Home – Home – Jornals – Combustion, Explosion and Shock Waves 2016 number 3

The propagation of fuel-rich hydrogen-air flames with added ethanol has been studied using numerical methods. It has been shown that the inhibition by ethanol is less effective compared to propane and propylene. The addition of ethanol leads to the effect of superequilibrium temperatures, but it takes place only at ethanol concentrations above a certain value. At the flammability limit of fuel-rich mixtures of hydrogen, ethanol, and air, determined by the Le Chatelier rule, the estimated maximum flame temperature is constant. The exception is mixtures with a small addition of ethanol.

The combustion of ultrahigh molecular weight polyethylene (UHMWPE) in airflow perpendicular to the polyethylene surface (counterflow flame) was studied in detail. The burning rate of pressed samples of UHMWPE was measured. The structure of the UHMWPE-air counterflow flame was first determined by mass spectrometric sampling taking into account heavy products. The composition of the main pyrolysis products was investigated by mass spectrometry, and the composition of heavy hydrocarbons (C₇ – C₂₅) in products sampled from the flame at a distance of 0.8 mm from the UHMWPE surface was analyzed by gas-liquid chromatography mass-spectrometry. The temperature and concentration profiles of eight species (N₂, O₂, CO₂, CO, H₂O, C₃H₆, C₄H₆, and C₆H₆) and a hypothetical species with an average molecular weight of 258.7 g/mol, which simulates more than 50 C₇ – C₂₅ hydrocarbons were measured. The structure of the diffusion flame of the model mixture of decomposition products of UHMWPE in air counterflow was simulated using the OPPDIF code from the CHEMKIN II software package. The simulation results are in good agreement with experimental data on combustion of UHMWPE.

The paper describes the formation of the combustion zone structure of a titanium powder layer in inclined rectangular air channels with natural gas filtration. It is shown that heterogeneous combustion near the critical conditions of its existence with limited supply of gaseous reagent in the reaction zone and under the effect of gravitational forces is accompanied by rearrangement of the plane homogeneous front into more complex wave structures: cellular, cross-cellular, and heterogeneous. The features of the process under study is the presence of gaseous impurities affecting the gas exchange in the reaction zone, the destabilization of the plane front, and the formation and propagation of heterogeneous and cellular wave structures.

The method of obtaining combustion efficiency curves for fuel mixtures proposed by Annushkin is modified on the basis of data of high-altitude tests of high-velocity combustors integrated with the inlet. The combustion efficiency curve of a hydrocarbon-air mixture obtained in this study can be applied for design of high-velocity combustors.

Basic characteristics of combustion of the diesel fuel in a novel autonomous burner with injection of superheated steam into the combustion region are studied. The temperature distribution in the flame is obtained. Calorimetric measurements of heat release and gas analysis of combustion products are performed. The environmental effects of fuel combustion are compared for regimes with injection of a steam jet and an air jet. It is demonstrated that the combustion regime with steam gasification ensures high combustion intensity and combustion efficiency; moreover, the combustion process becomes more environmentally friendly.

Molecular dynamics simulations of melting of aluminum nanoparticles are performed with the use of the DL_POLY software package and embedded atom potential method for determining the thermal conductivity. Analytical approximations for the dependences of the thermal conductivity and specific heat on the temperature and particle size are reported. Based on the thermophysical parameters obtained in the study, the problem of nanoparticle melting is solved within the framework of the phenomenological approach.

This paper presents the experimental study of ignition and combustion of micro- and nanoparticles of aluminum diboride as part of pyrotechnic energy-saturated compositions in a gas generator with an air afterburner chamber and the thermodynamic calculations of combustion of pyrotechnic compositions based on aluminum diboride in air. The discharge of the combustion products from the afterburner chamber is recorded on video. It is shown that replacing micron aluminum diboride by powdered diboride with a mass-average diameter of particles equal to ≈270 nm in the pyrotechnic composition and increasing the pressure in the afterburner chamber cause the combustion efficiency in air to increase by 5–20%.

This paper describes a study on the burning of pressed and bulk-density samples from a Ni + Al mixture subjected to mechanical activation. It is shown that mechanical activation and dispersion have a different impact on the burning rate of the samples under study. The gas flow hardly changes the burning rate of the bulk-density mixtures. The linear burning rate of the dispersed bulk-density mixture is 1.7 times greater than that of the pressed mixture, and the mass burning rates are equal to each other. The calculations showed that the conductive heat transfer mechanism in the combustion wave of the dispersed bulk density mixture is the principal mechanism.

