Home – Home – Jornals – Combustion, Explosion and Shock Waves 2022 number 1

Due to the absence of experimental data for constructing the phase diagram of a liquid and gaseous mixture of hydrogen with oxygen, it is constructed by modeling. Model diagrams previously predicted (Deiters et al., 1993) by two methods (I and II) at pressures up to »100 MPa and a temperature up to »100 K have significant differences, which are considered by the authors as an approximate measure of the uncertainty of the knowledge of the real phase diagram of this mixture. In this paper, the phase diagram of a mixture of hydrogen with oxygen is determined using the previously proposed modified van der Waals model for individual and mixed compounds. Calculations were performed in two (A, B) variants differing in the binary interaction parameter. To control these variants, they were used to construct model diagrams of mixtures of hydrogen with nitrogen, argon, and methane for which there are experimental data in the range of pressures and temperatures comparable to those mentioned above for the mixture of hydrogen and oxygen. Variant B is more realistic as it is in better agreement with experiment compared with variant A. The phase diagram calculated by method B for a mixture of hydrogen with oxygen is close to the calculation by method I, which indicates that it is more realistic than method II.

To investigate the mechanism of the flame-vortex interaction induced by an obstacle, a numerical research of premixed methane-air flame dynamics in an obstructed chamber is described. Numerical simulations are performed with the OpenFOAM open-source CFD code. The simulation images show that the flame propagation process can be divided into four typical stages. A series of instabilities are captured in the simulation during flame propagation. More importantly, the numerical results demonstrate that a longer obstacle allows a sufficient accelerating time, which can give rise to a higher explosion overpressure and faster flame tip speed.

The laminar burning velocities of a stoichiometric CH₄-N₂O mixture diluted with N₂ [30 ÷ 60 % (by volume)] at various initial pressures (1 ÷ 10 bar) and various initial temperatures (273 ÷ 423 K) are obtained by numerical modelling of their premixed adiabatic flames. The modelling is performed with the Cosilab package using the GRI-Mech 3.0 mechanism based on 53 chemical species and 325 elementary reactions. The calculated laminar burning velocities are compared with available literature data. The influence of the initial conditions (pressure, temperature, and N₂ concentration) of CH₄-N₂O-N₂ mixtures on the laminar burning velocities, maximum flame temperature, heat release rate, and peak concentrations of the main reaction intermediates is investigated and discussed. Using the correlations of the laminar burning velocities with the initial pressure and the average flame temperature, the overall activation parameters of CH₄-N₂O oxidation are determined.

Regimes of detonation burning of TS-1 aviation kerosene in an air flow in a flow-type radial vortex combustor 500 mm in diameter with exhaustion toward the center are obtained. The parameters varied in experiments are the diameter of the combustor exit cross section (from 250 to 125 mm) and the shape of one of the combustor walls. The air flow rate in detonation burning regimes is 5.23 ÷ 23.85 kg/s, and the kerosene flow rate is 0.49 ÷ 1.2 kg/s. The fuel-to-air equivalence ratio is varied in the interval 0.58-2.24. Kerosene is bubbled with air before its injection into the combustor. Pulsed detonation with radial waves and continuous spin detonation with one rotating detonation wave with a velocity close to the Chapman-Jouguet detonation velocity are observed. The structure of detonation waves and the flow in their vicinity display no principal differences from those observed previously in a plane-radial combustor with a smaller diameter (204 mm). A strong effect of detonation waves in the combustor on the air and kerosene injection systems is detected. Centrifugal forces acting on the mixture flow and detonation products are enhanced as the combustor exit diameter decreases (as the combustor length increases). For identical specific flow rates of kerosene-air mixtures, the pressure near the cylindrical surface of the combustor in idle runs is found to be higher than that in the case of detonation.

Ti₃AlC₂ and Ti₃SiC₂ single-phase MAX phases were obtained by preliminary mechanical activation (MA) of initial mixtures of powder reactants in a high-energy planetary ball mill with subsequent self-propagating high temperature synthesis (SHS). The MA and SHS products were studied by X-ray diffraction and electron microscopy.

The generation of thermoEMF during combustion of titanium and boron powder mixtures under pressure has been studied. It has been shown that when the boron content in the mixture is less than 2.5 mol, thermoEMF is generated in the form of a constant positive signal, at 2.5 < B < 4.0 mol, it is generated in the form of a constant negative signal, and at B > 4.0 mol, in the form of a negative pulse. The generation of a positive signal is due to the electronic conductivity of titanium particles, and the generation of a negative signal is due to the hole conductivity of boron particles. Experimental dependences of the maximum temperature, average burning speed, and the widths of the combustion wave and thermoEMF on the mole fraction of boron in the mixture have been obtained. It has been shown that the greatest width of the combustion wave is about ~10 mm, and its minimum (critical) width is 1 mm.

The combustion of highly exothermic multicomponent mixtures of Co₃O₄/Cr₂O₃/Nb₂O₅/Al with additives of MoO₃, WO₃, and carbon (graphite) under overload up to 200 g has been studied. It has been shown that the introduction of carbon into the initial mixture has a noticeable effect on the combustion, formation of chemical composition, and structure of combustion products. With an increase in the mass content of carbon in the initial mixture from 0 to 3.9 % the burning rate decreases by more than half, and the rate of dispersion of combustion products and the weight loss increase markedly. Under the action of overload, the two-phase melt of combustion products is stratified into two layers, which crystallize upon cooling. The lower metal layer contains Co, Nb, Cr, W, Mo, C, and impurity aluminum, and the upper layer contains mainly Al₂O₃. With an increase in carbon content above 4.0 %, the separation of the metal and oxide phases stops, and with a further increase, the flammability limit is reached. With an increase in carbon content in the mixture from 0 to 3.9 %, its concentration in the cast composite material reaches 5.4 %, the Al content is about 4.0 % and the content of Co, Nb, Cr, W, and Mo changes slightly. The combustion slag contains reducer metal oxide (Al₂O₃) and Cr₂O₃ impurity dissolved in it.

