Home – Home – Jornals – Combustion, Explosion and Shock Waves 2013 number 1

The heating of the wall of a reactor at the third ignition limit was measured during induction and explosion. It is shown that the heat released during induction is approximately equal to the heat released during explosion. It is established that in the induction period and below the limit, the reaction rate changes by a factor of about 10 with a change in the order of consecutive supply of hydrogen and oxygen to the reactor. This means that in these cases, the reaction occurs mainly on the wall of the reactor. The total amount of hydrogen peroxide and the peroxide radical HO₂ below the third ignition limit was measured. It is shown that these intermediate products are formed in an autocatalytic heterogeneous reaction. It is established from the sum of the data from the experiments and the literature that an detonating gas explosion at the third limit is degenerate. The explosion is the result of accumulation and decay of the intermediate product in the gas, which is hydrogen peroxide produced mainly in the wall of the reactor.

The structures of three laminar premixed stoichiometric flames at low pressure (6.7 kPa): a pure methane flame, a pure ethanol flame, and a methane flame doped by 30% of ethanol, have been investigated and compared. The results consist of mole fraction profiles of CH₄, C₂H₅OH, O₂, Ar, CO, CO₂, H₂O, H₂, C₂H₆, C₂H₄, C₂H₂, C₃H₈, C₃H₆, CH₃–C≡CH (propyne), CH₂=C=CH₂ (allene), CH₂O, and CH₃HCO, measured as a function of the height above the burner by probe sampling followed by on-line gas chromatography analyses. Flame temperature profiles have been also obtained by using a PtRh thermocouple. The similarities and differences between the three flames have been analyzed. The results show that, in these three flames, the mole fraction of the intermediates with two carbon atoms is much larger than that of the species with three carbon atoms. In general, the mole fraction of all intermediate species in the pure ethanol flame is the largest, followed by the doped flame, and finally the pure methane flame.

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.

Results of studying the effect of K₂CO₃ additives on the grain size of the products of combustion of a gas suspension of Al particles (with the mean particle diameter of 4.8 mm) in a laminar diffusion flame are reported. An extreme character of the dependence of the mean size of Al₂O₃ particles on the additive concentration is experimentally observed. For the concentration of the K₂CO₃ additive equal to 0.5%, the mean diameter of Al₂O₃ particles is 30 nm; for the additive concentration of 5%, the mean particle size increases to 67 nm. It is demonstrated that the change in the mean size of A₂O₃ particles as a function of the concentration of the readily ionized additive is caused by interaction of the dusty and ionic subsystems of the plasma of the combustion products in the reaction zone in the flame. At a high concentration of ions (above 10²⁰ m^-3), this interaction increases the rate of coagulation of Al₂O₃ particles.

A model is proposed for the steady-state combustion of a mixture of a pyrolyzed solid fuel and an inert material in a countercurrent gaseous oxidizer. The chemical scheme includes the pyrolysis of the original fuel with the formation of a coke residue and gaseous products (pyrolysis tar), oxidation of pyrolysis tar, and oxidation of the coke residue. The process in an infinite nonadiabatic reactor is considered. The one-dimensional single-temperature model includes the energy conservation equation for the system and the mass conservation equations for each species. The original system of equations is solved for each type of thermal structure of the combustion wave (normal and inverse) using an asymptotic method and assuming a narrow combustion zone. Analytical relations between the main macrokinetic parameters of the process are obtained. It is shown that at la ow content of the inert components (in the parametric domain of inverse waves), pyrolysis completely proceeds in a zone distant from the combustion front. In the region of normal waves, more complete combustion of the fuel is observed, which is provided by oxidation of part of pyrolysis tar.

Modeling of the combustion of cyclic nitramines (CNAs) has shown that their combustion proceeds by the same mechanism with the joint effect of the processes in the condensed and gas phases. The combustion characteristics of the pure substances can be changed only at low pressures by using catalysts acting in the condensed phase, and at high pressures, this problem is difficult to solve. The combustion of binary compositions [CAN + fuel (F), CAN + ammonium perchlorate (AP)] and ternary compositions (AP + CAN + F) is considered. It is shown that the combustion mechanism and characteristics are determined by the chemical interaction and heat exchange between the reactants, which depend on the characteristic particle size in the system.

