Low-temperature combustion of energetic materials in filled polymer systems

In systems filled by inert additives, combustion of cellulose nitrate (CN) proceeds in a flameless low-temperature regime with a low linear burning rate. At a standard temperature, the exponent in the low of CN combustion in ballasted mixtures with inert additives in the pressure range of 0.1 to 10 MPa is several times lower than that of pure cellulose nitrate and amounts to 0.23. The qualitative and quantitative composition of gaseous products of flameless CN conversion is found. It is noted that this composition approximately corresponds to data available in the literature for the products of thermal decomposition of cellulose nitrate at comparatively low temperatures. Based on this fact and on a weak dependence of the CN burning rate on pressure in ballasted systems, the process under these conditions is assumed to be controlled by conversion of the energetic component predominantly in the condensed phase. In the case of a composite consisting of cellulose nitrate, silicon carbide, and polymer binder, for samples 10–25 mm in diameter, armoring exerts practically no effect on combustion parameters. Combustion of the same mixture with smaller diameters of non-armored samples is unstable. The presence of a liner establishes a clearly expressed critical combustion diameter in the examined systems. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 98–102, May–June, 2007.     

Numerical analysis of combustion kinetics for hydrogen—air mixtures with NH3, CH4, and C2H6 additives behind shock waves

The possibility of reducing the concentration of nitrogen oxides and HNO_x-group components with simultaneous shortening of the reaction-zone length during combustion of hydrogen-air mixtures in a supersonic flow behind an oblique shock wave by introducing NH₃, CH₄, and C₂H₆ additives into the mixture is analyzed. A numerical study shows that a small (up to 5%) amount of these additives substantially changes the combustion kinetics behind the shock-wave front, shortens the flame length, and diminishes the NO and NO₂ content in the combustion products. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 31–38, May–June, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 96-02-18377).     

Combustion of kerosene in a supersonic stream

Experiments on the organization of the combustion of kerosene in high-enthalpy supersonic air streams is analyzed. The use of promotor additives, as well as improvements in the atomization process, vaporization, and mixing, do not always facilitate efficient combustion development. The existence of a conversion process is found to have a significant effect on the ignition parameters. The burnup intensity can be ensured by adding hydrogen, and the relative position of the fuel injectors is important in that case. The fundamental role of wave structures in determining the length of the combustion zone in the channel is noted. The integral characteristics of combustion for hydrogen and kerosene are compared. Translated fromFizika Goreniya i Vzryva Vol. 35, No. 3, pp. 35–42, May–June 1999.     

Ignition control of methane fueled homogeneous charge compression ignition engines using additives

Homogeneous charge compression ignition is a new combustion technology that may develop as an alternative to diesel engines with high efficiency and low NO_x and particulate matter emissions. In this paper, the effect of additives such as dimethyl ether (DME), formaldehyde (CH₂O) and hydrogen peroxide (H₂O₂) for the control of ignition in natural-gas HCCI engines have been investigated numerically by adopting a single-zone zero-dimensional model. The chemical kinetic mechanism incorporated the GRI-3.0 mechanism that considers 53 species and 325 reactions together with the DME reaction scheme consisting of 79 species and 351 reactions. To simulate HCCI engine cycles, a variable volume computation has been performed by including a piston motion into the SENKIN code at a fixed equivalence ratio of 0.3 and initial mixture pressure of 1.5 bar. It was found that an additive-free mixture did not ignite for the intake temperature of 400 K. A mixture containing a small quantity of additives at the same temperature was ignited. For a fixed quantity of additive, it was found that H₂O₂ addition was effective in advancing the ignition timing as compared to the other two additives. It was found that the percentage of additives required to achieve a near TDC ignition timing increases linearly with the increase in the engine speed while decreases with the increase in the equivalence ratio with the superiority of H₂O₂. Furthermore, the addition of even 7% by volume of H₂O₂ could ignite a mixture at an intake temperature of 350 K, while at least the fractions of 12.5% and 35% by volume were needed for DME and CH₂O, respectively. It was also found that the mass fraction of NO with CH₂O addition was less than that with H₂O₂ addition. At the same time, however, a near TDC ignition timing resulted in a similar amount of NO for both additives. Overall, the enhanced reactivity of CH₄ in the presence of small amounts of additives could be used in HCCI engines fueled with methane to alleviate the high intake temperature requirements.     

Combustion regimes of magnesium in carbon oxides. 1. Combustion in CO2

The oxidation and combustion of solitary magnesium particles in a CO₂ medium in the range of ambient temperatures 898–1323 K are studied experimentally. A regime of slow heterogeneous combustion that separates the regions of slow oxidation and fast vapor-phase combustion is revealed. The relation between the processes of ignition and combustion of a volatile metal and the structure and properties of the surface film is discussed. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 42–49, November–December 1999.     

Self-propagating high-temperature synthesis of porous Ti-Si-Al-C based materials

The pore formation process and the phase composition of the products of combustion of the Ti—Si—Al—C system were studied. The structure of Ti₅(Si,Al)₃C_0.6 single crystals formed in small amounts was determined. The dependences of the burning rate and elongation of the samples on their density and the gas pressure were determined. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 53–60, March–April, 2006.     

