Home – Home – Jornals – Combustion, Explosion and Shock Waves 2026 number 4

Using the detailed kinetic mechanism of GRI-Mech 3.0, a computational verification of the applicability limits of Zel’dovich's assumption on quasi-equilibrium concentrations of atomic N in NO formation reactions via the thermal mechanism in a methane-air diffusion flame at high process pressures and temperatures was performed. In contrast to Zel’dovich's assumption, with an increase in the flame diffusion rate (χ _st ), the CH + N₂ reaction becomes the main source of nonequilibrium N compared to the O + N₂ reaction, but only a portion (62 ÷ 87 %) of the released N directly participates in oxidation reactions. As a result, the rates of the N + O₂ and N + OH reactions in the Zeldovich mechanism increase by 30 and 26 times, respectively, while under the assumption of a quasi-equilibrium N concentration, their overall rate increases by only 30 %. It is shown that this assumption in the Zeldovich thermal mechanism is applicable in the range of χ _st = 1 ÷ 8 s^-1, with the calculated NO _x emission index values deviating within ±37 % at the extremes of this range.

The phenomenon of superadiabatic temperatures (SAFT) in flames of rich ammonia and hydrogen mixtures with air was studied using numerical methods. It was shown that the superadiabatic temperatures in these flames are due to the fact that unreacted ammonia remains in the flame front by the time the oxygen is completely consumed and the water concentration reaches its maximum value. Its dissociation in the post-flame zone leads to a decrease in temperature, an increase in the hydrogen and nitrogen concentrations, and, correspondingly, a decrease in the water concentration due to the increase in the number of moles. The somewhat preferential oxidation of ammonia compared to hydrogen in the flame front temperature range from the initial to the maximum value also contributes to the SAFT level.

The main components of natural gas are methane and ethane. Despite their widespread use, gas mixtures are explosive. This paper studies the explosion characteristics of a premixed methane-ethane-air mixture (fuel equivalence ratio ϕ = 0.7 ÷ 1.3) in a 1 m³ spherical chamber, as well as the explosion suppression effect upon adding an inert N₂/CO₂ mixture. The inhibition mechanism is analyzed from the standpoint of chemical kinetics. The results show that the maximum explosion intensity, characterized by peak pressure and maximum rate of pressure rise, is observed with a slightly enriched mixture (ϕ = 1.1). The deformed flame front propagation velocity is 2.60 m/s, the maximum explosion pressure is 830.58 kPa, and the maximum rate of pressure rise is 10.31 MPa/s. The ten key elementary reactions that most significantly affect the concentration of reactive radicals (H•, O•, OH•) and the explosion temperature coincide; their sensitivity coefficients change in the same direction. At the same volume fraction of inert gas, increasing the CO₂ content in the N₂/CO₂ mixture enhances explosion suppression. This is explained not only by the higher heat capacity of CO₂ but also by its direct participation in elementary reactions, leading to the termination of branching chains and the formation of stable products. Complete explosion suppression is achieved with the introduction of 25% (volume) of the inert mixture.

From the standpoint of explosion safety of flammable mixtures, critical initiation energy data are most important, allowing for an analysis of the relative hazard of various mixtures. Critical energies E* are defined as the minimum initiator energies that ensure ignition and subsequent propagation of combustion and detonation waves in the mixture under study: the lower the E*, the more hazardous the mixture. Traditionally, initiation energy increases significantly when mixtures are diluted with nitrogen (replacing oxygen with air), when moving away from stoichiometry toward concentration limits, and when the initial pressure decreases. The effect of temperature is less clear and has not been studied in sufficient detail. In this paper, the role of the initial mixture temperature is analyzed using the example of a difficult-to-initiate ammonia-oxygen-nitrogen mixture, not only stoichiometric but also lean and rich compositions. The most interesting and important gas-dynamic and kinetic parameters of combustion, explosion, and detonation are presented. A significant difference in the behavior and values of most system parameters was established, indicating a lack of similarity in the chemical processes taking place.

