A. D. Rychkov

Ignition and extinction of homogeneous energetic materials by a light pulse

Numerical calculations using a model of unsteady combustion of melting energetic materials were performed to simulate the results of qualitative experiments on the ignition and quenching of energetic materials by a light pulse. The parameters of the model composition were chosen to correspond to combustion with the burning-rate control reaction in the gas phase to ensure the stability of self-sustained combustion after the cessation of irradiation. Regions of stable ignition in the coordinates “radiant flux amplitude-irradiation time” were obtained for compositions with different transparency for igniting pulses of three shapes: rectangular, linearly decreasing to zero, and exponentially decreasing. Extinction conditions of the steadily burning composition by a rectangular light pulse were calculated.

Macrokinetics of Combustion of Monodisperse Agglomerates in the Flame of a Model Solid Propellant

The paper describes a procedure for studying the macrokinetics of combustion of agglomerates in a solid propellant flame using special samples of a model propellant generating monodisperse agglomerates. Empirical dependences of the incompleteness of aluminum combustion in the combustion products of a propellant based on ammonium perchlorate and HMX on time and pressure were established. The mass fraction of oxide accumulated on a burning agglomerate versus the degree of aluminum conversion was determined. For fine agglomerates (310–350 μm), this fraction decreases with increase in the degree of conversion. For large agglomerates (400–540 μmum), it increases, and, hence, the mass of large agglomerates increases as aluminum burns out. Because of accumulation of oxide, the agglomerate size does not change markedly in the examined range of parameters.

INSTABILITY OF A COMBUSTION MODEL WITH SURFACE VAPORIZATION AND OVERHEAT IN THE CONDENSED PHASE

Using numerical modeling, we have revealed the instability of a steady-state combustion regime which was previously obtained using analytical methods in the substance-combustion model with surface vaporization and with exothermic reactions in the condensed phase which are intense enough to form a maximum of temperature underneath the surface. The instability has been studied analytically using the method of small perturbations to eliminate the version of its nonphysical (numerical) character. Steady-state combustion regimes with maxima on the condensed-phase temperature profile are shown to be actually unsteady. It is suggested that convection in a liquid-subsurface layer owing to bubble motion caused by the Marangoni effect should be taken into account to describe correctly the experimentally observed steady-state regimes with a leading role of the condensed phase.

Calculation of the response of a gasifying energetic material exposed to monochromatic radiation

It is shown that the steady-state gasification of a homogeneous energetic material with exothermic subsurface reactions has stability boundaries for small and large values of the radiant flux. Examples of corresponding calculation using a transient combustion model are given. A possible method of accounting for the subsurface reactions on the transparency of an energetic material is considered (with examples of numerical calculation). The gasification rate response function of an inert material to small variations in the radiant flux is found analytically. Knowledge of this function allows one to obtain information on some thermal and optical characteristics of an energetic material using relatively simple experiments.

Ignition of Filtration Gas Combustion Waves by the Flame of the Filtered Gas

Mathematical modeling of ignition of filtration gas combustion waves in a porous medium with external initiation of combustion by the filtered gas is performed. It is shown that the surface temperature of the porous medium at which the flame enters the latter is a function of system parameters. The existence of the lower and upper flammability limits in terms of the gas filtration rate is found. Dependences of the ignition time on parameters of the porous medium are obtained, and their interpretation is given.

Modeling of operation of a solid-propellant pulse aerosol generator during extinguishing of methane-air mixture ignition in coal mine drifts

Operation of a pulse aerosol system of extinguishing fires caused by ignition of a methane-air mixture in drifts and coalfaces of coal mines is modeled. A computational experiment shows that such a system can cut off the shock wave propagating over the coal mine drift filled by a combustible methane-air mixture, suppress burning, and protect people and equipment in the mine from the shock wave action.

Filtration Combustion of an Energetic Material in a Cocurrent Flow of Its Combustion Products. Critical Combustion Conditions

The paper reports results of a numerical calculation using the three‐temperature model developed previously by the authors. In addition to the temperature difference between the gas and the solid phase (skeleton), the model approximately takes into account the temperature distribution in skeleton elements. It is shown that quenching is possible (after burnout of part of the charge) with variation in a number of input parameters: the thermal conductivity of the charge, the ignition temperature, the weight of the igniter, the initial temperature, the porosity of the charge, and the local rate of its decomposition.

Simulation of the dispersion and ignition of fine-dispersed aluminum particles by a gas generator

Using numerical modelling, we studied the formation and propagation of a cloud of fine-dispersed aluminum particles generated by a special unit under the action of high-temperature combustion products of a solid propellant gas generator, as well as the ignition conditions of these particles. The results of numerical modelling show that the dynamic characteristics of the cloud of particles and their ignition substantially depend on the temperature of gas generator combustion products, particle sizes, and the energy characteristics of the generator itself. The results obtained are in a qualitative agreement with experiments carried out at the Fraunhofer Institute for Chemical Technology (Pfinztal, Germany) [6].

Mathematical models of filtration combustion and their applications

The short review of the works in the field of mathematical modelling of filtration combustion, which are carried out in the research centers of Russia, is presented. The main attention is given to computational aspects. The examples of the numerical solution of three typical problems: filtration combustion of gas mixture in inert porous medium, combustion of fuel granules in hard fuel gas generator, and non-stationary combustion of hard fuel in automotive safety device (airbag) are presented.

Two-stage ignition of energetic materials with a liquid surface layer

Two-stage ignition regimes of energetic materials with a liquid surface layer were revealed by mathematical modeling of transient combustion processes. First, under the action of a radiant flux, the regime of forced gasification of a condensed phase with a degree of its surface depletion of 0.1–0.3 was observed. Gas-phase combustion occurs in the blow-off regime. As the radiant flux decreases, the gas flame approaches the surface and becomes determining, and the degree of condensed-phase depletion decreases.