In this work, differential scanning calorimetry tests are performed on eutectic mixtures of 1-methyl-3,4,5-trinitropyrazole (MTNP) and 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF) with different molar ratios, phase diagrams of the melting temperature and composition and those of the melting enthalpy and composition are constructed. Then, the ratio of the lowest eutectic system is obtained on the basis of the phase diagrams, and the lowest eutectic mixture of MTNP/DNTF is characterized by energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric mass spectrometry, mechanical sensitivity test, and detonation performance calculation. The results show that the ratio of the lowest eutectic system of MTNP/DNTF is 70.3/29.7, and the melting point is 78.9 ^oC, which is very close to the melting point of TNT. Raw MTNP and raw DNTF can be uniformly mixed to form the lowest eutectic, and there is no chemical reaction between the raw materials, only a certain intermolecular force exists. The products of thermal decomposition are H₂O, NO, N₂O, and CO₂. The lowest eutectic mixture also has lower mechanical sensitivity and excellent detonation performance. Thus, the lowest eutectic mixture has a potential to replace molten cast TNT-based explosives, thereby meeting the demands of modern weapons and equipment.

An improved diffuse interface model is proposed to numerically simulate the interaction dynamics between solid explosive detonation and compressible inert materials. The chemical reaction of solid explosive detonation is simplified as the solid-phase reactant is converted into a gas-phase product. Thus, the mixture within a control volume is regarded to be composed of three kinds of components: solid-phase reactant, gas-phase product, and inert materials. Due to their differences in thermodynamic properties, three kinds of components can be thought to be in mechanical equilibrium and thermal nonequilibrium. The evolution equation for the volume fractions of all components is derived on the basis of the entropy production and pressure equality among the components. The evolution equation for the pressure of the mixture is also obtained and added to the diffuse interface model. Thus, the governing equations of the proposed diffuse interface model include the conservation equations for the mass of each component, the conservation equations for the momentum and total energy of the mixture, the evolution equation for the volume fraction of each component, and the evolution equation for the pressure of the mixture. The important characteristics of the proposed model are simultaneous consideration of mass transfer from the chemical reaction and heat exchange from thermal nonequilibrium and also direct calculation of the pressure from the governing equations. The proposed model owns thermodynamic consistency to effectively eliminate nonphysical oscillations near the material interface. Meanwhile, it can apply to arbitrary expressions of the equation of state, allow for any number of inert materials, and also treat large density ratios across the material interface.

In the present study, various test methods in the free field and confined explosions of cast HMX-based thermobaric explosives (TBX) and TNT are applied to quantify the explosion performance of TBX. The results show that the Mach reflection overpressure p and impulse I of TBX in the free field are much larger than those of TNT at the same relative distance from the explosion center. Based on the measured experimental data, semi-empirical formulas for calculating the overpressure at different distances from the TNT and TBX charges are derived. The fireball temperature and the duration of temperature higher than 1 500 ºC of TBX are seen to be significantly greater. The measured peak pressure of the two explosives blast in an explosion tank are compared with the values predicted by modified calculation models, and the results are in good agreement. In addition, the quasi-static pressure generated by TBX in the explosion tank is 30.9 % higher than that of TNT, which obviously reveals thermobaric effects of TBX. Based on the overpressure and quasi-static pressure calculation model, the TNT equivalents of TBX are calculated to correctly evaluate the TBX performance. The related contents in this paper will guide the formulation and performance assessment of TBX.

Results of experiments on loading flat samples of plasticized HMX by a shock wave are presented. Recording is carried out via an X-ray method in which X-ray is triggered by a sensor that responds to the onset of detonation in a sample. The time and place of the onset of detonation and the influence of the initial density of the sample on these parameters are determined. Experimental results are reproduced in finite element calculations. A dependence between the computational model parameters and the initial density of the sample is obtained.

An approximate theoretical analysis of a new method for testing explosive materials for sensitivity to mechanical stress, which is known as the crumbling shell method, has been carried out. In this non-impact method, the rupture of the shell releases the solid explosive material contained in it from the compressive load and allows it to free lateral expansion. In the process of high-speed flow, the substance explodes if the compressive stress is created large enough. The picture of the explosion as a whole seems to be similar to the phenomenon of initiation of an explosion when a charge of a solid explosive material is destroyed by an impact on a pile driver. Therefore, for the mathematical description of the test procedure under consideration, a previously developed model of the radial flow of a viscoplastic explosive material, its dissipative heating and thermal ignition in hot spots of the fluid is partially used. The data obtained on the change in various parameters during the initiation of an explosion make it possible to visualize its course not only within the framework of the method under consideration, but also to generalize them to explosion-like processes in a variety of materials that are suddenly released from a high load.

The reasons for the appearance of unstable large and small waves in the joint zone during explosion welding are investigated. Such waves arise when there are regions on the projected plate with even a small (10 ÷ 16 %), but abrupt (stepwise) change in thickness in the form of grooves obtained by machining. Unstable waves in the vicinity of the steps are formed only in the case when the width of the groove is greater than the thickness of the projectile plate. If the grooves are made on a fixed plate, then unstable waves do not arise. Analysis of the experimental data shows that the size of the waves generated in the bimetal in the vicinity of the steps on the thrown plate is affected by a sharp change in the impact angle associated with the bending of the plate at the places of the steps.