Home – Home – Jornals – Combustion, Explosion and Shock Waves 2025 number 5

A generalized two-stage model of chemical kinetics of detonation combustion of a binary stoichiometric mixture of methane with hydrogen and air is proposed. It allows calculating the heat release of the chemical reaction, the molar mass, the internal energy and the adiabatic index of the mixture without calculating its detailed chemical composition, which significantly simplifies kinetic calculations and reduces their volume compared to detailed kinetics. The model is physically substantiated and does not contain adjustable parameters. For the mixture under consideration, a numerical two-dimensional calculation of the multifront structure of the detonation wave was made with a variation in the ratio between the combustibles. Chemical transformations were described using the proposed kinetic model. The calculated size of the detonation cell, as well as the qualitative structure of the detonation wave (the presence of regions of unburned gas in the reaction zone and the irregularity of the cellular structure caused by the formation of both primary and secondary transverse waves) are in good agreement with the experiment.

In order to study the combustion stabilization mechanisms, the gas parameters near the flame leading edge behind the rib and behind the step in the boundary layer with ethanol evaporation and combustion were compared. It was shown that at an air flow velocity of ≈11 m/s, an attached flame is formed behind the step, and the ethanol evaporation intensity is lower than behind the rib with a detached flame. At the flame leading edge behind the barriers, a zone is localized where the maximum heat release is located at the mixture ignition temperature, and the static and dynamic pressures are equal. It was shown that under conditions of gas motion with combustion and separation behind the rib, the maximum contribution of turbulent momentum transfer reaches ≈30 ÷ 40% of the averaged convective, and the share of molecular transfer is 2 ÷ 3%.

The non-stationary self-ignition of a hydrogen-air mixture that has not been prepared in advance in a high-speed flow is considered in order to clarify the effect of the fuel excess factor on ignition and combustion stabilization in the channel. A series of experiments in a wide range of fuel excess factors of 0.35 ÷ 1.2 showed that the initial ignition occurs in the boundary layer separation zone under the influence of a re-reflected bow shock wave in front of the fuel jet. This zone is a stable ignition source, from which the flame, under certain conditions, propagates upstream to the channel entrance. There are two combustion stabilization modes at an injection angle of 45°. At low fuel excess factors, a flow with a monotonic pressure increase is realized until a plateau with a moderate pressure increase is reached. At a fuel excess factor of more than 0.8, a two-stage combustion mode is realized. The first stage consists of the heat supply process, which coincides with the combustion mode at low excess fuel coefficients and is characterized by an increase in pulsations due to increased thermoacoustic interaction. As a result of the increase in pressure in the initial ignition region, the flame front rapidly propagates up and down the flow and the pressure increases to maximum values at high combustion completeness. A comparative analysis of the pressure and heat flux distribution along the channel length is performed.

Macrokinetic regularities of high-temperature transformations of a number of s-triazine derivatives containing azide, propynyl oxide and propynyl amine functional groups have been investigated. It has been shown that these compounds are capable of self-propagating high-temperature transformation (combustion) in the absence of an external oxidizer. Linear combustion rates in a nitrogen environment are proportional to the enthalpies of formation of the corresponding s-triazine derivatives. Diazide derivatives burn with the highest rates, lower combustion rates correspond to compounds containing three acetylene groups. Thermal decomposition of azidoacetylene derivatives of s-triazine has been studied using thermogravimetry and differential scanning calorimetry. Thermal analysis has shown that the most stable compound in the studied series of samples is the compound containing three propynyl amine groups, the least stable are the diazide derivatives of s-triazine.

The results of an experimental study of the effect of a weak transverse constant electric field on the temperature distribution in a laminar flame of a Bunsen burner are presented. Using the method of planar laser-induced fluorescence, temperature fields in flames of pre-mixed lean methane and propane-air mixtures were obtained in the presence and absence of an external electric field. The results of visualization and evaluation of the temperature field indicate that the presence of an electric field leads to a change in the shape of the flame front and its deviation to the cathode, but does not significantly change the temperature distribution in the flame under study.

The results of numerical modeling and experimental data related to combustion in a porous medium of a cylindrical burner with axial fuel feed are presented. The modeling of filtration combustion is performed within the framework of a two-temperature thermal diffusion model taking into account radiative heat exchange on the surfaces. The results of numerical modeling allow us to estimate the temperature distribution in the gas and in the porous layer, as well as the radiation fluxes inside and outside the cylindrical porous layer. The calculated results are in satisfactory agreement with the experimental data obtained during combustion of a propane-air mixture in a burner with a porous layer. The effect of external thermal insulation on the characteristics and efficiency of the burner is discussed.

The effect of the powdered oxidizer (potassium nitrate) particle size on the combustion law of a model energetic condensed system in the pressure range of 0.5 ÷ 40 MPa was experimentally determined using the microwave method of contactless diagnostics. The model composition of the system based on an epoxy combustible binder, potassium nitrate and a combustion modifier --- iron oxide Fe₂O₃ was studied. Random errors were taken into account when calculating the experimental values of the linear combustion rate. Analytical dependences of the linear combustion rate of model energetic condensed systems on pressure, approximated by power and linear functions, were obtained. It was found that with a decrease in the particle size of the powdered oxidizer, the value of the transition pressure from the power combustion law to the linear one decreases, while the combustion rate also increases.