A numerical solution was provided for the problem of three-dimensional unsteady flow of a propane-air mixture with continuously rotating detonation waves in an annular channel between a flat disk and a ring. Critical values of the channel width and the ring inner diameter were determined, limiting the range of their values at which rotating detonation occurs as a result of direct initiation. Computational data were obtained characterizing the dependence of the gas-dynamic flow parameters and integral force characteristics on the channel width and the ring inner diameter.

In a 500 mm diameter vortex radial annular chamber, the modes of continuous spin and pulsating detonation of a water-fuel emulsion (water --- TS-1 kerosene) mixed with cold air with an initial temperature of 293 K were implemented and investigated. The mass fraction of water in the water-fuel emulsion varied in the range of 0.12 ÷ 0.38. At a mass fraction of water no more than 0.16, modes with a single transverse detonation wave were observed in the range of mixture flow rates of 17.7 ÷ 23.54 kg/s at an excess fuel coefficient of 1.0 ÷ 1.53. The rotation velocity of the transverse detonation waves was 1.78 ÷ 2.03 km/s. The upper limit of the continuous spin detonation modes for the mass fraction of water in kerosene was determined -- 0.16 ÷ 0.17. Moreover, in the range of 0.17 to 0.38, pulsating detonation occurs with radial pulsation frequencies of 0.09 to 0.33 kHz. It was shown that with water added to the emulsion in amounts of no more than 16%, the detonation velocity, thrust, and specific impulses are close to those of continuous spin detonation of pure kerosene with air. It was found that with radial air supply (without swirl) and the same specific mixture flow rates, even combustion is absent.

This article presents a review and comparison of methods for calculating detonation product isentropes based on experimental data from a cylinder test using the foreign-made composite explosive Composition B as an example. It is shown that the classical direct numerical modeling method, despite its clear advantages in the accuracy and reproducibility of experimental results, is extremely labor-intensive and significantly depends on the operator's skill in successive approximations and coefficient selection, as well as on the problem settings and approaches used. The analytical method for calculating detonation product isentropes yields significant errors and is not yet suitable for practical application. An alternative is the approach proposed by researchers at the Joint Institute of Chemical Physics of the USSR Academy of Sciences and tested in this study.

The reaction of a material with a Gaussian reactivity distribution undergoing exothermic decomposition is considered. Using a number of approximations, critical conditions for simple heat transfer between the reacting system and the environment can be obtained. The approximate formula reduces to the classical condition for a small reactivity variance. The results of numerical modeling of the burnout dynamics of materials with distributed reactivity are presented.

This paper is devoted to the development of mathematical models and methods for modeling mesoscopic processes of thermal dissipation and heat transfer in a two-phase porous material under shock-wave loading. The focus is on the influence of the temperature dependence of the mechanical properties of the phases on the resulting temperature field of a shock-compressed porous material in the absence and presence of phase transformations. Simplified analogs of the basic mathematical model used to study the temperature state of a two-phase porous material, taking into account the temperature dependence of its mechanical properties, are analyzed in detail.

The theoretical interpretation of experiments that demonstrated the ability of aluminum nanoparticles to promote hydrocarbon combustion requires the development of next-generation aluminum nanoparticle combustion models with high predictive power for not only combustion time but also other nanoparticle combustion characteristics. This paper provides a review of the aluminum nanoparticle combustion models developed to date. Experiments on the combustion of aluminum nanoparticles behind shock waves are discussed. An explanation for the observed dependence of combustion time on oxygen concentration is proposed, based on the concept of molten aluminum oxide as a highly disordered pseudocrystalline structure in which defect equilibrium is established independently of the oxygen partial pressure.

An approach is proposed for determining the reaction characteristics of aluminum particles in an aerosol. This approach takes into account changes in heat and mass transfer mechanisms as the burning particle size decreases, from a continuous-medium regime (the mean free path of gas molecules is significantly greater than the particle diameter) to a free-molecular regime (ultra-small particles). Modeling the combustion of an aluminum particle, taking into account changes in heat and mass transfer regimes and a decrease in oxygen concentration in the air over a range of oxidizer excess ratios from 1.05 to 2.5 and pressures from 0.1 to 4 MPa, allowed us to identify the determining factor in the decrease in the average mass concentration of the oxidizer during particle combustion, leading to an increase in combustion time in the free-molecular regime relative to the combustion time calculated under a continuous-medium assumption.

