Electrical effects in propellant compositions radiated by electrons

Radiation-induced electrical conductivity of composite and ballistite solid propellants under pulsed (2.5 · 10⁻⁶ sec) and continuous (1–100 sec) radiation by a flux of fast electrons is studied. Conditions for the development of an electrical breakdown during electron radiation are determined, and the relation between this phenomenon and the composition of the composite propellant is considered. For the ballistite propellant, radiation-induced conductivity is studied both in the highly elastic and in the vitreous state. Based on experimental results, the parameters of a semi-empirical model of radiation-induced conductivity are determined for both types of propellants. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 52–63, September–October, 2007.     

Determining the unsteady combustion behavior of propellants from results of closed-bomb testing

Two methods for processing the results of closed-bomb tests of propellants are proposed: a method for determining the force of propellant, the covolume of propellant gas, and the pressure dependence of the degree of propellant combustion that takes into account the heat exchange between the combustion products and the walls of the closed bomb; a procedure for determining the linear behavior of unsteady combustion in the form justified by Ya. B. Zel’dovich. It is shown that accounting for heat losses is necessary not only to determine the force of propellant and the covolume of propellant gas but also to determine the combustion behavior. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 29–38, March–April, 2006.     

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.     

Model of Vapor—Air Gasification of a Solid Fuel in a Filtration Mode

A two-temperature mathematical model of steady filtration combustion of a solid fuel in open systems is proposed. Air or a mixture of air with water vapors is considered as a gaseous oxidizer. The model takes into account that the heat capacities of the phases depend on temperature and composition and that the reactor length is finite and allows obtaining the composition of gaseous combustion products. Calculated results on gasification of a mixture of carbon with an inert component are presented. It is demonstrated that thermodynamic calculations are important for obtaining the upper estimate of gasification efficiency. Even a sufficiently long reactor becomes “short” in the regime of transient combustion waves, which results in more intense entrainment of heat by combustion products and, as a consequence, in lower efficiency of the process. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 65–72, January–February, 2006.     

Model for the propagation of a stationary reaction front in a viscoelastic medium

A coupled thermomechanical model for the propagation of a stationary chemical-reaction wave in a condensed medium is developed. Stresses and strains that arise during the reaction as a result of thermal and “concentration” expansion of the material are related by Maxwell’s equations for a viscoelastic medium. The expression for the heat flux is written as a generalized Fourier law with finite relaxation time for the heat flux. It is shown that deformation of the material in the reaction zone can lead to an apparent change in the activation energy, heat effect, and other characteristics of the system. This model allows for the existence of two different — subsonic and supersonic — regimes of propagation of the front, as well as the model in which the stress- and strain-tensor components are related by a generalized Hooke’s law. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4. pp. 41–51, July–August, 2000.     

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.     

On the threshold nature of erosive burning

A physical explanation for the existence of the threshold of erosive burning is proposed. It is shown that this type of combustion occurs when the thickness of the laminar sublayer in the turbulent boundary layer becomes smaller than the thickness of the laminar combustion zone. In this case, turbulent flame in the gas phase is formed. Relations are obtained linking the critical (threshold) velocity of the blowing flow and the critical Vilyunov number to the properties of the propellant and the gas resulting from propellant decomposition. Simple exponential dependences on the blowing velocity are found for the burning rate. The simplest representation of the erosive burning rate is obtained using the Bulgakov-Lipanov number, whose threshold value is equal to unity. A new mechanism for the occurrence of negative erosion is proposed, according to which the burning rate decreases during blowing because the boundary layer is displaced, resulting in a decrease in the heat flux from the flame zone to the solid-phase decomposition surface. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 61–71, May–June, 2008.     

Mechanism of catalysis in combustion waves of modern ballistite propellants

The effect of 12 catalysts that contain iron, lead, and nickel oxides, cobalt, potassium, copper, sulfur, and lead compounds, and soot additives on the structure and parameters of the combustion-wave zones for nitramine-containing ballistite propellant at pressures of 20, 50, and 100 atm is studied by a thermocouple technique. The many-parameter conversion of combustion waves by the catalysts is described in the form of matrixes of changes of the main combustion-zone parameters introduced by the catalyst. The zones in which these catalysts act are shown, and the magnitudes of the action are found. The resulting zone parameters make it possible to separate four regimes of catalytic action in the combustion wave: normal, blowing-off, compensation, and gas-phase. It is found that the significant increase in the combustion rate is generally caused by the increase in subsurface heat release in the c-phase and heat release on the burning surface. The reactivity series of these catalysts is given. It is shown that the combustion-wave parameters for catalyzed nitramine-containing ballistite propellants can obey unified laws. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 75–85, September–October 1999.     

