Bifurcation of steady combustion regimes and their influence on the onset of high-frequency oscillations in combustion chambers

We theoretically analyze the mechanism for the onset of poorly reproducible high-frequency oscillations which are induced by combustion. We examine a model, which relates this phenomenon to the possible realization of two fundamentally different combustion regimes in the reverse-current zone. In connection with the combustion of two previously unmixed gases, we determine the means of operation of a mixing element, for which there can exist two combustion regimes for the same boundary conditions. These regimes differ essentially in their stability characteristics. The mathematical model takes into account the influence of chemical kinetics and turbulent mixing.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 4, pp. 10–18, July–August, 1992.     

Combustion wave structure in heterogeneous solid propellants

On the basis of describing physicochemical processes in a mixed solid propellant combustion wave, mathematical techniques are suggested for heterogeneous media which make it possible to consider the heterogeneous and gas-phase combustion regimes for individual components in generalized chemical reaction kinetics and to consider their effect on combustion wave velocity. The agglomeration process for Al powder on a hot surface is studied experimentally by high-speed photorecording. A mathematical model is constructed for Al agglomeration in a combustion wave based on agglomeration mechanisms observed in experiments. The dependence of combustion rate on deformation is determined on the basis of an improved method for optical recording of combustion front movement for loaded specimens. The mechanism of the effect of stress on mixed solid propellant combustion rate is connected with activation of chemical bonds of the polymer matrix, which increases its destruction rate. Use of kinetic theory for the durability of polymers made it possible to obtain an analytical equation expressing the dependence of relative combustion rate on measured specimen deformation.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 8–16, May–June, 1993.     

Catalytic Combustion of Methane over Cobalt–Magnesium Oxide Solid Solution Catalysts

A series of cobalt–magnesium oxide solid solution catalysts (CoMgO) have been prepared using urea combustion methods, and characterised by X-ray diffraction (XRD) and laser Raman (LR). The catalytic activities for methane combustion have been tested in a continuous-flow microreactor. The Co content has a significant effect on the activity of the cobalt–magnesium oxide solid solution catalysts. The catalysts containing 5 and 10% Co have the lowest light-off temperature in methane combustion. In the preparation of cobalt–magnesium oxide solid solution catalysts, higher urea to metal ratio favors the formation of the catalysts with smaller crystal particles and leads to a better catalytic performance for methane combustion. Addition of lanthanum nitrate to the solution of Co and Mg nitrate depressed the formation of the cobalt–magnesium oxide solid solution and decreased the activity of the catalysts for methane combustion. The cobalt–magnesium oxide solid solution catalysts are very stable when the calcination or reaction temperature is no more than 900°C. However, the catalytic activity decreases rapidly after high temperature (>1000°C) calcination, possibly due to sintering of the catalyst and thus decrease of the surface area.     

Aspects of making a superconducting yttrium ceramic by self-propagating high-temperature synthesis

Macrokinjetic features are considered for the combustion in oxygen of BaO₂–Cu–Y₂O₃ mixtures, which produces the high-temperature superconductor yttrium barium cuprate YBa₂Cu₃O_7–x. Studies have been made on how the initial temperature affects the combustion temperature and rate, and the critical temperature for self-ignition has been determined. Ultrasonic activation of the initial powders has an advantageous effect on the product quality. Thermal analysis has been applied to the activated mixtures, which indicates the reason for the rise in burning wave propagation rate and increase in conversion to the superconducting phase.Chernogolovka. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 2, pp. 62–67, March–April, 1993.     

Fracture of solids by weak blasts

In this work, the results of different experiments on blasting rocks and model materials during combustion of powders, combustion and detonation of gas mixtures, and also in explosion of condensed HE charges in inert shells are generalized. Mechanisms of crack incipiency and conditions of crack propagation were determined and factors responsible for the increase in number of cracks with increasing load rate of chamber walls were elucidated. It is noted that the shape of initial cracks and the height of the loading zone of a cylindrical cavity have an effect on the fracture pattern. The kinetics of cracks in camouflet gas combustion is estimated. Attention is paid to the possibility of peripheral destruction of the crack edges in the intracrack gas detonation. Critical fracture surfaces are obtained for radial and disk-shaped cracks under quasistatic and dynamic loading of polymethylmethacrylate (PMMA).Institute of Geophysics, National Academy of Sciences, Ukraine, Kiev 252054. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 4, pp. 100–108, July–August 1995.     

