Kinetics of Chemical Reactions During Detonation of Mixtures of Organic Substances with Nitric Acid

The kinetics and mechanism of chemical reactions in detonation waves propagating in mixtures of nitric acid with nitroglycol, ethylene glycol dinitrate, and acetic anhydride were studied within the framework of the Dremin—Trofimov theory of the detonation failure diameter. The state parameters in shock and detonation waves were calculated using the SGKR software package. It was shown that the decomposition of mixtures of nitric acid with organic substances in a detonation wave is a complex reaction which includes several stages. Various kinetic models are considered; effective values of the kinetic parameters are calculated for each model and for the entire process.     

Measurement and chemical kinetic prediction of detonation sensitivity and cellular structure characteristics in dimethyl ether-oxygen mixtures

In this work, experiments have been performed to measure the detonation velocities and characteristic cell sizes in the dimethyl ether (DME) fuel-oxygen mixtures. Equilibrium calculation and detailed chemical kinetics modeling of the ZND structure of detonations are also carried out to investigate the detonation characteristics of DME. Detonation cell sizes estimated using a correlation model by Ng et al. [Ng HD, Ju Y, Lee JHS. Assessment of detonation hazards in high-pressure hydrogen storage from chemical sensitivity analysis. Int J Hydrogen Energy 2007;32:93-99] are in good agreement with experimental data. It is found that the cell size values for DME-oxygen mixtures are comparable to those of propane or ethane fuels. At low initial pressure, double cell like detonation structures have been observed in all equivalence ratios considered in this study. Chemical kinetic results reveal that DME oxidation under detonation environment exhibits similarly a two-stage heat release process inside the reaction zone. This effect may play a significant role in the existence and scaling of the multi-cell detonation pattern in stoichiometric and fuel-rich DME mixtures. On the lean side, multiple cells appear to be caused primarily by the strong intrinsic instability of the unsteady detonation front. The present experimental results and chemical kinetic sensitivity analyses provide some basic information to assess detonation hazards in DME-based mixtures.     

Two-dimensional cellular structure of a kinetically unstable detonation front

Based on previously published results on the detonation of gaseous and liquid explosives, an explanation is given to the formation of the two-dimensional cellular structure of the detonation front of some gas mixtures undergoing a two-step exothermic transformation at the wave front and suggestions are proposed for the mechanism of development of the two-dimensional cellular structure in the case of detonation transformation of gas mixtures with one-step chemical kinetics. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 4, pp. 80–86, July–August, 2008.     

Detonation characteristics of diluted liquid explosives: Mixtures of nitromethane with methanol

Detonation in mixtures of nitromethane with methanol as an inert (nonexplosive) diluent is studied. Ignition experiments with mixtures in steel tubes of various diameters provided information on the effect of the degree of dilution on detonability. Mass velocity profiles with a chemical spike characteristic of detonation waves were recorded at the unsteady detonation front in all mixtures studied. This made it possible to distinguish the Chapman-Jouguet state and obtain a fairly complete set of detonation parameters. The dependence of the pressure in the detonation products on the methanol concentration is determined, which is required, in particular, to find the true (absolute) limit of detonation propagation for the concentration of diluted liquid explosives using the method proposed and validated by A. N. Dremin. Some results were found to be inconsistent with one-dimensional detonation theory.     

Numerical simulation of the deflagration to detonation transition

The present work is focused on the numerical simulation of the deflagration to detonation transition. The Euler equations expressed for a time-dependent, compressible, and one-dimensional flow with finite-rate kinetics are solved with adaptive mesh refinement. Because of the problem stiffness, a time-step splitting method is used to couple the conservation equations and the chemical kinetics equations. The calculated length of the deflagration to detonation transition in H₂-O₂ and CH₄-O₂ mixtures in a confined domain and the time evolution of detonation are in good agreement with the theoretical values of constant volume explosions and Chapman-Jouguet conditions. The length of the transitional region is compared with experimental findings for a range of initial fuel concentrations, which shows that the model predicts the tendencies qualitatively well but yields significant quantitative deviations.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 2, pp. 108–115, March–April, 2005.     

