Home – Home – Jornals – Combustion, Explosion and Shock Waves 2014 number 5

The modes of operation of a flow reactor with an inert inner body were investigated. A numerical study of the combustion of a methane-air mixture was performed. The parameter ranges of possible modes of reactor operation were determined depending on the dimensionless parameters of heat exchange of the mixture with the inert body and the side surface and the mixture flow parameter. The existence of non-uniqueness regions of operation modes is shown. The influence of the inert inner body on the distribution of the regions of possible modes of reactor operation is considered.

Limitations of the spatial and temporal resolution of the particle image velocimetry (PIV) technique in velocity field measurements in a laminar flame have been investigated. The limitations are due to the need to introduce a suspension of tracer particles into the flow. For a methane-air mixture with a stoichiometry coefficient of 0.9, it is determined that at a mass fraction of TiO₂ solid particles over 0.08%, the change in the flame propagation velocity by the particles exceeds 5%. The maximum spatial resolution of PIV for which the influence of the particles is insignificant corresponds to a concentration of 0.03%; in this case, the minimum resolvable scale is limited by a value 200 times larger than the size of tracer particles. Based on analytical estimates and a comparison of measured and numerically calculated particle velocities in the flame, it is concluded that particles smaller than 2 mm adequately track the flow velocity. Under these conditions, the error of the velocity measurement is mainly determined by the limited spatial resolution of PIV. The results of the work can be used to evaluate PIV measurement errors in other experimental studies of flames.

The dependences of the characteristics of filtration combustion of a mixture of carbon particles (10%) and an inert material on the oxygen content (5-50%) in a filtered gas are experimentally studied. The oxygen concentration in the injected gas is varied at a constant total gas flow rate in the first series of experiments and at a constant oxygen flow rate in the second series. It was found that, in both cases, the combustion wave structure changes along with the oxygen concentration. The temperature increases monotonically with the oxygen concentration at a constant total gas flow rate and passes through a maximum value at a constant oxygen flow rate. The maximum yield of carbon monoxide in both series of experiments is reached in the region of thermal wave structure inversion.

This paper presents the results of theoretical and experimental studies of the combustion of rapeseed methyl ester droplets in comparison with mineral diesel fuel. Droplets of 0.7-1.2 mm diameter were investigated. The effect of the oxidizer equivalence ratio in the range of 1.7-4.0 on the duration of droplet combustion was analyzed using the model of combustion of droplets in an adiabatic shell taking into account Stefan flow. It is shown that the burning time of rapeseed methyl ester droplets is smaller than that of diesel fuel droplets, all other things being equal.

The processes of combustion and phase separation in thermite SHS systems in the synthesis of cast composite materials based on the silicides of molybdenum, tungsten, niobium, and titanium in a wide range of ratios between them have been studied. Thermodynamic calculations for the hot MoO₃/2Al/2Si and WO₃/2Al/2Si systems have shown that the pressure has a the strong effect on the combustion temperature and yield of gaseous products, and for the cold 3Nb₂O₅/10Al/12Si and 3TiO₂/4Al/6Si systems, this effect has not been found. The effect of the ratio of the initial reagents and the activating high-temperature additive (CaO₂ + Al) on the combustion and phase-separation parameters have been studied experimentally.

The possibility of obtaining refractory titanium nitride TiN in a calciothermic process is shown. The dependence of the combustion rate and temperature on the nitrogen pressure is studied. The phenomenon of super-adiabatic heating during combustion of the Ca - TiO₂ - N₂ system is found.

The effect of the phase composition of an aluminum-based alloy powder containing 1.3% calcium and the products of its interaction with air on the kinetics and mechanism of oxidation was first shown by x-ray diffraction using synchrotron radiation. It was found that the high surface and chemical activity of calcium led to an increase of more than a factor of two in the completeness of the process in the temperature range of 1300-1550 K upon heating at 10 K/min.

This paper presents an analysis of the possibility of improving the ballistic performance of solid rocket propellants by using the a-modification of hexanitrohexaazaisowurtzitane (CL-20) as a component of solid crystal hydrates or crystal solvates. If small molecules (water, hydrazine, and methanol) occluded in the main material are enclosed in the structural cavity of the crystal of the main component and, consequently, the crystal lattice parameters do not change relative to the original compound, then, there is a real opportunity to improve the ballistic performance of the rocket propellants developed on the basis of the original energetic compound by increasing the density of the component.