The features of high-temperature synthesis wave propagation through an air gap are considered experimentally and by calculation and theory. Cylindrical samples made from a charge of different compositions were used. Critical values of the air gap width were found, at which the combustion wave transition from one sample to another is still possible. Depending on the parameters of the reacting mixture, the effective radiation coefficient from the end surface of the burning sample was calculated on the basis of the constructed mathematical model, consistent with the experimental data.

Nitrogen oxides N_xO_y, as environmentally hazardous substances, have long attracted the attention of researchers. In addition, they also represent systems of fuel and oxidizing components (monofuels). Such monofuels are capable of exploding, which must be taken into account when assessing their explosion safety. The article presents the combustion and detonation parameters of the most well-known gaseous nitrogen oxides when interacting with oxygen, which are important for hazard assessments.

The combustion of aluminum agglomerate particles with a diameter of 215 ÷ 840 μm in free fall in air at atmospheric pressure is investigated. The main events of the particle combustion process after their exit from the sample into the air --- change from symmetrical combustion to asymmetrical, fragmentation, end of combustion --- are characterized by the corresponding times. Approximating dependences on the particle diameter are obtained for the characteristic times of the symmetrical combustion stage, the beginning of fragmentation, the end of fragmentation, and the end of combustion. The characteristics of particle fragmentation are determined. Data are given on the relative number of parent agglomerate particles emitting a certain number of fragments, and on the dependence of the number of fragments on the diameter of the burning particle. For larger particles, fragmentation begins later, but proceeds more intensively. In general, the observed spontaneous fragmentation of aluminum agglomerates is insignificant, therefore, in order to reduce their combustion time, a targeted intensification of the fragmentation process is necessary.

The volume-temperature dependence of the specific electrical resistance of manganin in the pressure range of 5 ÷ 70 GPa and temperatures of 300 ÷ 1,000 K of step shock compression is investigated. The electrical resistance of manganin samples is measured under dynamic loading by plane one-dimensional shock waves. Thermal and caloric equations of state of manganin are developed, using which the volume-temperature dependence of the specific electrical resistance of shock-compressed manganin is reconstructed. Under the assumption of reversibility of the specific electrical resistance of the metal, a semi-empirical model of the change in the specific electrical resistance of manganin under compression and unloading, including the hysteresis effect of the manganin sensor, is formulated.

For a set of substances representing all the main classes of explosive compounds, the relationship between the critical autoignition temperature calculated using the maximum heat of explosion and kinetic parameters (activation energy and pre-exponential factor) of the decomposition reaction in the liquid phase, and the sensitivity index h₅₀ was analyzed. The found correlation equation can be used to predict the sensitivity of new compounds. The relationship between the sensitivity of compounds and their structure was analyzed.

An approach to determining the degree of decomposition of plasticized octogen at different ambient temperatures is presented. A scheme of works aimed at determining the temperature-time conditions of accelerated aging of plasticized octogen and establishing guaranteed periods of storage and operation of plasticized octogen is proposed. For calculations, a model of kinetics of slow decomposition of the studied explosive substance, constructed on the basis of heat release data obtained by differential scanning calorimetry, is used. The application of the presented model allows to estimate the shelf life and operation of explosive substances based on the degree of decomposition indicator.

A new empirical method for predicting detonation pressure of various types of organic and inorganic explosives is presented. The method identifies detonation products by the product that releases the maximum amount of heat per oxygen atom. The proposed model provides accurate and reliable estimates of detonation products compared to existing models. Using these identified products, detonation parameters such as the number of moles of gaseous products, their average molecular weight, and the maximum heat of detonation are calculated. A power-law relationship is established between the detonation parameter and experimental values of detonation pressure for different explosives. Unlike other models, the detonation pressure calculated by the new model agrees well with the experimental values for organic and inorganic explosives. These results indicate that detonation pressure predictions based on the new model are simple, accurate, and more reliable than those based on existing models, thereby contributing to the development of environmentally friendly, high-performance explosives.

Experiments and numerical modeling of the jet formation process and target penetration characteristics by micro-cumulative charges with polymer liners were conducted. The influence of the liner material, the distance from the charge to the target and its structure on the operation of the cumulative charge was analyzed. The results show that, compared to a copper jet, the penetration depth of the polymer jet decreased, and the crater diameter during penetration increased.

As a typical non-cylindrical structure, the prismatic shell with semi-finished fragments is extremely important for the structural design and evaluation of the destruction efficiency of the innovative warhead. The velocity and scattering angles of fragments are important parameters in the creation of the warhead and protective elements. However, the vast majority of existing formulas for the fragment velocity are created specifically for the cylindrical body, and there are very few formulas for calculating the scattering angle as applied to the prismatic body. In this paper, using theoretical analysis, a formula for the fragment velocity from the prismatic body is derived, and equations for both the radial and axial scattering angles of fragments are proposed. The rationality of the formulas was confirmed by experimentally verified numerical results. Ultimately, based on the obtained expressions and orthogonal analysis, the laws of influence of dimensionless geometric parameters on the scattering angle and specific kinetic energy of fragments were established, and the primary and secondary orders of influence of each parameter on the scattering angle and specific kinetic energy were determined, respectively. The results of this work will form the basis for further research into prismatic metal shells and other types of asymmetric shells, as well as a reliable source for the technical design of innovative warheads.