Initiation of detonation of fuel-air mixtures in a flow-type annular combustor

Initiation of detonation in a fuel-air mixture flow formed in an annular cylindrical combustor 306 mm in diameter is studied. The source of detonation initiation is the detonation wave entering the annular channel from a plane-radial vortex chamber, a jet of products, or a low-power heat pulse. It is demonstrated that continuous spin detonation (CSD) can be ensured by all these methods. Its formation is accompanied by a transitional process with a duration up to 10 ms, which is associated with violation of injection of the species (initiation by the detonation wave) or with the time of evolution of tangential instability in CSD (jet or spark initiation). Transfer of detonation to a flow of fuel-air mixtures with low chemical activity (propane-air, methane-air, kerosene-air, and gasoline-air mixtures) by the initiating detonation wave formed within fractions of a millisecond by a low-energy pulse or as a result of self-ignition of the hydrogen-air mixture in the plane-radial vortex chamber is realized. It is found that organization of CSD in these mixtures requires combustors with greater (than 306 mm) diameters. A possibility of CSD in kerosene-air and gasoline-air mixtures with low chemical activity by means of air enrichment by oxygen ahead of the combustor entrance is demonstrated.     

Through a glass,darkly: Kinetics and reactors for complex mixtures syncrude innovation award lecture

The concepts of chemical reaction engineering are powerful, because the most basic design equations are applicable to a wide range of physical phenomena. For example, the applicability of the ideal continuous-flow stirred tank reactor goes far beyond chemical reactors to include biological, medical and environmental processes. The difficulty in analyzing these processes is not in formulating an appropriate reactor equation, but in modeling the chemical kinetics. The challenge is to define kinetic rate equations that allow for the mixtures of reactants and mixtures of catalysts, especially given incomplete information. Examples drawn from biology and medicine illustrate reaction kinetics that are complex due to the nature of the catalyst. In contrast, processes for upgrading of bitumen to more valuable products exhibit ill-defined reaction chemistry and mixtures of thousands of reactants and products. The need to define kinetics for such mixtures has given rise to several distinct approaches, including empirical rate equations, simplification to model reactions, lumped kinetics and Monte Carlo simulation. A summary of these methods shows that the key element for successful kinetic modeling is creative definition of a model, followed by vigorous testing of the model to determine its ability to predict performance.     

Effect of nitrogen on multifront detonation parameters

A faster increase in the cell size and other very important multifront detonation parameters compared with that predicted by the kinetic calculations has been shown for nitrogen-diluted fuel-oxygen mixtures of hydrogen and typical hydrocarbons. Dilution of mixtures with other inert gases does not lead to a similar effect. This may be associated with the increase in the chemical reactivity of nitrogen under the action of the electric field of a detonation wave. A more correct method of calculating the ignition delays of various nitrogen-containing mixtures for detonation conditions is proposed. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 79–83, January–February, 1998     

Comparison between the shock wave and chemical initiation in detonation of acetylene—oxygen mixtures

Detonation of different compositions of acetylene-oxygen mixtures by both chlorine gas injection and a shock wave as initiators is studied in this research. The chlorine gas is injected into the detonation tube through a reticular plate nozzle at the moment when a thin aluminum foil separating the injection system from the detonation tube is torn by a pressurized nitrogen gas. The results of experiments show that chemical initiation may be as effective as direct initiation of detonation and, therefore, replace more complicated methods of initiation. The best results are obtained in acetylene— oxygen mixtures with the molar ratio of 1: 1.     

Detonation characteristics of diluted liquid explosives: Mixtures of tetranitromethane with methanol

Studies of the nature and mechanism of the concentration limit of detonation propagation in dilution of liquid explosives by non-explosive liquids are continued. The impact of dilution of tetranitromethane by methanol on the process of detonation was studied in a wide range of diluent concentrations. Experiments on the ignition of mixtures in steel tubes of various diameter were perfomed to obtain Data on the critical (limiting) diameters. The results obtained were compared with those from previous studies of mixtures of nitromethane with methanol and nitrobenzene. Differences caused by the chemical interaction of tetranitromethane as an active oxidizer with methanol as a fuel component are considered.     

Use of chemical kinetics to predict critical parameters of gaseous detonations

Computational modeling of chemical kinetics of fuel oxidation under conditions similar to those encountered in detonation waves is described. Sample applications to predicting critical detonation parameters are described, including lean and rich limits to detonation in linear tubes, direct initiation of unconfined spherical detonations by means of high explosive charges or by transition from a linear tube, and kinetic inhibition of detonation.     

Effect of chemically active additives on the detonation wave velocity and the detonation limits in lean mixtures

On the basis of the formalism of the one-dimensional theory of detonation with heat losses and the theory of branched-chain processes by the example of the oxidation of hydrogen-air mixtures in the presence of a hydrocarbon additive, it is shown that taking into account the reactions of termination of reaction chains on molecules of the additive, trimolecular termination, and also chain oxidation of the hydrocarbon additive allows one to qualitatively describe both the passage of the detonation velocity through a maximum with an increase in the additive content of a lean mixture and the existence of two concentration limits of detonation.     