A pointwise semi-empirical mathematical model is proposed, which ensures a reasonably accurate description of experimental data on the ignition delay of iron particles as a function of ambient temperature with allowance for the dependence of the limiting ignition temperature on pressure.

A two-dimensional unsteady gas-dynamic mathematical model of continuous spin detonation in a non-stoichiometric hydrogen–oxygen mixture in an annular combustor of a rocket-type engine is formulated. An analysis of the governing parameters shows that this model is an eigenvalue problem, where the eigenvalue is the problem period, which cannot be arbitrarily prescribed, but which has to be sought in the course of solving the problem. Numerical modeling of the dynamics of transverse detonation waves is used to elucidate the influence of the fuel-to-oxidizer equivalence ratio on the wave structure and specific impulse, and the eigenvalue (minimum period of the problem) is determined as a function of the specific flow rate of the mixture. These eigenvalues are demonstrated to agree with experimental data. In the case of continuous spin detonation, addition of an expanding nozzle to a constant-section channel is shown to increase the specific impulse.

Loose packed PETN initiation by a hot gas flow generated by an explosion of an active charge separated by an air gap is studied. Experimental data obtained by means of synchrotron radiography are compared with simulations employing a two-phase two-velocity two-temperature model. Reasonable agreement is reached by taking into account two processes accelerating the reaction: particle fragmentation during powder compaction and combustion intensification due to instability of the evaporating surface layer excited by a high-velocity gas flow around the particles.

A model of a wide-range semi-empirical equation of state for metals is presented. The specific heat and Grüneisen coefficients of ions and electrons are functions of temperature and density. At low temperatures, the heat capacity varies according to Debye theory. The removal of the degeneration of the electron gas with increasing temperature is taken into account. The effect of ionization on the thermodynamic functions is effectively taken into account. The equation of state allows the calculation of states in a two-phase liquid–vapor region. This model was used to develop the equations of state for Ta, W, Al, and Be. For its range of applicability, the equation of state contains a relatively small number of free parameters, most of which have a physical meaning. Comparison of calculations of various isolines using equations of state with experimental data and calculations based on other models show that the equations of state for Ta, W, Al, and Be, describe most experimental data for these substances. At ultrahigh pressures and temperatures, calculations using the equations of state are in good agreement with calculations using the Thomas–Fermi model with corrections.

The relation between the parameters of mixed explosives [combinations of Al(NO₃)₃ × 9H₂O powder, RDX powder, and/or polyethylene foaming particles] and the phase and dimension of ultrafine Al₂O₃ is studied in this paper. Experimental results indicate that mixed explosives with a high density of 1.8 g/cm³ are adapted to prepare high-temperature α-A₂O₃. Ultrafine (α + γ)-Al₂O₃ with α-phase dominance is synthesized by the detonation of charges with a medium-high density of 1.3 g/cm³. Explosives with a medium-low density of 0.8 g/cm³ synthesize low-temperature pure γ-Al₂O₃.

This paper presents experimental data on the penetration of shaped charges with porous liners into metal targets located at distances smaller than or comparable to the diameter of the charge and some experimental data on the velocity of the jets from the investigated charges with liners of metal powders.

Combustion of furazanotetrazine dioxide (FTDO) was studied in a constant-pressure bomb in the range of pressures 0.1 ÷ 10 MPa. The thermal decomposition kinetics of FTDO in melt under non-isothermal conditions at temperatures 153 ÷ 179 °C was measured. The rate constants of the non-isothermal decomposition are described by an equation with an activation energy of 26.5 kcal/mol. It is concluded from the studies performed that the combustion of FTDO in the entire investigated pressure range obeys the gas-phase model, i.e., the leading combustion reaction is located in the flame.

The brightness temperature of shock-compressed EC141 NF epoxy resin was measured by a pyrometric method in the pressure range of 19 ÷ 42 GPa. The experimental points are in good agreement within the error with the calculation performed in the work. From the results of experiments, it follows that the presumed phase-transition region is not apparent in the pressure –temperature plane. Particle velocity records at the epoxy–water interface suggest the absence of a chemical reaction in EC141 NF epoxy compound at a pressure of 22.5 GPa during the observation time.