This article presents an analysis of experimental data on pulsed combustion initiation of Al/CuO nanothermite. An explosive charge, an electric discharge, and a laser diode were used as pulse sources. The process of dispersion of the reaction products in a mixture by a shock wave is examined. Critical parameters (minimum energy and delay) for laser and spark initiation are determined. Specific impulse measurements using nanothermite in a microthruster are presented. Overall, the results demonstrate that high-speed reaction propagation occurs due to the advanced propagation of hot intermediate products in the porous material. The rate of this process largely depends on the pressure gradient and porosity of the initial mixture.

Iron-matrix composites reinforced with dispersed titanium carbide particles, produced by sintering or coating with titanium carbide powder mixtures with steels, find practical application as wear-resistant materials and coatings. Composite powders with a metal-matrix composite structure of titanium carbide and an iron-based binder are used for applying wear-resistant coatings. The possibility of producing such composite powders by synthesis in mechanically activated powder mixtures of Ti-Fe intermetallic compounds with carbon (carbon black) was investigated. It was found that heating powder mixtures of Fe₂Ti and FeTi intermetallic compounds with carbon (carbon black), pre-treated in an Activator-2S planetary mill at an angular acceleration of 40g for 10 min, results in an explosive temperature increase. According to X-ray diffraction analysis and scanning electron microscopy, the thermal explosion is caused by the synthesis of titanium carbide through the reaction of carbon with titanium contained in the Fe₂Ti and FeTi intermetallic compounds. The thermal explosion products, in addition to titanium carbide, contain metallic iron reduced by carbon and a small amount of unreacted Fe₂Ti intermetallic compound. To fully complete the synthesis reaction and obtain only the target products (titanium carbide and iron), an increased duration of mechanical activation of the powder mixtures is required.

The article presents the results of an experimental study of detonation propagation in a charge made of plasticized TATB-based explosive in the form of a hollow cylinder with an inner copper and outer aluminum shell during normal detonation initiation along a line on the outer surface of the charge. In Experiment 1, the characteristics of detonation propagation under the initiator were investigated using an X-ray diffraction method. It was found that in the initiation plane, the velocity of the diverging detonation wave front was 7.4 km/s. In Experiment 2, using a multi-frame proton accelerator, the shape and position of the detonation wave front were determined at various points in time. The original experimental design made it possible to study detonation propagation at angles greater than 180°C from the initiation line. It was shown that in the "shadow" region of the initiation point, the detonation wave velocity along the inner surface of the TATB charge decreases from 7.4 to 6.5 km/s. At an angle of approximately 90°C from the initiation plane, the development of a Kelvin-Helmholtz instability in the form of repeating periodic disturbances was detected on the surface of the copper shell. A disturbance in the form of a "doubling" of the front was detected at the detonation wave front, originating near the surface of the copper shell and propagating along the front surface as it propagated through the charge. Moreover, not only the detonation wave but also the shock wave reflected from the copper shell exhibited a "double" front. The positions of the shells during expansion and the fronts of the reflected shock waves in the explosion products were recorded. Using a heterodyne interferometer (PDV) method, the velocities of the inner and outer shells were continuously recorded. The obtained data can be used to calibrate numerical models incorporating detonation kinetics and the equations of state of the TATB explosion products. Experimental dependences of the detonation wave front velocity on the front curvature were obtained and compared with data from other authors.

Penetrating munitions charges must meet stringent requirements, including high energy density, excellent mechanical properties, and low sensitivity to environmental influences. To increase the energy density of the aluminized explosive, a hydroxyl-terminated fluorinated oligomer (HTFB) was added to the cast PBX composition as a binder. Using a mix/pour/curing method with an 88% solids content, a curing system for aluminized cast PBX was developed and studied. Factors influencing the rheological characteristics, molding processes during curing, and the mechanical properties of the composition were studied. The mechanical and detonation characteristics of the resulting compositions were determined, as well as their sensitivity to external influences during limited storage time under conditions requiring rapid access to ammunition. The results showed that the PBX-361-C composition offers the best combination of pouring processability and cured casting quality. Its density, heat of detonation, and velocity of detonation are 1.962 g/cm³, 7 806 J/g, and 7 603 m/s, respectively. The tensile and compressive strengths of PBX-361-C are 9.33 and 37.53 MPa, respectively. During rapid and slow heating tests, as well as during bullet firing, the reaction of the composition was limited to combustion or weaker forms. The estimated shelf life of PBX-361-C at room temperature is 7,442 years. All the data obtained indicate the high potential of this composite system for use in penetrating munitions.