Thermal analysis of hexogen combustion

Experimental data on the combustion velocity of hexogen [RDX, triethylene trinitramine] at various initial temperatures were analyzed considering the temperature-dependence of the density, the heat capacity and the solid-phase reaction kinetics; it is shown that the critical temperature, like the ignition temperature, is the boïling point. Analytic functions were obtained that reproduce the experimental data on the hexogen combustion velocity, the pressure and temperature coefficients of the mass combustion velocity, the derivative of the pressure coefficient with respect to temperature, and the derivative of the temperature coefficient with respect to pressure in the range of 0.098-4.9 MPa and initial temperatures of 293–453 K.Scientific Research Institute of Applied Chemistry, 141300 Zagorsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 3, pp. 20–28, May–June 1994.     

Combustion of aluminum-based mixtures

The enthalpy approach was used to analyze experimental data on the burning rate of various aluminum-based systems. The thermal parameters of the combustion wave have been determined for these systems. It has been established that the temperature of ignition of these systems in a steady-state combustion wave is close to the melting point of aluminum.Scientific-Research Institute of Applied Chemistry, Sergiev Posad 141300. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 6, pp. 71–75, November–December, 1994.     

Comparison of different methods of modeling turbulent combustion in a boundary layer

Three methods of modeling a chemical reaction in the combustion of ethanol injected into the boundary layer through a porous plate are compared. In calculations of the average velocity and temperature and also heat-transfer coefficients, simple models of combustion are shown to be close in accuracy to a model that takes into complete account the kinetics of all reactions occurring during combustion. Simple models fail to determine the composition of reaction products, and it is necessary to take into account the formation rate of each substance entrained in combustion.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 4, pp. 37–42, July–August, 1996.     

Combustion of Mechanically Activated Heterogeneous Systems

A mathematical model for the combustion of preliminary activated heterogeneous systems is proposed which includes equations describing heat conduction, chemical kinetics, and the dynamics of the excess energy accumulated in condensed reagents at the stage of preliminary mechanical treatment. The excess energy decreases as a result of structure normalization and chemical transformation, whose activation energy, in turn, depends on the excess energy in the condensed reagents. The case of stationary combustion is analyzed in detail. The effect of mechanical activation on the velocity of the synthesis wave and its structure is analyzed by numerical modeling. The main conclusions are compared with available experimental data.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 3, pp. 90–97, May–June, 2005.     

Abnormal combustion of long powder tubes in a rocket chamber

The limit of the steady combustion of powder charges of different lengths has been studied in a model combustion chamber of a solid-propellant motor. The value of the critical apparatus constant at which powder extinction occurs was determined. Combustion regimes in which the chamber pressure can be much lower than that in the steady combustion regime were recorded for long charges. The causes of occurrence of these combustion regimes are discussed.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 6, pp. 90–95, November–December, 1996.     

The effect of density on the limits and regularities of spin combustion of titanium in nitrogen

A region of spin combustion in the coordinate system nitrogen-pressure (100–1800 torr)-burning sample-density (2.0–3.3 g/cm ³) has been determined experimentally. The effect of density on the spin combustion characteristics (velocity, frequency, and step) has been studied at various nitrogen pressures. A transition of the spin mode of combustion to stationary with decreasing burning velocity has been observed for the first time.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 1, pp. 53–57, January–February, 1996.     

Directed self-propagating high-temperature synthesis of a series of explosion-emissive metalloceramic materials

The problem of production of materials for electron emitters with specified characteristics using the method of self-propagating high-temperature synthesis has been examined. The conditions under which this process occurs in a reagent mixture containing components that interact by two scheme have been analyzed by thermodynamic calculations of adiabatic temperature. Some laws of combustion have been studied experimentally. A satisfactory agreement has been reached between the experimental and calculated data. The possibility of producing materials with a reinforcing frame has been considered.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 1, pp. 58–65, January–February, 1996.     

Unsteady combustion of a binary gasless mixture ignited by a hot wall

The effect of phase-transition parameters and chemical conversion kinetics on unsteady combustion of gasless systems with a melting reagent is studied. It is found that the change in the kinetic law and in the chemical reaction rate constant resulting from the emergence of the liquid phase in the system destabilizes the combustion. The mean front velocity in the self-oscillatory mode with an adiabatic burning temperature close to the melting point exceeds the front velocity in the steady-state mode. In this case, the front stability improves with an increase in the rate of heat withdrawal from the system and with a decrease in the burning temperature.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 2, pp. 45–50, March–April, 2005.     

Possible mechanism of nonsteady-state erosion combustion of composite solid propellants

It has been demonstrated that in the combustion of composite solid propellants the instantaneous mass burning rate can depend on variations in the velocity of cross-flow of gases even if in the steady-state regime the combustion is insentitive to cross-flow velocity. A method has been proposed for studying the nonsteady-state erosion combustion in experiments with composite systems.Institute of Chemical Kinetics and Combustion, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 4, pp. 40–43, July–August, 1995.     

