of a “gasless” system in a long cylindrical shell

A method for estimating the maximum impurity gas pressure averaged over the specimen cross section in the combustion wave for different cross sections of a long specimen is proposed. The impurity gas pressure in a given specimen cross section is understood as the gas pressure that induces cross-sectional fracture of the specimen enclosed into a shell and certain displacement along the shell of the pressed matter portion located ahead of the combustion wave front at the instant of fracture initiation. Special composite specimens are used to ensure constant conditions of impurity gas removal from the volume and to model the SHS process and associated impurity degassing in the case of long (L/d γ 1) cylindrical specimens under the condition L = const. The model mixtures are chosen to be typical compositions for SHS: Ti+C and Ti + 2B.     

Study of spinning of polyacrylonitrile fibre with a mathematical model

With an adequate mathematical model, it is possible to study the effect of the most important technological parameters on the fibre formation process and to optimize it with consideration of the equipment, spinning conditions, and linear density of the fibre. The promise of regulating the spinning process by addition of a precipitator to the spinning solution was demonstrated. Translated from Khimicheskie Volokna, No. 2, pp. 51–53, March–April, 1998.     

Spinning disk mechanism of a machine for spinning aramid fibres

Altering the design of the spinning disk mechanism used in spinning aramid fibres will increase the lifetime of the mechanisms and the quality of the spun fibres. Translated from Khimicheskie Volokna, No. 5, pp. 55–56, September–October, 2008.     

Characteristics of HMX combustion waves at various pressures and initial temperatures

Temperature profiles and combustion-wave parameters are obtained experimentally for combustion of pressed HMX at room temperature and pressures of 1–500 atm and in the case of a change in the initial temperature of the specimens from −170 to +100°C at pressures of 1–75 (90) atm. The following combustion-zone parameters are determined: the heat effect in the c-phase, the heat transfer from the gas to the c-phase by thermal conduction and radiation, the rate of heat release in the gas near the surface, and the dimensions and temperature of the combustion zones. The authorsé previous conclusion that there is one process of decomposition and evaporation of HMX during its gasification in the condensed-phase reaction layer of the combustion wave is confirmed. Dependences of the fraction of decomposed HMX on the initial temperature of the specimens and the pressure are obtained. The differential characteristics of the combustion rate, surface temperature, and radiative heat transfer, required for the nonlinear theory of HMX combustion stability, are evaluated. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 59–66, March–April, 1998.     

Rheological properties of liquid-crystalline solutions of poly(p-phenylene terephthalamide) and behavior of the jet in spinning through an air space

LC solutions of PPTA behave like liquids with a power law of flow and n =0.65–0.78 for flow through the channels of standard spinnerets with small diameters and q =0.88–0.95 for longitudinal flow in jets. Spinneret expansion of a freely falling jet in channels with small diameters is equal to 1.70–1.75 and is not a function of the shear rate on the wall. Spinneret expansion is preserved in conditions of repeated drawing of the jets in the air space until very small air spaces at 1.5–2.5 mm are used. In spinning PPTA fibres through an air space with a high jet draw ratio, only a small fraction of this drawing in the spinning bath is possible. Translated from Khimicheskie Volokna, No. 2, pp. 3–7, March–April, 1997.     

Critical conditions of the combustion of compressed titanium specimen

Critical combustion conditions were investigated for compressed titanium specimens concerning the specimen density and the oxygen concentration in a O₂−Ar mixture. It was shown that there is a minimum specimen density at which combustion characteristics undergo a significant change. The completeness of combustion monotonically decreases with increase in density. Possible causes of the observed phenomena are considered. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 50–55, May–June 1998.     

Experimental studies of the ignition of a solid propellant in water

The ignition of a solid propellant in water by means of an unsealed system of ignition in the form of an open channel with a heating coil placed in the channel is considered. The ignition system operates according to the principle of creation of extreme conditions of water boiling in the channel with heat supply from an electrical heater. It was established visually that the heating of the walls is preceded by a preliminary period connected with the change in the state of aggregation of water. The system was tested on solid-propellant specimens. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 52–57, July–August 1999.     