The results of numerical simulations using the smooth particle simulation (SPH) method for an oblique symmetrical impact of aluminum plates are presented. These simulations are used to propose a model for wave formation at the plate contact interface. Wave formation is caused by self-oscillations that develop due to the instability of the symmetrical flow and are sustained by the energy of the colliding plates. In the contact region, the material is softened due to heating, so the plate collision can be modeled as an oblique impact of liquid jets. During the oblique impact of the jets, a forward and a reverse jet are formed. Due to disturbances arriving at the contact point, the spreading points of the interacting jets shift, creating a force dipole whose oscillations generate oscillations in the forward and reverse jets. After the forward jet leaves the contact region, its strength properties are restored, so the oscillations are "frozen" as waves at the contact interface. The calculated wavelength agrees satisfactorily with that observed experimentally. The reverse cumulative jet impacts the plate surface, disintegrates, and transforms into a particle cloud.

Traditional emulsion explosives (HE) are characterized by a contradiction between high energy release and operational safety. To address this issue, the use of a coating layer for aluminum particles was investigated in this study. Microcapsules with a core-shell structure, in which aluminum powder is encapsulated in polymethyl methacrylate (PMMA), were synthesized using suspension polymerization. Paraffin and stearic acid coatings were also formed on the surface of the aluminum particles using solvent evaporation. This allowed a systematic study of the effect of various shell materials on the detonation characteristics of aluminized emulsion explosives. Three groups of emulsion explosive samples were prepared with the addition of the indicated types of coated aluminum powders as an energy additive. The microstructure and coating quality of the aluminum particles were studied using scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The effect of coating structure on the shock wave parameters and thermal stability of aluminized emulsion explosives was studied using a pneumatic testing system and a DSC-TG synchronous thermal analyzer. Experimental results show that the PMMA coating forms a continuous, dense shell, while paraffin and stearic acid coatings exhibit localized defects. All three types of coated aluminum powders enhance the shock wave parameters of the emulsion explosive, with the best effect achieved for PMMA and aluminum microcapsules: the peak shock wave pressure increases by 25.1% compared to the control sample. The PMMA shell increases the activation energy of the aluminized emulsion explosive, thereby improving its thermal stability. Paraffin and stearic acid coatings reduce the activation energy due to the presence of defects at the interface. Microencapsulation technology in PMMA, by forming a dense core-shell structure, simultaneously increases the energy density and thermal stability of emulsion explosives, making it promising for the production of high-energy, insensitive emulsion formulations.

Hydrogen-storage alloys, a typical example of which is MgH₂, are attracting considerable interest as potential components for enhancing the performance of energetic materials. To study the effect of vacuum depression on detonation parameters, RDX-based composite explosive samples with varying MgH₂ powder contents were manufactured. Using a spherical explosion chamber and color pyrometry, shock wave parameters and temperature fields were analyzed depending on the vacuum depression. Experiments have shown that RDX/MgH₂ composite compositions outperform pure RDX in detonation characteristics and thermal damage potential. With increasing vacuum, peak pressure and positive impulse decrease, the duration of the positive phase varies non-monotonically, and thermal damage performance also improves within a certain range. A comparative analysis of the effects of MgH₂ and Mg additives on the explosion characteristics of RDX compositions at atmospheric pressure and in high vacuum conditions revealed that MgH₂ provides a significantly more pronounced positive effect on the shock wave parameters, as well as on the volume and lifetime of the fireball. These results suggest that MgH₂ powder can be considered a promising energy additive for the creation of new, highly effective high-explosive compositions.