Home – Home – Jornals – Combustion, Explosion and Shock Waves 2020 number 6

The heat of combustion and the enthalpy of formation of 7,7'-bis(terfurazan [3,4- b :3,4'-d:3'',4''- f ]azepine (I) and 1,1'-dioxide-7,7'-bis (terfurazan [3,4- b :3,4'- d :3'',4''- f ]azepine (II), were experimentally determined. Product I was studied by X-ray diffraction analysis, and its crystallographic characteristics were determined. The efficiency of using compounds I and II as components of solid composite propellant was analyzed, and it was found in what type of compositions they are more effective than HMX.

Combustion of vapors of a flammable liquid whose temperature is below the flash point is under study. In this case, the flame propagates along the surface of the liquid due to being heated by combustion products. The velocities of an oxidizer moving toward the flame and propagating at velocities comparable to the normal velocity of premixed hydrocarbon flames are measured. The measurements show that the gas flow is laminar. There is a correlation established between the flash point of a flammable liquid and the flame propagation velocity. On the basis of the data obtained, it is assumed that the main mechanism of formation of a combustible mixture ahead of the combustion front is a diffusion mechanism.

In this paper, the so-called REDIM-DTF sub-grid scale combustion model is proposed to improve the well-known dynamically thickened flame (DTF) combustion model by combining the DTF modeling strategy with the reaction-diffusion manifold (REDIM) chemistry table, which is generated from a detailed reaction mechanism. The new model is then used to calculate two lean premixed swirling flames in the PRECCINSTA combustor via large eddy simulation. The radial profiles of velocity, temperature, and species concentration, as well as the flame surface area and vortex structure are analyzed. The results are in good overall agreement with the corresponding experiment, and the performance of the REDIM-DTF model is very similar to that of the DTF model. The predicted CO mass fraction profiles, however, show a relatively larger discrepancy between the original DTF model and the proposed REDIM-DTF model, which is thought to be due to different reaction mechanisms used. As a smaller number of species transport equations are solved in the REDIM-DTF model, its computational efficiency is about 15 % higher than that of the original DTF model.

The structure and phase composition of a material obtained via SHS in the combustion of a 87 % Ti + 13 % B powder mixture with the addition of Si₃N₄ is under study. The phase formation mechanism in this system is discussed. It is established that the material contains 64 % of the TiB phase with an orthorhombic structure and 36 % of the solid boron solution in titanium (α -Ti[T]). The boron content in α -Ti significantly exceeds its equilibrium content according to a state diagram. In the case of combustion of an 87 % Ti + 13 % B mixture with the addition of 5 % Si₃N₄, the finite product contains TiB, α -Ti[B], TiB₂, and Ti₅Si₃ phase. The TiB phase is present in the form of two modifications: orthorhombic and cubic. The completeness of a structural transition of the cubic modification of TiB into an orthorhombic one is determined by the cooling rate of a sample. It is assumed that the combustion of the mixture with the addition of Si₃N₄ forms the dispersed discharges of TiN, which are the crystallization centers of cubic TiB.

Data on the most important combustion and detonation parameters, such as wave velocities, pressures and temperatures of products, specific energy release of mixtures are presented for saturated C _n H_{2 n +2} (from methane ( n = 1) to eicosane ( n = 20)) and unsaturated C _n H_{2 n} (from ethylene ( n = 2) to eicosene ( n = 20)) hydrocarbons, methanol and ethanol as the main components of biofuels, and monofuels as a source of bifurcation structures of multifrontal detonation. Data are also given on on the critical initiation energies as a measure of the explosion hazard of combustible systems: the lower the energy, the more dangerous the mixture. Data were obtained for mixtures of each individual hydrocarbon with oxygen and air in a wide range of initial parameters: pressure, temperature, concentration and phase state of fuel components.

The combustion, explosion, and detonation in hybrid systems containing gas mixtures of CH₄/Air, CH₄/O₂, and O₂ with bituminous coal particles up to 200 μm in size with an average volume density of up to 700 g/m³ were studied on a vertical shock tube. X-ray diffraction patterns of the initial coal powder and coal samples subjected to high-temperature waves were analyzed. Data were obtained on the structure and parameters of waves in hybrid mixtures and in the same gas mixtures without coal dust. It is shown that in hybrid systems, coal dust has a weaker effect on the parameters of combustion and detonation waves than methane and methane in these waves is more reactive than coal dust.

Regimes of continuous spin detonation and continuous multifront detonation of a gas-droplet mixture of gaseous hydrogen and liquid oxygen in a plane-radial combustor (inner diameter of 100 mm and outer diameter of 300 or 200 mm) with exhaustion toward the periphery are obtained for the first time. The detonation front height of the gas-droplet mixture is greater than that of the gas mixture, which is caused by the critical size of detonation existence. Centrifugal forces acting on the products behind the detonation wave front favor faster filling of the plane-radial combustor with the fresh mixture and increase the detonation front height.