Based on the developed physicomathematical model of detonation attenuation and suppression in a methane-oxygen mixture by means of addition of a cloud of inert particles, the influence of the volume fraction of particles and their diameter on the detonation wave velocity is analyzed. Detonation limits in terms of the volume fraction of particles in methane-oxygen and methane-hydrogen-oxygen mixtures are found. A comparison with our previous data on suppression of detonation in a hydrogen-oxygen mixture shows that the critical volume fractions of particles resulting in detonation wave suppression in the methane-hydrogen-oxygen mixture are greater than those in the hydrogen oxygen mixture.

Shock-wave and detonation flows in a two-phase medium consisting of a gas and incompressible particles are studied by methods of numerical simulation with allowance for the random motion and collisions of particles. Steady solutions corresponding to two previously predicted wave types are obtained for the problem of interaction of a plane shock wave with a cloud of particles. The influence of the mixture parameters on the corresponding solutions is determined. In considering the problem of propagation of cellular heterogeneous detonation in a mixture of reacting particles, oxidizer, and inert particles, it is found that the detonation flow structure and the cell size are retained in the mixture with particle collisions. However, smearing (dispersion) of the layers and inert phase structures formed in the far zone of cellular detonation occurs because of particle collisions.

The problem of continuous spin detonation in a supersonic flow in a flow-type annular combustor is considered in a two-dimensional unsteady formulation. The dynamics of the detonation wave in a hydrogen-oxygen mixture with isentropic and shock-wave compression of the flow in the input diffuser is studied. It is shown that the mass flow rate of the mixture through the combustor decreases as continuous spin detonation is formed, and a steady regime with a “detached” shock wave is observed at the entrance of the supersonic diffuser. For a contoured combustor, the limit from above is obtained for the Mach number of the incoming supersonic flow at which a continuous detonation regime is obtained.

The conventional Zel'dovich-von Neumann-Döring (ZND) detonation theory is modified with two-dimensional velocity vectors to account for the performance and steady-state flow features of a rotating detonation engine. The developed analytical model explains many of the steady-state features of the rotating detonation and its thermodynamics. The generation of swirl is shown to be the primary mechanism of energy transfer.

Pulsed laser initiation is used to experimentally investigate the thresholds of explosive decomposition of PETN-based compounds with aluminum nanoparticle inclusions depending on the core-shell (Al/Al₂O₃) mass ratio in the particle. It is found that, with decreasing mass fraction of Al from 74 to 13%, the explosive decomposition threshold increases by a factor of 12.5. Light absorption efficiency calculations for the core-shell system performed by the Aden-Kerker method for Al/Al₂O₃ inclusions in PETN show that this efficiency decreases with decreasing mass of metal in the particle. The experimental and theoretical results can be regarded as an additional confirmation of the hot-spot concept of laser initiation of PETN containing nanoscale inclusions of metals.

A semi-empirical equation of state for iron with allowance for five condensed phases (α, γ, δ, ε, and liquid phases), evaporation, and thermal ionization is derived. As a whole, results of model calculations are consistent with static and dynamic experimental data in the pressure range from the atmospheric value to ≈10 TPa and in the temperature range from room temperature to ≈10⁵ K. The viscosity of liquid iron under conditions typical for the Earth core is estimated on the basis of the liquid model.

A semi-empirical wide-range equation of state of compounds of lithium isotopes with hydrogen isotopes is proposed. This equation allows thermodynamic properties to be calculated both in the range of comparatively small densities, pressures, and energies available for experimental studies and in the range of superhigh densities, pressures, and energies where the states can only be estimated at the moment by calculations in accordance with theoretical models. The equation of state contains empirical functions, which allow the composition of the isotopes and the influence of the hydroxide admixture on the compound properties to be taken into account. The capabilities of the equation of state are demonstrated by an example of the description of experimental and numerical data characterizing thermodynamic and thermophysical properties of several compounds of lithium and hydrogen isotopes.

The dependences of the detonation velocity and the propellant performance measured using the M-40 technique on the charge density for aluminized explosives with different mass fraction of Al were studied. The fractions of the energy of Al combustion utilized during the chemical reactions and during the acceleration of the flyer plate were estimated. Regression dependences of the detonation velocity and the propellant performance on the charge density were obtained. The effect of the addition of particulate Al, Ti, Zr, and W in an amount of 5-30% on the detonation velocity of high-density explosive charges based on plasticized RDX was investigated. It is found that the reduction in the detonation velocity with the addition of various metallic additives is determined by the longitudinal sound velocity of the additive, and not by its density. Simple formulas for calculating the detonation parameters of high-density metallized explosives were obtained.

A new laboratory express-method of determining the specific impulse of solid propellants based on the measurement of the reactive force of gasification products escaping from the burning propellant surface is presented in this work. The values of the specific impulse for a model composite solid propellant by varying the pressure in the combustion chamber are determined.