Home – Home – Jornals – Advanced Search

Results of studying stabilization of a homogeneous hydrogen-air flame on an optical discharge plasma in a high-velocity flow are reported. The main aspect of experiments is providing stable combustion behind the region of laser beam focusing without any mechanical flame holders. The laser radiation parameters are sufficient for creating a quasi-steady plasma in the flow. It is shown that the optical discharge stabilizes the flame front in a wide range of equivalence ratios for flow velocities up to u = 200 m/s. The laser radiation parameters within the range of their variation from one experiment to another exert a minor effect on the turbulent flame velocity. Flame stabilization behind the optical discharge region has some specific features. An important parameter is heat release due to hydrogen combustion. A dimensionless criterion is derived; the turbulent flame velocity is a linear function of this criterion.

Injection of inert particles into a stoichiometric hydrogen-air mixture with velocities ranging from 0.1 to 1.0 of the Chapman-Jouguet detonation velocity is calculated. Resultant flow regimes are analyzed. It is found that an increase in the particle temperature leads to ignition of the mixture, while an increase in the particle velocity leads to detonation wave initiation. Critical conditions of detonation initiation in terms of the particle concentration, particle size, and injection velocity are determined. Various possible scenarios of detonation initiation are demonstrated, depending on the particle diameter and concentration, including regimes with multiple initiation sites. Flow charts are constructed in the plane of the parameters “injection velocity, temperature of particles of various sizes”.

This paper first presents chemical time scale values measured by the PIV method for premixed methane-air and dimethyl ether-air flames depending on the equivalence ratio and the concentration of the inhibitor trimethyl phosphate at atmospheric pressure. Comparison of the experimental results with theoretical estimates made based on the Zeldovich-Barenblatt hypothesis shows their qualitative agreement. The chemical time scale within the accuracy of the experiment depended only on the burning rate, rapidly decreasing as it increases. At fuel-air flame speeds close to and above 0.6 m/s, the results of the experiments shown high accuracy of theoretical estimates based on the Zeldovich-Barenblatt hypothesis.

Heat and mass transfer processes and the rate of fuel oxidation are the determining parameters of combustion of pre-mixed fuel gas streams and an oxidizer and combustion of condensed fuels in a gaseous oxidizer. A correct description of these processes is of both scientific and practical interest. The influence of the kinetics of chemical reactions and diffusion of fuel molecules on the thermal and chemical structure of the flame forming around a polymethyl methacrylate (PMMA) sphere under f natural convection in the air has been studied by numerical simulation. The three-dimensional gas flow around the solid body was calculated on the basis of the system of full Navier-Stokes equations for a multicomponent mixture taking into account diffusion and heat exchange between the surface and gas, convection, and radiation heat transfer. The kinetic model represents conjugate reactions both on the surface of the condensed material and in the gas phase. The formation of gaseous fuel methyl methacrylate (MMA) on the surface is described by a one-step efficient PMMA pyrolysis reaction. The oxidation of MMA in the gas phase is described by the global reaction C₅H₈O₂ + 6O₂ → 5CO₂ + 4H₂O. It has been found that the temperature and flame species concentration profiles practically do not depend on the rate constant of this reaction provided that the characteristic reaction time is much less than the characteristic time of MMA diffusion. It has been shown that varying the diffusion coefficient of MMA has a significant effect on the thermal and chemical structure of the flame. An increase in the diffusion coefficient of MMA leads to an increase in the maximum flame temperature. The results of the study show that the transport properties of compounds required to calculate their transpot coefficients are one of the most important parameters for accurate CFD simulation.

The properties of azidoacetylene derivatives of s-triazine containing various combinations of propynyloxy, propynylamino, methylpropynylamino and azido groups have been studied, and their enthalpy of formation in the condensed phase, density, and impact and friction sensitivity have been determined. Based on these data, the energy parameters of the detonation, combustion, and adiabatic transformation of both individual compounds and their compositions with SKI-3 binding isoprene rubber have been calculated. The results of the integrated experimental and theoretical studies lead to the conclusion about the high calorific value of the investigated individual compounds and compositions based on them.

The ignition and combustion characteristics of a high-energy material containing ammonium perchlorate, butadiene rubber, and an ultrafine powder mixture of aluminum, titanium, or iron with amorphous boron are presented. An experimental testbed, a CO₂ laser, and a constant-pressure bomb are used to measure the ignition delay time and burning rate of the high-energy material while varying the heat flux density and pressure in the chamber. It is shown that replacing amorphous boron with ultrafine Al/B, Ti/B, or Fe/B in the material reduces the heating time and the moment of flame appearance on the propellant surface due to an increase in the reaction rate and a decrease in the oxidation temperature of these mixtures on the surface of the reaction layer. In this case, the burning rate of the high-energy materials with Me/B at excess pressures increases significantly (up to 240% for Al/B-HEM and up to 120% for Ti/B-HEM at a pressure of 5.0 MPa).

This paper presents combined metal oxide catalysts for the decomposition of ammonium perchlorate, combining two transition metal oxides (iron and cobalt) deposited on the surface of a carbon support. Combined catalysts are obtained by impregnation and chemical precipitation methods. Catalyst samples containing various phases of iron and cobalt oxides are obtained by varying the calcination temperature. The structural and morphological features of the synthesized catalysts are studied using XRD, SEM, and BET methods. As shown by the study performed using differential scanning calorimetry, the synthesized combination catalysts manifest high catalytic activity during the thermal decomposition of ammonium perchlorate, reducing the peak temperature of the high-temperature stage of decomposition by more than 60oC.

The authors analyze the influence of proppant parameter on the long-term conductivity of hydraulic fractures. Pressing of proppants in fracture walls and proppant smashing was studied using FCMS-V fracture conductivity system, field emission scanning electron microscope, polarization microscope and the sieve method. The correlations between the conductivity, grain size, grain-size composition, proppant concentration and placement technique, closure pressure of fractures and pressure of proppant pressing-in in the fracture walls are revealed. Pressing and smashing of proppant grains of different size under different closure pressure of fractures is discussed. The recommendations on proppant placement during hydraulic fracturing are given as a case study of methane recovery from coal seams in YC site of Ordos Basin in China.

The article presents the laboratory-scale studies on processibility of fine-grained old tailings at Kovdor GOK. Effect of collecting agents represented by fat tall oil acids (FTOA) is investigated. The froth flotation tests show high selectivity of agent Berol-2015 relative to apatite. From the lab-scale tests, it is found that with collector FTOA, the P₂O₅ content of concentrate is not higher than 24.4% despite a high degree of desliming of flotation feed (~ 70.0%). With collector Berol-2015, the concentrate content of P₂O₅ reaches 35.0-37.7% without preliminary desliming.

By means of determining the suspension effect, the authors studied the change in the surface properties of apatite under the action of reagents and ions present in flotation pulp during processing of apatite-bearing ore. It is shown that the ratio of acid-base centers of apatite surface change in interaction with ions HCO₃⁻ , CO₃^2- , HPO₄ ²⁻ , and oleate ions in distilled water and in water after deionization to remove carbon dioxide. The change in apatite surface properties in alkaline water shows up as quantitative superiority of base centers. Such ionization of mineral surface favors adsorption of cations, for example, Ca²⁺, and sets background for more efficient interaction between anion-type agents. The data obtained from the studies of the suspension effect, correlate with the results of infrared spectroscopy of apatite treated by the appropriate agents.