Home – Home – Jornals – Combustion, Explosion and Shock Waves 2016 number 5

Combustion of solid propellant charges in rocket propulsion systems usually occurs under conditions of intense flow of combustion products (solid rocket motor), gaseous oxidizer (hybrid rocket motor) or air (ramjets and air-breathers).This causes the so-called erosive burning effects, resulting in a change in the burning law under the influence of the gas flow. The main approaches to modeling the erosive burning of solid fuels in high-velocity gas flow are considered. Methods for the criterial description of the results of experimental studies of the erosive burning of solid fuels under transonic and supersonic flow conditions are analyzed.

Stability of diffusion combustion of fuel jets impacting on targets and interaction of two jets (pure propane-butane and the same fuel with addition of carbon dioxide) are experimentally studied. Data on combustion failure are obtained for various variants of jet interaction, as well as information about the composition of combustion products, air-to-fuel ratio, and completeness of combustion before combustion failure. It is shown that the domain of stable combustion of impacting and opposing jets is expanded by more than an order of magnitude as compared to combustion of individual free jets.

This paper presents the results of two large-scale tests performed to clarify the conditions for the detonation of propane-air compositions in model surface clouds in the absence and in the presence of confining rigid walls. Model clouds with sizes of 15 x 6 x 4.2 and 15 x 6 x 2 m were confined by plastic tents. A mixture of starting reactants in the cloud was ignited by the hot detonation products propagating along a perforated 0.82 x 23 m tube passing through the space of the tent. Hot detonation products were injected from the tube through holes of 20 and 40 mm diameters. Detonation of the propane-air mixture in the tube was initiated by explosion of an explosive charge placed at the tube end. Detonation occurred in the propane-air cloud bounded on one side by a rigid vertical wall, and no detonation was observed in the cloud with similar injection of hot products without a rigid wall. It is concluded that the divergence or convergence of the flows of hot detonation products play a key role in the process, being responsible for the presence or absence of detonation in the mixing region, respectively.

The activity of plates of CuO/Al2O3/FeAlO/FeAl ceramic metal structured catalysts is compared by varying the alumina content in them. The catalysts were prepared by impregnation of the ceramic metal carriers obtained by mechanochemical activation of powder mixtures of an alumina precursor (20-50% (wt.)), iron and aluminum, followed by hydrothermal treatment and calcination. It is shown that with increasing content of the alumina precursor (product of thermal activation of hydrargillite) increases the specific surface area of the carrier and meso- and macropore volume and reduces its mechanical strength. The content of the active component (CuO) also increases, resulting in an increase in the specific activity of the catalyst despite a reduction in the effectiveness of using the active component. The activity of catalysts with a medium concentration of alumina is sufficient to initiate oxidation of methane.

On the basis of physical concepts and the results of thermal theory of combustion, the qualitative analysis and mathematical simulation of transformation of steady temperature distributions along the length of the adiabatic reactor. It is revealed that, with a certain amplitude and a frequency of harmonic perturbations of the velocity of reagents, it is possible to increase the thermal stability of the process (obtain the pre-explosion heating).

Results of an experimental study of ignition of a water-coal fuel in a high-temperature air flow are presented. The fuel is obtained on the basis of the mark D coal or filtrational cake of the Severnaya dressing plant. Based on the experimental results, physical and mathematical models of the processes of thermal preparation and ignition of water-coal fuel particles are formulated, which take into account the joint proceeding of the most relevant physical and chemical transformations (which exert an essential effect on the ignition condition) and the processes of heat and mass transfer during the induction period. A comparison of the basic ignition characteristics (ignition delay time and limiting values of the gas medium temperature), which are obtained experimentally and theoretically (based on results of numerical simulations), leads to a conclusion that the water film affects the dynamics of the ignition process.

The first mode is implemented partial oxidation carbonized residue in coal vodokislorodnogo fluid stream at a temperature of 923 K and a pressure ~30 MPa. Detected flow coupled processes of oxidation and carbon balance formation of inflammable gases (hydrogen content in the products increase by 26 % its relative amount in the original sample) due to the participation of the molecules H2O in redox reactions.

Despite significant progress in studying thermal decomposition of ammonium dinitramide (ADN), the kinetics of the process at the level of elementary stages has not been adequately studied. The aim of this review is to summarize various published data, which are of interest for studying and simulating the processes of thermal decomposition and combustion of ADN. Considerable attention is paid to physical and chemical properties of ADN, dinitramide and its anion N(NO2)2-, which play a key role in ADN decomposition. Various channels of decomposition of ADN, dinitramide, and N(NO2)2- are discussed. Results illustrating alternative points of view on the decomposition process are presented.

The problem of mixing of the products of detonation of composite explosives is of principal importance for the synthesis of ultrafine diamond from composite mixtures and also for chemistry of detonation processes as a whole. An analysis of mixing in the chemical reaction region due to molecular diffusion shows that this mechanism may be important only for grain sizes of several micrometers. If the grain sizes reach tens or hundreds of micrometers, only partial mixing on the grain boundaries is possible. Investigations of the hydrodynamic mechanism of mixing shows that it may occur owing to a nonuniform velocity field behind the detonation wave front in the mixture and to the development of turbulence and cumulative processes during pore implosion. In mixtures with grain sizes of the order of 30 m, these processes can lead to appreciable mixing during the time of »0.5\s and longer. Theoretical estimates are compared with the results of experiments performed at the Lavrentyev Institute of Hydrodynamics of the Siberian Branch of the Russian Academy of Sciences and at the Altai scientific and industrial enterprise (Biisk) for studying the synthesis of ultrafine diamond with the use of the isotope technique.

This paper describes the results of experiments on laser initiation of composites based on PETN and inclusions of submicron coal particles. The thresholds and kinetic characteristics of explosion of mixed compositions based on PETN and inclusions of submicron coal particles (B and DG) are studied under the influence of neodymium laser (1064nm, 12 ns), depending on the mass concentration of inclusions in the range of 0-5%. It is shown that the minimum threshold of explosive decomposition of PETN equal to 1.1 J/cm2 can be achieved if the concentration of both types of inclusions is 0.5%.

The formation of shaped-charge jets from hemispherical copper liners of degressive (decreasing from top to bottom) thickness is analyzed by numerical simulation of a two-dimensional axisymmetric problem of continuum mechanics. The basis for the comparison was taken to be the parameters of the jet formed from a modern standard shaped charge with a conical liner which provides penetration of a steel target to a depth equal to 10 charge diameters. In the comparative analysis, we used calculated mass-velocity distributions and the ultimate jet length-velocity distributions obtained on the their basis, from which the potential penetrability of jets was evaluated. It is shown that the use of hemispherical cumulative liners of degressive thickness makes it possible to form shaped-charge jets that are not inferior in head velocity and penetrability to the jets from conical liners.

Investigations of specific features of the microstructure of the region where a spall crack transforms to an adiabatic shear band are based on a spall model of strain localization, which implies that adiabatic shear bands are induced by interference of unloading waves, and the value of the negative stress in the expansion region of these waves does not exceed the dynamic strength of the material. It is shown that the transition region contains a tremendous number of dislocation ensembles, which is much greater than the number of dislocation ensembles generated by a shock wave. Detection of micrometer-sized fracture sites in the region of interference of unloading waves implies that small fracture sites are formed in a polycrystalline material on dislocations arising in the course of dynamic tension.