Home – Home – Jornals – Combustion, Explosion and Shock Waves 2024 number 2

A three-dimensional model for a burner is established, and effects of gas nozzle structural parameters on the combustion performance of the burner are studied. With a change in parameters, the reverse flow zone in the furnace changes obviously. The interaction and symmetry of the four reverse zones directly affect the flame stability. The change in the maximum and average temperatures in the furnace is not the main reason for the increase in NO_x emissions at the furnace outlet (M_NO). Most probably, the increase in M_NO is caused by the characteristics of the high-temperature area. In ten cases studied, the NO_x emissions are all lower than 30 mg/m³ and even lower than 10 mg/m³ in some cases (under normal conditions), which indicates that the ultra-low nitrogen emission of the boiler can be achieved by reasonably modifying the nozzle structure

Propylene oxide (C₃H₆O) is an intermediate product of oxidation of heavy hydrocarbons and can be used as an additive to conventional fuels to reduce soot emissions. New experimental data on the oxidation of C₃H₆O at low temperatures were obtained using an isothermal jet-stirred reactor. Experiments were carried out at temperatures of 600-1300 K and a pressure of 1 atm, and the residence time of the gas mixture in the reaction vessel was 1 s. Five detailed chemical kinetic mechanisms taken from the literature were tested. A mechanism that has the best predictive ability at low temperatures was identified. The mechanisms were also tested against experimental data on the structure of C₃H₆O flames. It has been found that at the moment there is no model that can correctly describe the combustion and oxidation of C₃H₆O at both low and high temperatures.

An economical method for numerical simulation of natural excitation of gas vibrations in low-emission combustors of gas turbine units has been developed and tested. The method is based on the use of the SAS SST k-ω turbulence model and the turbulent combustion model with a modified equation for a variable degree of combustion completion. To model the natural excitation of gas vibrations, a factor associated with gas pressure pulsations is introduced into the source term of this equation. Isolation of one of the modes of gas vibrations prone to natural excitation is carried out using a resonant filter operating in each cell of the computational domain. The results of the computational study obtained using the proposed method make it possible to study the influence of design measures and operating parameters of natural vibrations and to approach more rationally the choice of measures to suppress them.

The effect of heat loss on the possibility of implementing the most effective gas-phase combustion mode of a single boron particle in air at various initial temperatures and pressures of the oxidizing medium is analyzed analytically, taking into account the possible entry of the particle into the air environment, the temperature of which is lower than the melting point of boron, after its ignition and reaching a stationary gas-phase mode combustion. A method for calculating the maximum initial air temperature below which cooling and extinguishing of a burning boron particle occurs has been developed, and the boundaries of the regions of its gas-phase combustion and extinguishing have been determined. It has been established that when a single boron particle burning in a gas-phase mode enters air with a temperature below the melting point, the main factor determining the mechanism of its combustion is the air temperature, depending on which either the continuation of combustion of the particle in the gas-phase mode or its cooling takes place and changing the combustion mode to heterogeneous.

The total and radiant heat fluxes from a flame onto the surface of a solid fuel (polymethylmethacrylate) in the combustion zone for horizontal flame spread over the fuel surface were first quantitatively measured using two water-cooled miniature sensors with dimensions of 2.3 × 2.3 mm mounted inside the plate. A water cooling design for 2 × 2 × 0.5 mm sensors (greenTEG AG) has been developed that makes it possible to place them directly in the combustion zone. Radiant heat flux was measured by a sensor with a protective window made of ZnSe, and the total heat flux was measured by a similar sensor without protective window. The conductive heat flux determined using sensors was compared with that calculated from polymethylmethacrylate flame temperature measurements with thin thermocouples. The maximum radiant and total heat fluxes from the flame to the surface of polymethyl methacrylate measured using thermal sensors were 30-35 and 70-75 kW/m², respectively.

Regimes of detonation burning of a two-phase mixture consisting of TS-1 aviation kerosene and air in a radial vortex chamber 500 mm in diameter with exhaustion toward the center and geometry variations at the combustor entrance and exit are obtained and studied. Air is injected into the combustor through a vortex injector, and kerosene purged with air was injected through oppositely directed channels. Optical registration of the process was performed through transparent windows in the combustor by a high-speed camera with a frequency of 420000 frames per second. The flow pattern observed in the combustor with a free exit and an expanding nozzle is continuous spin detonation with one detonation wave rotating with a velocity of 1.68-2.17 km/s close to the Chapman-Jouguet detonation velocity or pulsed detonation with radial waves with a frequency of 0.14-0.26 kHz. Mounting of radial partitions yields pulsed detonation or combustion. In continuous spin detonation, the air flow rate is 3.6-11.7 kg/s, the kerosene flow rate is 0.2-0.77 kg/s, and the equivalence ratio varies from 0.63 to 2.5.