Filtration combustion of porous metallic samples in a gas diluted by an inert component

Filtration combustion of a porous layer with natural filtration of the oxidizer diluted by an inert component is studied. The problem of ignition of a porous layer by a heated surface permeable for the gas is solved, and the time of ignition is determined as a function of pressure in the reactor and initial porosity of the sample. Formation of an inert gas “plug” preventing chemical interaction is examined. It is shown that the mean depth of conversion of the condensed reagent in the porous layer depends on the sample length, porosity, pressure of the gas mixture, and concentration of the inert component. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 73–79, January–February, 2008.     

Kinetic mechanism of propane ignition and combustion in air

A detailed kinetic model of propane ignition and combustion in air is developed. The model includes 599 reactions with 92 species and involves both the high-temperature and low-temperature mechanisms of oxidation. The model is tested against experimental data on the ignition delay time, on propane conversion during low-temperature oxidation, on changes in species concentrations during propane pyrolysis, and on laminar flame propagation velocity. The model is tested in wide ranges of the initial temperature T ₀ = 680–1900 K, pressure p ₀ = 0.17–30 atm, and fuel-air equivalence ratio ϕ = 0.13–2.     

Inhibition of various hydrogen combustion regimes in air by Propylene and Isopropanol

This paper studies the effects of small additives of propylene and isopropanol on the hydrogen-air flame speed in the predetonation regime, deflagration-to-detonation transition, and burning rate. It is shown that the difference in the effects of these additives on the combustion is determined primarily by their ability to terminate reaction chains. In hydrogen flames, the additives are consumed as a result of their reactions with the active intermediate products of H₂ combustion in which these species are replaced by inactive radicals.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 3–14, January–February, 2005.     

Ignition and Combustion of Dust-Gas Suspensions

The ignition and combustion of dust-gas suspensions are considered. It is shown that the ability of these systems to accumulate heat is determined not only by their kinetic and thermal properties but also by the relation between their reaction surface and the heat-removal surface (f). Experimental information on flame temperatures, ignition delays, and flame propagation over gas suspensions is processed using the parameter f, and the postulate on the stimulating role of the developed reaction surface in activating these processes is validated. It is shown that during overall burning, diffusion combustion of particles occurs only for rather small values of f. The ambiguous effect of the parameter f on the ignition and combustion processes leads to the necessity of optimizing the fuel size distribution and concentration for the effective operation of the power devices. The role of the macroparameters of two-phase flames of refractory metals in the synthesis of combustion nanoproducts is analyzed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 3–14, November–December, 2005.     

Tracer method in numerical simulation of combustion processes

Fuel-rich laminar flat hydrogen-methane-air flames are studied numerically using the tracer method. It is found that, in the near-limit mixture, hydrogen has an advantage in the oxidation by oxygen. As the stoichiometric compositions are approached, this advantage decreases and then disappears. It is shown that H ₂ ^* O and CO ₂ ^* labeled additives participate in the reactions and the labels from these molecules move to other products. Small additives of CH ₄ ^* in the mixture completely react to form HH*O, H ₂ ^* O, CO, CO₂, HH*, and H ₂ ^* . Quantitative data on the distribution of the tracer atoms in products are given. The interaction of the hydrogen and methane oxidation schemes is studied. It is shown that in the presence of restriction on the interaction of these schemes, the laminar flame velocity increases by a factor of 5–7. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 3–12, November–December, 2007.     

Competing chemical transformations in the combustion wave in the Fe2O3-Cr2O3-Al mixture

Laws of combustion of a thermit-type mixture Fe₂O₃-2Al-γCr₂O₃ are considered. The limits of liquid-phase combustion and separation of the oxide and metal phases in the final products are determined. Chromium oxide is demonstrated to weakly compete with iron oxide in the oxidation-reduction reaction with aluminum and to participate mainly in oxide-phase formation. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 89–91, May–June, 2006.     

Combustion of thermite systems with orthogonal orientation of the overload and combustion-velocity vectors

The mechanism of combustion of the Fe₂O₃+Cr₂O₃+Al+C system in a field of centrifugal forces with orthogonal orientation of the overload and combustion-velocity vectors is studied. It is shown that a centrifugal force has a pronounced effect on the combustion mechanism and velocity. It is found that the flow of gaseous combustion products strongly influences the dependence of the combustion velocity on the magnitude of overload. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 57–60, January–February, 1998     

Catalysis and inhibition of the combustion of ammonium perchlorate based solid propellants

Results of studies of the combustion of a composite solid propellant based on ammonium perchlorate are presented. The effect of additives of metal oxides is studied for the high and low-temperature decompositions, linear pyrolysis, and combustion of ammonium perchlorate, the decomposition of HClO₄, isobutylene oxidation by oxygen and perchloric acid, and the combustion of propellants with various organic combustibles. It is shown that the efficiency of metal oxides in the reactions of oxidation of isobutylene and propellant combustion is related to the energy of the Me—O bond in the surface oxide layer or the enthalpy of formation of this bond. The extremal nature of the catalytic effect of metal oxides on the burning rate of the propellant is due to the small time of residence of the oxide particles in the zone of intense oxidation-reduction reactions. For this reason, the same additives of metal oxides has different effects on the combustion of the propellant with different organic, combustibles, and the most efficient catalyst can be chosen by a simplified algorithm. The potentials for affecting the composite solid propellant via gas-phase oxidation-reduction reactions is indicated by the effect of additives of organic sources of active species—amines and halides. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 76–90, November–December 1999.     

