Home – Home – Jornals – Combustion, Explosion and Shock Waves 2002 number 4

Combustion of fog consisting of a hydrogen

The effect of thermal expansion on the minimum energy of gas spark ignition is studied using a mathematical model of spark ignition. It is shown that the thermodiffusion model of gas spark ignition underestimates the minimum spark energy by more than a factor of two. The dependence of the minimum spark ignition energy on the Damköhler number is studied, which characterizes the ratio of the flame propagation velocity to the speed of sound in a gas.
Key words: fuel gas, spark, thermal expansion, minimum spark energy.

The effect of vortex formation and the role of mixture flow rate in the excitation and sustenance of the self-oscillatory combustion regime of a kinetic singeing flame was studied experimentally. Using holographic interferometry and the Mies dispersion method, it is found that in the boundary layer at the burner exit, vortices arise periodically, which interact with the flame front to change the flame surface area and the heat release rate. It is shown that the main feedback mechanism is periodic vortex formation, and the occurrence of concentration regions of excitation and silence is related to the change in the number of waves falling on the flame height. It is found that in combustion of oxygen-rich fuel-air mixtures, acoustic oscillations arise at higher harmonics. .

A review of literature data is presented on experimental and theoretical investigations of carbon and solid-fuel gasification in various gas media at high temperatures (up to 1373 K). Methods of experimental and theoretical investigations are described. A theoretical formulation of the problem of nonstationary gasification of carbon is presented. The value of the real kinetic constant of carbon gasification by carbon dioxide is given.
Key words: carbon, carbon dioxide, active areas, nonstationary gasification, kinetic constant.

An approximate mathematical model is constructed and characteristics are calculated of ignition of a reactive plane infinite obstacle by a high-temperature nonstationary axisymmetric supersonic jet of combustion products escaping from the igniter. The approximate model data are compared with the results of numerical calculations using the system of equations of motion of an ideal gas, nonstationary equations of heat conduction and chemical kinetics, and conditions of conjugate heat exchange at the "gas

It is shown that the qualitative behavior of combustible porous substances under conditions of forced filtration can be principally different: self-accelerating explosionlike increase in temperature (ignition) or smooth increase in heating without noticeable specific features. Sets of parameters determining the type of behavior are determined. The critical flow rate of the gas is calculated as a function of the layer thickness. Induction periods are determined.
Key words: ignition, filtration combustion, induction period, mathematical simulation.

An experimental method for studying the combustion of porous specimens under non-one-dimensional filtration of a gaseous reagent is proposed. Propagation of a surface-combustion moving normally to the gas-permeable lateral surface of a specimen was observed in situ for the first time. When the surface fronts meet at the center of the specimen, the temperature increases, which explains previous experimental results.

Investigation was performed of the effect of sample density and the diameter of a coaxial hole in Ti + B based cylindrical samples on combustion rate, relative elongation, and the macrostructure of the products formed. The mechanism of samples fracture due to excess pressure of impurity gases is proposed. It is shown that on parametric diagrams "density

The paper reports a solution of the inverse and direct problems of high-temperature synthesis of intermetallide Ni₃Al by thermal shock. The results obtained are necessary for predicting the kinetics of high-temperature synthesis of intermetallide Ni₃Al and its melts.

Mathematical simulation of the structure of metallized heterogeneous condensed mixtures is performed. Evolution of a system of aluminum particles is studied in the case a heat wave passes over the mixture. It is shown that rapid heating of a heterogeneous condensed mixture forms a system of "clusters" of contacting aluminum particles, which may sinter to form a porous system that melts and disperses into individual droplets with further heating under the action of surface-tension forces. After coalescence, these droplets form agglomerates. The structure of "clusters" of contacting particles is studied, and the mean-mass size of metal particles is determined as a function of dispersion of the components and their concentration in the heterogeneous condensed mixture. It is shown that contacting aluminum particles in the heterogeneous condensed mixture form fractal-like structures, which may play a significant role in the course of combustion of the mixture.