A superfine microcrystalline powder of bis-(triaminoguanidinium)-5,5'-azotetrazolate (TAGzT) is prepared by the high-energy ball milling method. The microstructure, elemental composition, thermal decomposition mechanism, and sensitivity characteristics of fine TAGzT are studied by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), thermal gravimetric and mass spectrometry, and sensitivity tests. The results show that fine TAGzT consists of irregular granules with a rough surface and contains only C and H elements. TAGzT begins to decompose at about 199 °C, with the thermal decomposition products being mainly CH₄, NH₃, and H₂O. The sensitivity test shows that fine TAGzT has good stability. As calculated by the EXPLO-5 software, fine TAGzT has better energy performance than HMX. Composite modified double base propellant (CMDB) samples containing fine TAGzT are designed and prepared. The microstructure, elemental distribution, thermal decomposition mechanism, and sensitivity characteristics of CMDB propellant samples are studied by SEM, EDS, XPS, DSC, and mechanical sensitivity tests. The results show that there are tiny bulges and cracks on the sample surface, and the mass ratio of the components is consistent before and after preparation. With an increase in the fine TAGzT content in the propellant, the thermal decomposition peak temperature moves backward, while E_K increases first and then decreases. The H₅₀ value of the CMDB propellant decreases with an increase in the fine TAGzT content. The CMDB propellants are calculated using the CproPEP software, where fine TAGzT is added to the propellant formulation to have higher values of I_sp and C* than those of HMX and lower values of T_c and M_c. By introducing fine TAGzT into the CMDB propellant, higher energy and better safety can be obtained

This study is aimed at investigating the mechanism by which a reactive material enhances the energy output of a composite charge consisting of an inner explosive, an intermediate non-detonating layer, and an outer explosive, which are widely used in tunable ammunition. Explosion experiments are conducted in two initiation modes. Using reactive Al/rubber significantly increases the fireball growth, shock wave velocity, and shock wave overpressure of the composite charge compared to using inert LiF/rubber. For simultaneous initiation, the increase is more obvious owing to the continuous exothermic reaction of the reactive layer. A composite charge with 40% (vol.) Al shows the highest difference in peak overpressure under the two initiation modes: 41.4%. A charge with 60% (vol.) Al ensures even lower shock wave and fireball velocities and peak overpressure than those of the 40% (vol.) Al charge, indicating that the excessive reactive Al content in the non-detonating layer inhibits the blast of the composite charge.

The relationship between the critical detonation thickness in transverse wedges made of plasticized TATB and the acoustic rigidity of the adjacent material and the speed of sound in it was determined by streak photography. The wedge-shaped charge was initiated over the entire lateral surface of the detonation wave propagating in a steady mode.

The process of detonation propagation in a charge made of a plasticized explosive composition based on TATB in the form of a hollow cylinder with a steel shell inside is studied when normal detonation is initiated along a line on the outer surface of the charge. In experiments, the shape of the detonation wave (DW) front at certain points in time was determined using the X-ray method. Using electric contact sensors, the speed of propagation of the DW front along the outer surface of the charge was measured. The original setup of the experiments made it possible to study the propagation of detonation at angles greater than 180 °C from the initiation line. It is shown that in the initiation plane the front velocity of the diverging DW is ≈7.3 km/s. In the region of the “shadow” of the initiation point, the speed of the front of the diverging DW decreases depending on the distance traveled both along the outer surface of the charge - up to ≈6 km/s, and along the inner - up to ≈5.6 km/s. At the same time, near the steel shell in the region of rotation angles of the DW front from approximately 150 to 210 °C, a zone of unreacted TATB was recorded, which may indicate the disruption of detonation and its transformation into a shock wave. A numerical simulation of the process was carried out using the SURF detonation kinetics implemented in the MIMOSA technique. The calculation results are in good agreement with experimental data both at the early stage of the detonation initiation process and in the region of the “shadow” of the initiation point, where the velocity of the DW front decreases.

A semi-empirical equation of state for bismuth has been constructed taking into account five solid phases, liquid, evaporation, and thermal ionization. The results of model calculations are in satisfactory agreement with data from static and dynamic experiments in the pressure range from atmospheric to ≈1 TPa and temperatures from room to ≈10⁵ K.

Periclase (MgO) is one of the important materials that make up the mantles of the terrestrial planets. In this regard, its properties at high temperatures and pressures reflect the nature of the planetary interior. Numerical modeling of shock wave loading of MgO taking into account the polymorphic phase transition in a pressure range of 325 ÷ 400 GPa was carried out using a thermodynamic equilibrium model. The parameters of the consistent equation of state for the high and low pressure phases of periclase (MgO I and MgO II) are determined. The thermodynamic parameters of these phases were modeled. Shock adiabats of single and double compression were constructed in the range 1 ÷ 1000 GPa, the values of heat capacity along the normal isobar, entropy as a function of temperature, and temperature along the shock adiabat were calculated. The modeling results were verified based on the results of experiments and calculations of other authors.

The paper is a summаry of experimental studies of water droplet breakup in the flow behind the shock wave in the range of gas flow velocities 40 ≤ U ≤ 175 m/s. A change between two different mechanisms of stalling breakup of the droplet occurs in this range of velocities, with domination of the inertia force in the case of droplet deformation and viscous friction force in the case of boundary layer shedding. The analysis of the change in the breakup mechanisms is based on a vast pool of observations and quantitative data on droplet dynamics and delays of its breakup obtained by a high-speed method of visualization with a stroboscopic laser source of light. A physical model of the process is constructed on the basis of experimental data and results of the parametric analysis, and criteria of the change in stalling mechanisms of droplet breakup are derived.