Home – Home – Jornals – Combustion, Explosion and Shock Waves 2025 number 4

Most interesting and important gas-dynamic and kinetic parameters of combustion, explosion and detonation of the combustible ammonia/oxygen system in the range from the lower to the upper concentration limit with a change in the initial pressure and temperature are presented. From the point of view of explosion safety, the most important data are on the critical initiation energy, which allows analyzing the relative danger of various mixtures. Critical energy is defined as the minimum energy of the initiator that ensures the propagation of combustion and detonation waves in the mixture under study: the lower the critical initiation energy, the more dangerous the mixture.

The paper presents the results of a study of the effect of methane dilution with hydrogen on the electrochemical properties of the flame. Both diffusion flames and combustion of a premixed mixture in a Bunsen burner were considered. It was found that for mixtures with a molar fraction of methane in the fuel of more than 40%, the electric current linearly depends on the amount of methane. When the molar fraction of methane in the mixture is less than 40%, the dependence becomes nonlinear. The transition boundary from linear to nonlinear relationship between the magnitude of the flowing current and the amount of methane in the fuel mixture does not depend on the flow rate, the shape of the electrodes, and the combustion mode (diffusion, premixed fuel-air mixture). Registration of the chemiluminescence of the CH* radical demonstrates a similar dependence of the flame glow intensity on the volume fraction of methane in the fuel.

The results of an experimental study of initiation of hydrogen combustion in a supersonic flow with fuel supply from the channel wall are presented. Data are obtained on the dynamics of disturbance development from gas-dynamic pulses and on the transition to the combustion mode in a pseudo-shock, when fuel is supplied from the combustion chamber walls rather than along the flow axis. Features of pre-detonation combustion initiation for such a scheme of hydrogen supply to a supersonic flow are revealed. It is shown that the steady-state modes of pre-detonation combustion slightly differ depending on the fuel supply method (along the axis or from the flow periphery), while the dynamics of wave structure propagation from gas-dynamic pulses is almost identical in both cases.

The paper presents the results of pyrolysis of tableted microparticles (1 g/cm³) of brown, long-flame gas, gas, fat and coke coals in an argon environment under the action of laser pulses (1064 nm, 12 ns, 6 Hz, 0.2 ÷ 0.5 J/cm²), which results in a number of nonlinear processes: 1) ablation of explosive samples with the emission of microparticles of 10 ÷ 60 μm in size upon reaching a radiation energy density of 0.1 ÷ 0.2 J/cm²; 2) optical breakdown localized on microprotrusions on the surface of coal particles, evaporation of microprotrusions and deposition of a thin film of amorphous carbon on the reactor walls; 3) initiation of thermochemical reactions in the breakdown channels, leading to the release of gaseous products, the concentration of which nonlinearly increases with an increase in the energy density of laser pulses. Molecular gases H₂, CH₄, C₂H₂, CO, CO₂ were registered. Dependences of the composition of gaseous products of coal pyrolysis on their technical and genetic characteristics were established.

The possibility of synthesizing metal ceramics from a powder and granulated mixture of (100 - X)(Ti + C) + XMe, X = 0 ÷ 30 % (wt.), was tested by replacing nichrome Me = X20H80 with a mixture of Ni and Cr metal powders for granules of 0.6 and 1.7 mm in size. The experiments were carried out with impurity gases filtered in the direction of the combustion front or removed through the side surface of the sample. Quantitative estimates of the impurity gas content in the studied mixtures were obtained, which satisfactorily explained the experimental combustion rate of the granulated mixtures. The calculation results showed that a safe conductive combustion mode was observed for all compositions with 0.6 mm granules. For a batch of 1.7 mm granules, combustion occurred in the convective mode at X < 10 % (a bundle of Ni and Cr) and at X < 20 % (a bundle of nichrome). The results of X-ray phase analysis showed the identity of the phase composition of combustion products when replacing nichrome powder with a mixture of Ni and Cr powders with the same dilution with a metal binder X and the absence of side phases.

The propagation of a detonation wave in narrow flat and square channels is numerically simulated. The processes of instability development of a plane detonation wave and formation of a non-stationary multi-front structure are studied, the features of this process in two-dimensional and three-dimensional cases are considered. It is shown that in a flat channel the growth of transverse disturbances leads to the formation of a cellular structure first with small, then with larger cells. In a square channel the so-called diagonal three-dimensional structure is formed, which, however, is eventually replaced by the spin detonation mode. Its characteristics are studied, the spin step value is estimated. Good agreement with the predictions of the acoustic theory is shown.

In a flow-through annular combustion chamber with a diameter of 503 mm, with a narrowed outlet section and profiling of the channel (installation of cavities at the beginning or end of the chamber), the modes of continuous multi-front detonation of kerosene with air heated to 800 K were implemented and investigated. It was shown that the installation of cavities increased the frequency of transverse waves. In the coordinates of the specific air consumption --- excess fuel coefficient, the region of implementation of detonation modes was determined. It was found that the existence of the continuous multi-front detonation mode is due to collisions of transverse shock waves generating transverse detonation waves, which degenerate into shock waves before collisions. When installing a cavern at the end of the annular cylindrical chamber, the maximum specific impulse relative to the fuel of 2,040 s was obtained. The minimum length of the combustion chamber in which the continuous multi-front detonation mode is implemented is in the range of 530 ÷ 670 mm. Measurements of pressure profile pulsation levels in the pre-chamber and at the combustion chamber outlet by high-frequency sensors have determined that they belong to the category of sound vibrations. This is important for the use of detonation combustion in practical applications.

