Vol 52, No 5 (2016)

Combustion of solid propellants in rocket propulsion systems usually occurs in an intense cross-flow of combustion products (solid rocket motor), gaseous oxidizer (hybrid rocket motor) or air (ramjet and air-breathing engines). This leads to 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 propellants in a high-velocity cross-flow of gases are considered. Methods for the criterial description of the results of experimental studies of the erosive burning of solid propellants under transonic and supersonic flow conditions are analyzed.

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 dimensions of 15 × 6 × 4.2 and 15 × 6 × 2 m were confined by plastic tents. A mixture of the starting reagents in the cloud was ignited by hot detonation products propagating along a perforated ø0.82 × 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 plays a key role in the process, being responsible for the presence or absence of detonation, respectively, in the mixing region.

The physical concepts and the results of the thermal theory of combustion are used as a basis for the qualitative analysis and mathematical simulation of transformation of stationary temperature distributions along the length of an adiabatic reactor in the case of periodic perturbations of the velocity of the reagent in the reactor and its temperature at the entrance of the reactor. It is established that, with certain values of the amplitude and frequency of harmonic perturbations of the velocity of the reagent, it is possible to improve the thermal stability of the process (increase the pre-explosion heating).

The autothermal regime of partial oxidation of carbonized coal residue in a stream of water-oxygen fluid at 923 K and 30 MPa is implemented for the first time. It is revealed that the oxidation of coal residue and the formation of combustible gases (hydrogen content in the products is increased by 26% with respect to its amount in the original sample) occur simultaneously and are caused by the participation of the H₂O molecules in the redox reactions.

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 μm, these processes can lead to appreciable mixing during the time of ≈0.5 μs 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 method.

The formation of shaped-charge jets from hemispherical copper liners of degressive thickness (decreasing from apex to bottom) is analyzed by numerical simulation of a twodimensional axisymmetric problem of continuum mechanics. The comparison was based on 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. The comparative analysis was performed using calculated mass–velocity distributions and the ultimate jet length–velocity distributions obtained on their basis, from which the potential penetrability of jets was evaluated. It is shown that the shaped-charge jets formed by hemispherical shaped-charge liners of degressive thickness are comparable in head velocity and penetrability to the jets from conical liners.