Evaluating the capillarity of textile materials from wetting kinetics

Conclusions A complex method has been proposed for evaluating the capillarity of modified fibrous materials.Employing this method is useful in choosing an optimum composition of the solution used in the process of modifying textile materials.Using the proposed method, we have decribed the wetting kinetics of polycaproamide yarns and cotton fabrics which have been modified with salt solutions in water and in benzene; and also the wetting kinetics of yarns and fabrics treated with bleaching solutions.Translated from Khimicheskie Volokna, No. 4, pp. 22–24, July–August, 1988.     

Critical conditions and the induction period for combustion of a metal plate in an immobile oxidizing atmosphere

Conclusions Relationships have been obtained in this work for calculating the induction period (16) and (18) and combustion temperature (23) for a metal plate oxidizing by a parabolic rule.It has been shown that in analyzing the critical condition for combustion of a metal plate it should be considered as thermally thin. Critical combustion conditions (23), in particular temperature, do not depend on metal plate thickness. With a sufficiently high initial temperature (T₀>E/8R) there is initiation of an explosive combustion character.Theory developed in this work has been applied in order to describe combustion not only of monolithic, but also porous plates, and also a layer of metal powder.The authors express their thanks to F. I. Dubovitskii for constant support in the work and to V. P. Volodin for carrying out a number of calculations.Chernogolovka. Translated from Fizika Goreniya i Vzryva, Vol. 22, No. 3, pp. 3–10, May–June, 1986.     

Relation between velocity of propagation of isothermal flame and parameters of CS2+O2 mixtures

Based on a review of four mechanisms for the chemical kinetics in the study of controlled combustion of CS₂+O₂ mixtures, expressions were derived, based on the stoichiometric composition, relating the velocity of propagation of a laminar flame and the temperature and pressure of the mixture. The expressions were in good agreement with the experimental data.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 60–62, November–December, 1991.     

Thermooxidative decomposition of phosphorus and metal-containing polyamide fibres

Conclusions -- The thermooxidative decomposition of phosphorus and metal containing polycaproamide fibres prepared by introducing combustion retarders into the polymer melt has been studied.-- It has been found that the synergistic system MPA-AlO(OH), introduced into PCA, leads to the formation of coke-like residues which have a high resistance to oxidation. The coke-like residues obtained on thermolysis of PCA-DAMPA-AlO(OH) are enriched in phosphorus and nitrogen, which indicates a reaction of the flame-proofer with the degradation products of the PCA.Moscow State Textile Academy. Translated from Khimicheskie Volokna, No. 5, pp. 39–40, September–October, 1992.     

Combustion of a composite solid propellant under conditions of static mechanical tensile stresses

Mechanical stresses have a progressive effect on the combustion characteristics of composite solid propellants. On the basis the kinetic theory for the durability of polymers within their composition the mechanism is studied for the effect of stress-strain state on steady combustion rate. Chemical bonds of the polymer matrix are activated as a result of an applied stress and there is an increase in the rate of their thermal destruction. It is shown that this is an important reason for an increase in combustion rate with uniaxial tension. An analytical equation is obtained which expresses the dependence of combustion rate on the magnitude of a prescribed stress or that measured by experiment.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 4, pp. 20–28, July–August, 1993.     

Low–Frequency Instability of Solid Rocket Motors. Influence of the Mache Effect and Charge Geometry

Nonacoustic (low–frequency) instability of combustion of a solid propellant in a jet motor is considered. A model of unsteady combustion in motors with channel charges is proposed. The model takes into account the change in the temperature distribution in combustion products induced by the change in the gas pressure (Mache effect). The unsteady gas–release rate and the temperature of combustion products are determined on the basis of the Zel'dovich phenomenological approach, taking into account the change in the propellant–surface temperature (Novozhilov model) and the flame temperature (Gostintsev—Sukhanov model). The dependence of the stability limit of the solid rocket motor (SRM) on the charge–channel length and pre–nozzle volume of the motor chamber is determined. It is shown that the Mache effect leads to a significant constriction (by a factor of 1.5 to 2) of the range of stable combustion parameters in the SRM. It is found that an SRM with a channel charge has a narrower range of stability in terms of the Zel'dovich parameter k than an SRM with a butt–end charge and an identical combustion–chamber volume. For channel charges, the stability limit depends mainly on the volume of the pre–nozzle part of the combustion chamber.