On the ignition of a layer of combustible forest materials by light radiation

The ignition of a layer of combustible forest materials by luminous radiation was studied experimentally. The minimum radiant heat flux densities required to ignite combustible forest materials are determined for a neodymium-doped glass laser and a tungsten lamp. It is established that the heat flux, density increases with increase in the moisture content and density of the layer of combustible forest materials and decreases with increase in the diameter of the light spot, and the critical flux density is higher for the laser radiation than for the incandescent lamp. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 22–25, November–December 1999.     

Mechanism and laws of combustion of composite solid propellants with a coolant

The model of combustion of a composition consisting of a quasi-homogeneous composite propellant (matrix) and coolant particles is considered. The model is based on the leading role of exothermal decomposition of the matrix and on the cooling effect of the second component by virtue of transverse heat transfer between the components in the condensed and gas phases. Formulas for combustion characteristics (temperature, burning rate, its sensitivity to pressure, and initial temperature) are derived and analyzed. The calculated dependences of these characteristics on pressure, particle size, concentration, and thermal effects of decomposition of the components show that transitional regimes with a stronger dependence of the burning rate on pressure than that of the initial propellant are reached in a certain range of parameters. An algorithm is proposed, and a parametric identification of the model on the basis of experimental data is performed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 51–60, November–December, 2007.     

HMX flame structure for combustion in air at a pressure of 1 atm

The chemical structure of HMX flame during combustion in air at a pressure of 1 atm was calculated using molecular beam mass spectrometric sampling. HMX vapor was recorded for the first time near the burning surface. A total of 11 species were identified in the HMX flame (H₂, H₂O, HCN, N₂, CO, CH₂O, NO, N₂O, CO₂, NO₂, and HMX vapor), and their concentration profiles were measured. The HMX combustion was unstable. The species concentration profiles exhibit periodic pulsations related to variation in the HMX burning rate. The HMX flame structure at various distances to the burning surface was determined using the average value of the burning rate. Two main zones of chemical reactions in the flame were found. In the first zone ≈0.8 mm wide adjacent to the burning surface, HMX vapor decomposes and NO₂, N₂O, and CH₂O react with each other to form HCN and NO. In the second zone ≈0.8–1.5 mm wide, HCN was oxidized by nitric oxide to form the final combustion products. The composition of the final combustion products was analyzed. The global reaction of HMX gasification at a pressure of 1 atm was established. Heat release values in the condensed phase calculated by the global gasification reaction and by the equation of heat balance on the burning surface (using literature data from microthermocouple measurements) were analyzed and compared. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 6, pp. 26–43, November–December, 2008.     

Approximate method for solving problems of ignition theory

A method is proposed to determine the moment of ignition of a semi-infinite massif of a condensed material exposed to an external heat flux specified as an arbitrary function of time. The method uses the fractional-differentiation formalism. For large values of the heat flux, the calculation results coincide with the results obtained using well-known methods. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 23–28, March–April, 2006.     

Hydrodynamic molding method — a tool of resource-saving technology in ceramic and refractory production

A concept of ceramic refractory technology is formed, based on advanced examples of material nano-, micro-and macrotechnology, of the technique of high and elevated pressure (0.1–1.0 GPa), high-speed (pulsed, 5–15 msec) loading and molding of powder heterocompositions in hydrodynamic machines of the HDM class, performed under the action of propellant explosive substances (ES), manufactured from inexpensive artillery powders. Control of dynamic and production parameters for molding objects is provided by the weight of ES charge or the charging density in the hydrodynamic machine (HDM) combustion chamber. Scientific and technical bases created in GNU IPM NAN Belorussii for ceramic and refractory technology based on high energy pulsed compaction make it possible to organize and assimilate output of a broad range of objects for the ceramic and refractory industries. Translated from Novye Ogneupory, No. 7, pp. 48–49, July 2008.     

Oxidation of a coal particle in flow of a supercritical aqueous fluid

A study was made of the conversion of single spherical coal particles of diameter 1–5 mm in a supercritical H₂O/O₂ fluid with an oxygen mass fraction of 0–6.6% in a semibatch reactor at a pressure of 30 MPa and a temperature of 673–1023 K. A decrease in the particle mass was observed in two parallel processes: gasification of coal with water and oxidation of coal with oxygen. An activation energy 19 ± 7 kJ/mole and a pre-exponential factor 10^−2±0.4 sec⁻¹ were obtained under the assumption of zero order for the concentration H₂O and an Arrhenius dependence for the rate of gasification with water. The oxidation with oxygen at a temperature above 780 K was found to be limited by the rate of O₂ diffusion to the coal organic matter. Below 780 K, the rate of heterogeneous oxidation with oxygen is described by a first-order reaction for the concentration of O₂ and a zero-order reaction for the concentration of H₂O with an activation energy of 150 ± 27 kJ/mole and a pre-exponential factor of 10^7.6±1.9 cm³/(g · sec). __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 23–31, March–April, 2008.     