Numerical simulation of the influence of tube diameter on detonation regime and structure in mixtures with two-step energy release and double cellular structure

We present the results of a numerical study of the detonation structure in a reactive mixture whose chemical energy is released in two steps of very different characteristic times. Detonation in these mixtures exhibits a double detonation cellular structure. By decreasing the detonation tube diameter, several detonation structures are successively obtained: a multiheaded double cellular structure, a double cellular structure with a spinning mode of the transverse wave of the second exothermic step, a single cellular structure, and a spinning mode of the transverse wave of the first step. This is the first three-dimensional numerical investigation of such mixtures. Although a lack of resolution does not allow a resolution of the fine structure at the beginning of the large detonation cells, the results agree qualitatively with experiments. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 101–108, July–August, 2009.     

Reflection of a shock wave in a dusty cloud

The problem of shock-wave passage along a cloud of particles adjacent to a solid surface is studied numerically and analytically. The wave pattern of the flow near the shock wave reflected from this surface is analyzed within the framework of the equilibrium approximation of mechanics of heterogeneous media. The conditions of the transition from regular to irregular reflection from the substrate of the refracted shock wave inside the cloud are obtained analytically. The results of numerical simulations of a nonequilibrium flow in the two-velocity two-temperature approximation are compared with data obtained in the equilibrium approximation. Nonequilibrium and equilibrium flows are found to become more similar as the particle size decreases. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 121–131, January–February, 2007.     

Detonation of a mixture of RDX particles partially filling a cylindrical channel

Using a mathematical model of a two-phase, two-velocity medium, detonation in an annular layer of a suspension of volatile secondary explosives adjacent to the wall of a cylindrical channel is numerically investigated. The dynamics of formation and the special features of the structures of a two-dimensional reaction zone of a detonation wave in a gas mixture of RDX particles are discussed. A detonation regime with a vortex structure of the reaction zone is obtained in calculations for the first time. The geometrical limits of detonation in a channel are determined. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 4, pp. 79–87, July–August 1999.     

Real-time control of solid-propellant combustion by a catalytic method

Principles of contact catalysis of combustion are described. The essence of this process implies that a block catalyst contacting the surface of the burning propellant specimen increases the burning rate and allows controlling combustion at a temperature of 400 to 600°C with formation of a large volume of versatile gaseous products, i.e., is the basis for creating low-temperatures gas generators. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 86–91, January–February, 2007.     

Heat resistance of alumina ceramics

A method for evaluating the heat resistance of structural ceramics according to which the thermally stressed state is created by blowing a directed air flow into the tip of a notch in a heated prismatic specimen is presented. For this purpose a special complexly shaped notch is formed in order to provide free inflow of the air to its tip. The radius of curvature of the notch in alumina ceramics is 5 Μm. In blowing, the heat is removed predominantly from a local volume at the tip of the notch, thus providing a “local” thermal shock. The heat resistance of alumina ceramics obtained by sintering and reaction bonding is studied. The mechanical properties of Al₂O₃ tend to improve after a local thermal shock. The tendency is proved by testing a statistically reliable sample of unnotched specimens by the conventional method for determining the heat resistance. This tendency can be explained by “curing” of some of the defects (commensurable with the elements of the substructure) in densely sintered ceramics under the effect of thermal stresses. This was established due to the low scattering of the values of the mechanical properties measured in testing a sample of specimens with a special notch. It cannot be detected in tests of unnotched specimens within the same sample. A heat cycle of “850‡C-water” worsens the mechanical properties of notched and unnotched specimens due to the initiated microfracture. Translated from Ogneupory i Tekhnicheskaya Keramika, Nos. 1–2, pp. 14–19, January–February, 1999.