Detonation Limits of Air Mixtures with Two-Component Gaseous Fuels

The problem of detonation limits for ternary mixtures of air with a two-component gaseous fuel is considered for a detonation region represented using the Le Chatelier rule. Examples are given of incorrect treatment of conditions for detonation suppression in hydrogen–air mixtures by the addition of hydrocarbons ignoring the overall composition of the mixture. It is suggested that the range of explosion hazard of lean hydrogen–air mixtures is extended by the addition of small amounts of hydrocarbon gases. Key words: detonation, detonation limits, multicomponent fuel mixtures, suppression and promotion of detonation.     

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.     

Explosive Mixtures Detonating at Low Velocity

Same explosive mixtures detonating at a low velocity and not containing high explosives were experimentally investigated. As a system providing detonation capability, a mixture of ammonium nitrate and powdered aluminium was employed. Glass or urea‐formaldehyde resin beads or lead oxides were used to reduce detonation parameters. Detonation velocity and critical diameter were measured for mixtures differentiated in composition and density. As a result of the investigation, a number of explosives were worked out which are characterized by the capability of stable detonation at a very low velocity (below 1000 m/s) and simultaneously, some of them have a relatively high density (even over 2 g/cm³). An attempt of physical and chemical interpretation of the results obtained is also included.     

A generalized model of the kinetics of chemical reactions in hydrogen-oxygen gas mixtures

A generalized model of the kinetics of chemical reactions, which comprises two equations and satisfactorily describes the whole course of reactions in hydrogen–oxygen mixtures in a wide range of pressure and temperature, is constructed on the basis of an examination of a model gas.Lavrent'ev Institute of Hydrodynamics, Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 1, pp. 66–72, January–February, 1994.     

Dependences of the detonation velocity and propellant performance of metallized explosives on the charge density and additive content

The dependences of the detonation velocity and the propellant performance measured using the M-40 technique on the charge density for aluminized explosives with different mass fraction of Al were studied. The fractions of the energy of Al combustion utilized during the chemical reactions and during the acceleration of the flyer plate were estimated. Regression dependences of the detonation velocity and the propellant performance on the charge density were obtained. The effect of the addition of particulate Al, Ti, Zr, and W in an amount of 5–30% on the detonation velocity of high-density explosive charges based on plasticized RDX was investigated. It is found that the reduction in the detonation velocity with the addition of various metallic additives is determined by the longitudinal sound velocity of the additive, and not by its density. Simple formulas for calculating the detonation parameters of high-density metallized explosives were obtained.     

Studies of Detonation Characteristics of Aluminum Enriched RDX Compositions

Research on the effect of aluminum contents and of its particle size on detonation characteristics of RDX‐based compositions containing 15–60% aluminum was carried out. Measurements of detonation velocity for different charge diameters and confinements were performed. To measure the shock curvature of the detonation wave, X‐ray photography was applied. Unconfined charges and charges confined with a water envelope were tested. The radius of the detonation front curvature was determined. The cylinder test results were the basis for determination of the acceleration ability and energetic characteristics of the detonation products of the mixtures. The Gurney energy describing the acceleration ability was found. The detonation energy of the mixtures tested was also estimated from the cylinder test data.     

Detonation velocity of highly dispersed ammonium perchlorate and its mixtures with explosive substances

This paper describes the measurement of the detonation velocities close to ideal velocity relative to large charges of highly dispersed ammonium perchlorate (AP) and its mixtures with different explosive substances in thick-walled steel pipes. The relationship of the detonation velocity of AP with its density and the relationship between the detonation velocity of mixtures with the component ratios and oxygen coefficient of the mixtures are determined. The calculation of the detonation velocity of AP/explosive/Al three-component compositions is proposed for the first time.     

Deflagration-to-detonation transition in isopropyl nitrate mist/air mixtures

The characteristics and stages of the deflagration-to-detonation transition (DDT) in isopropyl nitrate (IPN) mist/air mixtures are studied and analyzed. A self-sustained detonation wave forms, as is observed from the existence of a transverse wave and a spinning wave structure. The run-up distance of the DDT process and the pitch size of the self-sustained spinning detonation wave in IPN/air mixtures are analyzed. Moreover, a retonation wave forms during the DDT process. Two propagation modes, the high-speed deflagration mode and the self-sustained detonation mode, of the shock-reaction complex (SRC) in IPN mist/air mixtures are found and analyzed. The influence of the mist concentration on the SRC propagation mechanism is studied. The minimum and the optimum IPN mist concentrations for DDT occurrence in IPN mist/air mixtures are determined. The propagation velocity and overpressure of the self-sustained detonation wave in IPN mist/air mixtures are measured and calculated.