A flake aluminum powder (F-Al) is prepared by a bi-directional rotation mill method using a spherical aluminum powder (S-Al) as a raw material. Then, these two kinds of aluminum powders are used to prepare ammonium perchlorate-based composite modified double-base (AP-based CMDB) propellants. The properties of two kinds of AP-based CMDB propellants, such as the thermal decomposition performance, mechanical sensitivity, and combustion performance, are comprehensively researched. The results show that the exothermic peak temperature of the F-Al-AP-based CMDB propellant is lower than that of the S-Al-AP-based CMDB propellant. The impact and friction sensitivities of the propellant decrease by 12 % and 187 % after using F-Al to replace S-Al. In addition, the burning rate of the F-Al-AP-based CMDB propellant is 5.5 % higher.

HMX can be detonated by an exploding bridgewire (EBW) or a slapper. Direct HMX detonation by an electrical arc has not been demonstrated. This paper shows that the shock from a 99 % worst-case lightning current (200 kA and 500 ns rise time) can detonate standard-density HMX at elevated temperatures (i.e., HMX in the most sensitive d-phase at a temperature above 177^oC) and that the shock from a 200-kA peak current pulse with a 100 ns rise time can detonate HMX at ambient temperatures. Two necessary detonation conditions are used for these assertions. The relevant Pop-Plot for HMX is converted into an empirical detonation criterion, which is applicable to explosives subject to shocks of variable pressure. The minimum detonation spot size for detonation reported in the literature is used as the other condition. PBX-9501 and LX-04 have similar Pop-Plots to those of HMX; thus, the HMX result is directly applicable. Although PBX-9404 and PBX-9407 are HMX-based, they have somewhat lower Pop-Plot pressures than HMX and are more sensitive to shocks caused by electrical arcs than HMX. As the HMX thermal conductivity is low and the phase transition can be slow, the chance of having a sufficient amount of HMX converted to d-HMX during an accident is small; therefore, the threat of lightning shock-detonating HMX is very low. We recommend lightning simulation tests to be conducted for d-HMX. We also would like to point out that a lightning can ignite HMX, which, in turn, leads to detonation via the deflagration-to-detonation transition.

When studying the structure of the reaction zone in detonation waves of powerful explosives, one usually measures the mechanical characteristics of the flow - the distributions of particle velocity, pressure or density. Experience shows that on such profiles, it is rather difficult to distinguish the chemical reaction zone. These distributions, as a rule, are distorted when the flow interacts with measuring units. In this paper, we consider the prospects of an alternative method of electrical conductivity, which is largely free from the indicated disadvantages and has a number of advantages. The correlation between the region of high electrical conductivity and the reaction zone is substantiated by comparing the results of traditional methods and conductivity profiles.

The detonation of mixtures of highly dispersed PETN with sodium bicarbonate with a mass fraction of the latter up to 90 % is investigated using radio-interferometric and electron-optical (NANOGATE-22) methods along with a method using a PVDF pressure sensor. The experimental results obtained indicate the possibility of the existence of various detonation regimes in mixtures. If the mass fraction of NaHCO₃ ≤ 85 %, the detonation wave propagation is mainly due to shock compression. At a higher NaHCO₃ content (90 %), the jets of explosion products predominantly serve as propagation agents.

Large explosion-proof chambers are manufactured using cylindrical shells made of sheet metal by rolling and welding with addition of longitudinal and circumferential seams. In this case, one should make a choice of steel with increased strength or ductility. In this regard, this work presents the results of a study of the reaction of such shells made of 09G2S AND 10KhSND steel to dynamic loading.

Based on advanced numerical simulation technologies, such as the birth and death of element technique, large displacement technique, and fluid-solid coupling mechanism, and combined with the strain rate effect of concrete and steel materials, a complicated finite element model of a TNT-air-slab system is set up using the nonlinear explicit dynamic finite element analysis software LS-DYNA. A series of numerical simulation analyses is conducted on the reinforced concrete slab to evaluate the properties of the blast shock wave at the back of the slab. First, the typical characteristics of the blast shock waves at the front and back of the slab are described concisely. Then, the relation between the incident wave and the reflected wave is built by further studying the influence of the slab on the properties of the reflected wave at the front of the slab. And then, the relation between the reflected wave and the reformed wave is established by analyzing the effect of the slab on the change law of the reformed wave at the back of the slab. Finally, the basic steps for predicting the properties of the reformed wave are given considering the effect of the reinforced concrete slab on it. In addition, the case study demonstrates that the predicted results are true and reliable, and it indicates that the proposed method can accurately and effectively predict the properties of the reformed wave at the back of the reinforced concrete slab.

A new characteristic of detonating explosives is proposed - a chemical peak deceleration curve. An example of plotting such a curve on the basis of experimental data of the All-Russian Scientific Research Institute of Technical Physics for detonating plasticized TATB is given.