Study of solid propellant ignition by a hot gas stream

The process of fast ignition of double-base solid propellants (ignition time 0.6–40 msec) is studied in a model rocket chamber by means of fine thermocouples that are located on the surface being ignited and in the igniting gas stream under rapidly varying external conditions. The basic parameters of the process (propellant surface temperature, gas-propellant heat transfer coefficient, heat flux from the gas to the propellant, and the heat content and the heat release in the propellant) are obtained as functions of time. Three ignition regimes are found: fast, normal, and delayed. We discuss briefly the nature of the transition to steady-state combustion for the obtained regimes. The directions of future studies are noted.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 20–26, May–June, 1993.     

CO2 gasification of Thai coal chars: Kinetics and reactivity studies

Two sized fractions (<75 μm and 150–250 μm) of Ban Pu lignite A and Lampang subbituminous B coals were pyrolyzed in a drop tube fixed bed reactor under nitrogen atmosphere at 500–900 °C. Gasification of coal chars with excess carbon dioxide was then performed at 900–1,100 °C. The result was analyzed in terms of reactivity index, reaction rate and activation energy. It was found that chars at lower pyrolysis temperature had highest carbon conversion, and for chars of the same sized fraction and at the same pyrolysis temperature, reactivity indices increased with gasification temperature. The lower rank Ban Pu lignite A had higher R _s values than higher rank Lampang subbituminous B coals. Smaller chars from both coals had higher R _s values, due to the higher ash content. At present, it can be concluded that, within the gasification temperature range studied, gasification rates of chars obtained at various pyrolysis temperatures showed a linear correlation with temperature. However, additional experiment is needed to verify the correlation.     

Regimes of gas combustion in a porous body of a cylindrical heat generator

A stationary model of filtration combustion of a gas with allowance for conditions at the entrance to the porous body and conditions of heat exchange with the gas phase surrounding the burner and with the heat exchanger is proposed and numerically analyzed. Ranges of parameters where the regime of gas combustion with a narrow reaction zone near the outer surface of the porous body are determined. Mechanical stresses arising in the porous body owing to high temperature gradients and gas pressure in the pores are estimated. The rate of gas combustion and the radiative heat flux from the burner surface are plotted as functions of process-dependent parameters. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 1, pp. 18–29, January–February, 2009.     

Erosive burning of a solid propellant in a supersonic flow

We present results of an experimental study of burning of a ballistite solid propellant (gun powder H) in a supersonic flow. It is shown that the criterial dependence of the erosion coefficient on the Vilyunov parameter obtained on the basis of experimental results in a subsonic and a supersonic flow describes satisfactorily experimental data for a supersonic flow in the examined range of Mach numbers M=1–2.8 as well. A more correct approximation formula for the range of parameters considered is derived. The specific features of the flow along the surface of a solid propellant at M>1 is analyzed, and this analysis has revealed some problems in the interpretation of experimental data. Translated fromFizika goreniya i Vzryva, Vol. 34, No. 1, pp. 61–64, January–February, 1998.     

Gas combustion in a narrow tube

A simplified model of flame propagation over a single capillary in the low-velocity regime is proposed. The model is based on the concept that the main features of flame propagation in the low-velocity regime are determined by the heat flux along the tube wall from the combustion products to the fresh mixture. Qualitative agreement with experimental results is obtained. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 22–26, March–April, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 99-03-32309).     

Effect of a low-amplitude shock wave with residual pressure on hexagonal boron nitride

We have performed shock-wave loading of hexagonal boron nitride under pressures of10.8–16 GPa in the range of initial temperatures of20–500°C in flat recovery ampoules allowing one to sustain residual pressures of ∼1 GPa. To form a plane shock wave, a gas gun was used. Application of a residual pressure under the action of a shock wave with an intensity of16 GPa increased the yield of wurtzite boron nitride by4 to5 times. This explained on the basis of the assumption of wurtzite formation from the amorphous phase in high-temperature zones of adiabatic shear in the residual regime. Center of High Dynamic Pressures, Mendeleevo 141570. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 5, pp. 122–127, September–October, 1997.