Flame propagation in mixtures of monogermane and oxygen. II. Peculiarities of flame propagation and the structure of combustion waves

Different flame propagation regimes, including a two-wave regime, are studied in a closed pipe with single ignition of GeH₄−O₂ mixtures. It is shown that, depending on the initial conditions and, in particular, on the composition of the initial mixtures, spatially separated chemical reaction waves for oxidation and decomposition of monogermane are observed in certain parts of the reaction vessel which lead to the formation of a two-layer deposit of GeO/Ge. The temporal sequence of the separated combustion wave and wave from which layers of solid products are deposited, as well as the location of the deposition zones in the reaction vessel, are determined by two interacting chain processes—the oxidation and decomposition of monogermane. The thermal relaxation kinetics of the reactive mixture after passage of the combustion waves is determined by the rate of conductive heat transfer from heated solid particles (reaction products) to the gaseous phase. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 77–84, January–February 1999.     

Ammoximation of methyl ethyl ketone with H2O2 and ammonia over TS‐1

The ammoximation of methyl ethyl ketone and hydrogen peroxide to form methyl ethyl ketoxime was studied over zeolites (TS‐1) in the temperature range 308–373 K. The reaction was carried out in a batch autoclave at autogenous pressure. The conversion of methyl ethyl ketone and the selectivity to methyl ethyl ketoxime can reach 99% and approximately 100%, respectively, and the by‐products were the small amounts of corresponding methyl ethyl ketazine and trace amounts of unidentified compounds. Important factors were the reaction temperature, solvents and slow addition of hydrogen peroxide. The molar ratio of NH₃ to ketone had no significant effect on the conversion of methyl ethyl ketone, but increase in the ratio of NH₃ to ketone had a beneficial effect on selectivity. Copyright © 2006 Society of Chemical Industry     

Effect of the addition of ultrafine aluminum powders on the rheological properties and burning rate of energetic condensed systems

The effect of small additives (1.25–5.00%) of ultrafine aluminum powders (UFAP) on the rheology and combustion of model four-component energetic condensed systems is studied. It is found that the addition of UFAP decreases the temperature of HMX decomposition. Small additives of UFAP increase the burning rate of model energetic condensed systems and decrease the exponent ν in the burning rate law without deteriorating the rheological characteristics of the model propellants. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 54–59, January–February, 2007.     

Effect of heat release conditions on the phase composition of the combustion products of a Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Al/C thermite mixture

An X-ray method was used to study the phase composition of the combustion products of a Fe₂O₃/TiO₂/Al/C thermite composite mixture, in particular, during combustion of samples under cooling by water. The data of the experiments are compared with the results of thermodynamic calculations. A probable explanation of the reasons of the angular displacement of the line of iron in the X-ray spectrum of the combustion products and a mechanism for the crystallization of an eutectic TiC + α-Fe mixture from the melt of the Ti/Fe/C ternary system. The composition of the combustion products was found to be different from the equilibrium one, which is manifested in the presence of defects in the carbon sublattice of titanium carbide. A probable explanation of the deficiency of carbon is proposed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 4, pp. 39–43, July–August, 2008.     

Laser Ignition of Various Pyrotechnic Mixtures – an Experimental Study

Ignition of several pyrotechnic mixtures by diode‐laser was studied experimentally using a novel combustion chamber. The ignition delay times dependence on laser intensity could be fit by the expression t_ign=aI⁻ⁿ for all compositions, with I being the laser intensity at target and n=1.4–2.1. This is roughly in accordance with thermal ignition theories assuming a semi‐inert solid. Differences in ignition delay times did not depend on fuel alone or oxidizer alone. The temperature of oxidizer decomposition does not correlate with ignition delay time. Furthermore, the steady state combustion temperature, deduced from emission spectra of the composition products are not correlated with ignition delay time. It is proposed that chemical reactions, taking place in the gas‐phase or in the solid‐phase, play a significant role, but are not solely responsible for ignition delay time. The seemingly uncorrelated ignition delay results between pyrotechnics containing either the same fuel or oxidizer hamper the construction of a “unified theory” for laser ignition of pyrotechnic mixtures.     

Macroscopic and microscopic aspects of product formation in the Fe2O3-TiO2-Al disperse system burning in the SHS regime

The macromorphology and micromorphology of the combustion products of a Fe₂O₃-TiO₂-Al powder mixture burning in the regime of self-propagating high-temperature synthesis were studied. Significant differences were found in the structure of the products with variation in the ratio of the mixture components. A mechanism for shape and phase formation was proposed that allows the observed differences to be explained from unified positions. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 79–88, May–June, 2006.