The reaction mechanism and kinetics of self-propagating high-temperature synthesis in a Ti₅Si₃ system are experimentally studied. The Langmuir probe and optical spectroscopy are used to determine the composition and degree of ionization of the gas phase formed due to the combustion-induced degassing of impurities. The propagation of the combustion wave is shown to be accompanied by ionization of released gases, both the ion concentrations and electron temperatures being determined. Through a comparison between the data obtained and spectroscopic data, the ion species are identified.

Investigation was performed of the effect of an external electric field on the completeness of combustion of ASD-1 aluminum powder in an airflow and on the disperse composition of condensed combustion products. It is established that for an oxidizer-to-fuel ratio of 0.8 and a combustor inlet flow rate of 10 m/sec, the application of an electric field increases the completeness of aluminum combustion from 43 to 75%. In this case, the sizes of submicron particles of aluminum oxide practically do not change, and the mass average sizes and the mass concentration of the 4÷50 μm fraction decrease, due to the activating effect of the electric field on the vapor-phase combustion of aluminum particles. A decrease of the mass concentration of the size fraction larger than 50 μm from 12 to 3% under the action of the electric field suppress markedly the agglomeration of aluminum particles during combustion in air.

The paper describes a method for measuring the delay of combustion wave propagation through an obstacle and other heat-transfer parameters by continuous recording of electrical signals arising in a burning condensed system. This method is suitable for systems and obstacles that have marked electric conductivity. Results of investigation of combustion wave propagation through a tantalum obstacle in the 3Zr + 2WO₃ system using the proposed method are presented.
Key words: gas-free system, combustion, mechanical strains, obstacle, combustion e.m.f., heat transfer, thermal parameters.

Some performance of a number of emulsion explosives containing glass micro-baloons were studied experimentally and theoretically. For each of the explosives, detonation velocity was measured and calculated and ballistic mortar tests and cylinder expansion tests were carried out. The results obtained enables a comparison of the usefulness of both testing methods. The influence of some metal nitrates contained in the emulsion matrix on the performance and detonation parameters of the explosives was examined.

An original photograph of a retonation wave is presented; the wave arose spontaneously in a charge of a 20/80 nitroglycerine/ammonium nitrate mixture with a density of 0.9 g/cm³ at a distance of 0.8 of the charge length and went back half of the charge length toward the place of initiation. The velocity of the forward wave was 2300 m/sec, and the velocity of the retonation wave was 1700 m/sec. The retonation wave was registered only in one, unique experiment.
Key words: initiation, detonation, retonation wave, velocity, nitroglycerine, ammonium nitrate.

The microstructure, deformation characteristics, and electric conductivity of composites produced by explosive compaction of a copper–molybdenum powder mixture were studied. It is shown that an increase in detonation velocity during explosive treatment leads to an increase in crystal lattice microstrains and dispersivity of the block structure. This favors the plastic deformation of the particles, mainly copper particles, activation and weldability of their boundaries, which increases the conductivity of the compacts produced. Optimal conditions of explosive compaction and heat treatment for production of composites with high conductivity are found.
Key words: powder mixture, planetary mill, explosive compaction, heat treatment, electric conductivity, x-ray structural analysis.

An explosive method for producing ultrafine α-Al₂O₃ is developed and optimal synthesis parameters are determined. Particles of ultrafine α-Al₂O₃ have a spherical shape and are separated from one another. The size distribution is log-normal (number-averaged size 70 nm and variance 1.9). Special features of phase transitions in ultrafine aluminum oxide under shock-wave action are studied. Results of x-ray phase analysis suggest stabilization of the new high-pressure phase δ'-Al₂O₃ with a face-centered cubic lattice with a parameter a = 8.53 Å.
Key words: metastability, corundum, shock-wave synthesis, surface, modification.

The paper reports results of metallographic studies of specimens of St. 3 steel and M1 copper loaded by shock waves of various intensity (p≈2