The thermal effect of the phase transition on unstable regimes of gasless combustion is numerically studied within the framework of the model of solid flame combustion of a cylindrical sample. The closer the phase transition temperature to the burning temperature, the more pronounced the effect of the phase transition on the combustion character. In this case, the combustion front surface is noticeably smoothed owing to reduction of temperature gradient values. A relationship between the change in the combustion modes considered in the study and the change in the phase transition parameters is found. An unsteady periodic symmetric mode of combustion with ring-shaped trajectories of motion of combustion sites over the side surface is obtained.

This paper presents the results of a numerical and experimental study of gasification of carbonaceous materials in the filtration combustion mode using mixtures of air with CO₂ as an oxidizer. The results obtained are compared with the results on gasification of carbonaceous materials by a steam-air mixture. It is shown that the replacement of steam in the gaseous oxidizer by an equal volume CO₂ leads to a marked reduction in the combustion temperature. The maximum calorific values of the product gas in coal gasification by a mixture of air and CO₂ are close to the values obtained for steam-air gasification.

Experiments aimed at studying the ignition of coal dust obtained by coal disintegration in high-energy mills are performed in a tubular furnace. Effective kinetic constants of ignition of coal dust ground in a vibrational-centrifugal mill and in a disintegration mill under conditions of rapid heating are determined for the first time. It is shown that the volatile release rate depends on the method of coal grinding.

This paper presents the results of an experimental determination of the width of the reaction zone in a detonation wave in nitromethane sensitized by diethylenetriamine. It was found that increasing the mass concentration of diethylenetriamine from 0 to 2.0% reduced the typical reaction time by a factor of less than two while the critical diameter decreased by an order of magnitude. This discrepancy is explained by the fact that the critical detonation diameter of neat nitromethane is determined not by the reaction time but by flow instability at the edge of the charge, manifested in the occurrence of a wave of reaction disruption. Increasing the initial rate of nitromethane decomposition by addition of diethylenetriamine leads to flow stabilization and thus to a change in the nature of the critical diameter.

To better understand the detonation characteristics of ammonium nitrate (AN) and activated additives mixtures, potassium chloride (KCl) and monoammonium phosphate (MAP) are mixed with AN by different mixing methods. The UN gap test and scanning electron microscopy are applied to study AN and AN-additive mixtures. For the mechanical mixing method, the detonation velocity of AN-additives decreases with increasing the additive proportion, while the detonation velocity of modified AN prepared by the solution mixing method shows the opposite tendency. It is proved that the sensitivity to shock waves increases as the size of AN particles decreases. The type of additives, the mixing methods, and the particle size distribution are important parameters that affect the detonation characteristics of AN.

An underwater explosion test is used to determine the detonation properties of metallized explosives containing aluminum and boron powders. An oxygen bomb calorimeter (PARR 6200 calorimeter, Parr Instrument Company, USA) is used to obtain the heat of combustion of the metal mixtures. As the content of boron powders is increased, the heat of combustion of the metal mixtures increases, and the combustion efficiency of boron decreases. The highest value of the combustion heat is 38.2181 MJ/kg, with the boron content of 40%. All metallized explosive compositions (RDX/Al/B/AP) have higher detonation energy (including higher shock wave energy and bubble energy) in water than the TNT charge. The highest total useful energy is 6.821 MJ/kg, with the boron content of 10%. It is 3.4% higher than the total energy of the RDX/Al/AP composition, and it is 2.1 times higher than the TNT equivalent.

The optical thermal radiation arising from the shock collapse of glass or polymer microballoons in a transparent condensed medium (water or polymerized epoxy resin) was detected. The temporal characteristics of the detected radiation in the pressure range 0.5–29 GPa at different viscosities of the material surrounding the pore were determined. The brightness temperature of hot spots was estimated to be 1600–3200 K at a pressure of 2–29 GPa. The length of the leading edge of the radiation pulse corresponding to the time of hot-spot formation increases from 2·10^–8 to 30·10^–8 s, depending on the shock-wave intensity and the viscosity of the material surrounding the pore. Analysis of the data shows that in the pressure range 5–29 GPa, hot-spot formation is dominated by the hydrodynamic mechanism of collapse and in the range 0.5–5 GPa, by the viscoplastic mechanism.

A pure emulsion based on an aqueous solution of ammonium nitrate placed in a steel tube 114 mm in inner diameter was shock loaded. The achieved dynamic pressure of 30 GPa, far exceeding the calculated detonation pressure, did not lead to the development of an explosive process.

The analysis of the dynamic response of a circular tunnel in three types of soil at different depths under surface detonation of a 250-kg TNT charge reveals that the tunnel peak particle velocity and the failure zone length are sensitive to the soil type and material properties. The buried tunnel in silty clay sand has the least damage; the length of the failure zone is 5 m in the longitudinal direction and 0 to 60^oC at the top arch.

Regimes of continuous spin detonation of two-phase kerosene-air mixtures with small addition of hydrogen are obtained for the first time in a flow-type annular cylindrical combustor 503 mm in diameter.