The combustion of aluminum agglomerate particles with a diameter of 215 ÷ 840 μm in free fall in air at atmospheric pressure was investigated. Initially, spherically symmetric combustion is replaced by asymmetric combustion, fragmentation occurs; eventually, the combustion process ends with the formation of an oxide residue. The listed events are characterized by the corresponding time. In this article, the duration of the symmetric combustion stage is determined --- on average 0.5 ± 0.1 in relation to the combustion time. Empirical approximating dependences of the coordinate and velocity on time (x(t) and v(t)) for particles of different diameters are obtained. To perform analytical calculations of the motion of burning particles, the viscosity of air in the vicinity of the particle was chosen to be 6.98 10^-5 Pa · s, which corresponds to an average temperature of 2,005 K. By comparing the empirical and calculated dependencies x(t) and v(t), the effective aerodynamic drag coefficient of the particle was determined depending on its size in the form C_d(D, Re) = (9.33 + 0.13 D)/Re, where Re is the Reynolds number from the range 0.2 < Re < 5.2. For estimated calculations, C_d = 77/Re can be taken.

The energy capabilities of a hypothetical zwitterionic nitrohydrazine H₃N⁺N^-NO₂ as a component of artillery propellants are assessed. Compositions with a hydrocarbon binder, compared to standard propellant charges, allow increasing the muzzle energy of a projectile by ≈33% for a 152-mm howitzer and by ≈27% for a 125-mm tank gun without increasing the temperature of the propellant gases. For a 120-mm mortar, the increase in the muzzle energy of a mine is ≈14%. Similar compositions based on ammonium dinitramide are considered for comparison, which have shown lower efficiency. Compositions with an active binder also achieve high performance indicators. However, they have a high temperature of combustion products, which is unacceptable for most barrel systems.

TNT has several disadvantages, such as high vapor pressure, toxicity and viscosity. Explosives free from these disadvantages are being sought. In this paper, a new explosive, TNBA, 2,4,6-trinitro-3-bromoanisole, is synthesized by a chemical method. The thermal decomposition characteristics of TNBA are tested by DSC/TG-MS. The mechanical sensitivity, thermal sensitivity and detonation characteristics of TNBA and cast explosive based on it are estimated. The results show that the measured density of TNBA is 1.871 g/cm³. At a heating rate of 10 °C/min, the thermal decomposition peak of TNBA is observed at 287 °C, and H₂, C, CH₄, H₂O, CO, N₂, CO₂ and HBr gases are released. The peaks of CO and N₂ are the strongest. These results are similar to those calculated using NASA CEA2 software. The thermal sensitivity of TNBA is lower than that of TNT. The detonation velocity and heat of explosion of TNBA and TNBA-based cast explosive are similar to those of TNT. In particular, TNBA and its cast explosive have advantages in chemical energy reserve, performance, brisance, and the ability to accelerate metals.

Using high-frequency pressure sensors Kulite XTEH-10L-190 (M) Series, pressure profiles were recorded in a transverse detonation wave propagating in an annular cylindrical chamber during continuous spin detonation of a hydrogen--air mixture. The pressure levels in the detonation wave front, in the air collector, and at the chamber outlet were determined in relation to the average static pressure recorded by low-frequency sensors (10 kHz) from <<Trafag>>. Pressure oscillations behind the wave front indicate complex gas dynamics of the processes in its vicinity. A region of chemical reaction was revealed behind the wave front, comprising about 6.3% of the period between waves. A decrease in the minimum excess fuel coefficient was found with an increase in pressure in the combustion chamber to 0.22, at which continuous spin detonation develops. The velocities of transverse detonation waves decrease with decreasing fuel-excess ratio and in some modes approach the ideal Chapman-Jouguet detonation velocity. Based on the total and static pressure readings at the combustion chamber outlet, the specific impulse is calculated, the maximum value of which, minus cold outflow, is 5,000 s at a fuel-excess ratio of 0.35. It is shown that the total pressure loss during air outflow from the manifold into the combustion chamber through a 6 mm wide gap (critical outflow mode) is 4 ÷ 5% higher than during subcritical outflow through a 10 mm gap.

The effect of aluminum powder distribution on the explosion energy of layered composite charges of thermobaric explosives based on a melt of high-energy 3,4-dinitrofurosan furoxan (DNFT) was investigated. The composites consisted of inner and outer cylindrical layers with controlled spatial distribution of aluminum powder. Blast tests were carried out in a closed explosion chamber filled separately with either nitrogen or air. Data were obtained on the quasi-static pressure, excess pressure in the shock wave, and the evolution of the fireball. Using numerical modeling, the diffusion of aluminum powder during the explosion was studied using a combined discrete element and finite element method. The results show that concentrating aluminum powder in the outer layer of the composite increases the concentration of aluminum powder in the cloud, which leads to an increase in the burning rate and energy yield in the early stages of the explosion. Conversely, aluminum powder concentrated in the inner layer is compressed toward the center and then bounces back, slowing down diffusion and affecting anaerobic combustion processes.