Vol 54, No 2 (2018)

The structure of premixed ethyl butanoate/O₂/Ar flames stabilized on a flat burner at atmospheric pressure was studied by molecular beam mass spectrometry. Mole fraction profiles of the reactants, stable products, and major intermediates and temperature profiles were obtained in flames of stoichiometric (φ = 1) and rich (φ = 1.5) combustible mixtures. Experimental data are analyzed and compared with previously obtained experimental and numerical data for methyl pentanoate flames. The structure of ethyl butanoate flames is simulated using a detailed literature chemical-kinetic mechanism for the oxidation of fatty acid esters. The experimental profiles are compared with the simulated ones, and the conversion pathways of ethyl butanoate are analyzed. Based on a comparative analysis of experimental and simulated data, the main shortcomings of the model presented in the literature are identified and possible ways are proposed to improve the model. The decomposition of ethyl butanoate and methyl pentanoate are discussed based on an analysis of their conversion pathways; similarities and characteristic differences between their oxidation processes due to the structural differences of the molecules of the fuels are outlined.

Bis(4-nitrofurazan-3-yl)furazan (DNTF) and 3,4-bis(4-nitrofurazan-3-yl)furoxan (DNFF) have been studied as potential components of composite solid rocket propellants. Their heats of combustion and enthalpies of formation have been determined experimentally. X-ray diffraction analysis has shown that the DNTF and DNFF crystals are orthogonal with the same space group P2₁2₁2₁. It has been found DNTF and DNFF are ineffective in rocket propellants with a hydrocarbon binder; however, when using DNTF for compositions without aluminum and with an active binder, it is easy to provide a specific impulse of 254.5 s at combustor and nozzle exit pressures of 40 and 1 atm, respectively, and at a density of 1.77 g/cm³, and when using DNFF, a specific impulse of 258 s at a density of 1.79 g/cm³.

The possibility of combustion of a mixture of chromium peroxide with aluminum nitride is shown experimentally. The effect of initial pressure of nitrogen and ratio of reagents on an average linear burning rate, as well as on a relative mass loss in the combustion of a CrO₃/AlN mixture is studied. The concentration limits of the burning rate of the test mixture are determined. The microstructure and phase and chemical compositions of the combustion products of the chromium–nitride-aluminum mixture are described.

This paper describes the development of a physico-mathematical model of spark ignition of a coal dust–air mixture, which is based on a two-phase two-speed model of reacting gas-dispersion medium. There are the results of numerical solution on the problem of spark ignition of a coal dust–air mixture with allowance for its movement caused by gas expansion during heating. The relationships between the minimal energy of spark ignition of a coal dust–air mixture and the mass concentration and particle size of coal dust are obtained. The particle size increases along with the minimal energy of spark ignition. There is mass concentration of coal dust particles with which the energy of spark ignition is minimal. The comparison of the results of calculations of the minimal energy of spark ignition of coal dust with known experimental data yields their satisfactory agreement.

Physicomathematical models are proposed to describe the processes of detonation propagation, attenuation, and suppression in hydrogen–oxygen, methane–oxygen, and silane–air mixtures with inert micro- and nanoparticles. Based on these models, the detonation velocity deficit is found as a function of the size and concentration of inert micro- and nanoparticles. Three types of detonation flows in gas suspensions of reacting gases and inert nanoparticles are observed: steady propagation of an attenuated detonation wave in the gas suspension, propagation of a galloping detonation wave near the flammability limit, and failure of the detonation process. The mechanisms of detonation suppression by microparticles and nanoparticles are found to be similar to each other. The essence of these mechanisms is decomposition of the detonation wave into an attenuated frozen shock wave and the front of ignition and combustion, which lags behind the shock wave. The concentration limits of detonation in the considered reacting gas mixtures with particles ranging from 10 nm to 1 μm in diameter are also comparable. It turns out that the detonation suppression efficiency does not increase after passing from microparticles to nanoparticles.

Experimental data on single and double shock compression of initially liquid and gaseous (compressed by initial pressure) hydrogen isotopes (protium and deuterium) at pressures of ≈10–180 GPa and temperatures of ≈3000–20 000 K are considered. The mean values of the measured variables (pressure, density, internal energy, and temperature) show that hydrogen at a pressure of ≈41 GPa in the temperature interval of ≈3500–5700 K and at a pressure of ≈74 GPa in the temperature interval of ≈5000–7500 K is characterized by a negative value of the Grüneisen coefficient. Such an anomaly may play a key role in some processes, including those proceeding in the Jupiter gas envelope, which mainly consists of protium (≈90%) and helium (≈10%). In the range of pressures (depths) of its manifestation, convection in the protium envelope is forbidden with an increase in temperature in the envelope with increasing pressure. Possibly, a comparatively low fraction of helium does not suppress the anomaly, and it serves as a barrier for large-scale convection in the Jupiter envelope. Additional refining experiments are required to confirm this anomaly.

Explosively welded metal plates are characterized by the formation of local microvolumes at the interlayer boundaries within which there is mixing of interacting materials. These microvolumes can be arranged discretely along wavy boundaries or continuously in the form of thin interlayers along planar boundaries. Based on the results of many published works, it has been shown that the material is melted in these zones, and its subsequent solidification occurs at a high rate leading to the formation of metastable phases. In this paper, the formation of metastable phases in steel–steel, Ta–steel, Nb–Al, and Zr–Cu joints is analyzed. The cooling rates of these materials in the mixing zones is estimated. Calculations show that the cooling rate of the melts formed in the weld zones of the investigated composites is in the range 10³–10⁶ K/s. Cooling of mixing zones at such high rates results in the formation of metastable structures. In some cases, the crystallization of materials is suppressed and metallic glasses and quasicrystalline phases are formed in the melt zones.