Energy Release Zone Research Articles

Evaluation of Prediction Ability of Detailed Reaction Mechanisms in the Combustion Performance in Hydrogen/Air Supersonic Flows

Comparative analysis of the prediction ability of several modern detailed kinetic models describing the ignition and combustion of hydrogen/air mixture in a supersonic flow is conducted. The possible uncertainties in the rate constants of principle reactions responsible for the chain mechanism development in the H2/O2(air) mixture are inspected. Special attention is paid to matching the lengths of ignition and energy release zones and combustion completeness predicted by considered kinetic models in both one-dimensional homogeneous premixed flow and two-dimensional non-premixed flow in a scramjet model combustor. It is demonstrated that, while the difference in the induction zone length predicted by considered kinetic models does not exceed 30%, the discrepancy in the calculated values of energy release zone length may be as large as a factor of 4. As a consequence, different reaction mechanisms give distinguished magnitudes of combustion completeness at the combustor exit.

Highly magnetized region in pulsar wind nebulae and origin of the Crab gamma-ray flares

The recently discovered gamma-ray flares from the Crab nebula are generally attributed to the magnetic energy release in a highly magnetized region within the nebula. I argue that such a region naturally arises in the polar region of the inner nebula. In pulsar winds, efficient dissipation of the Poynting flux into the plasma energy occur only in the equatorial belt where the energy is predominantly transferred by alternating fields. At high latitudes, the pulsar wind remains highly magnetized therefore the termination shock in the polar region is weak and the postshock flow remains relativistic. I study the structure of this flow and show that the flow at first expands and decelerates and then it converges and accelerates. In the converging part of the flow, the kink instability triggers the magnetic dissipation. The energy release zone occurs at the base of the observed jet. A specific turbulence of relativistically shrinking magnetic loops efficiently accelerates particles so that the synchrotron emission in the hundreds MeV band, both persistent and flaring, comes from this site.

Excitation of a system of electromagnetic oscillators in the field of a remote microwave radiation source. Part 1. High-Q systems

Results of simulation and experimental testing of a method of forming a periodic temperature profile on the surface of a dielectric body are presented. The temperature profile is formed by a system of passive electromagnetic (EM) oscillators heated in the field of a quasi-optical beam of external microwave radiation. It is shown that, in a system of parallel linear high-Q oscillators of a resonance length, a multimode EM-field structure is formed, which hampers formation of a uniform periodic structure of energy release zones and, therefore, formation of a regular temperature profile on the model’s surface. Feasible ways of solving this problem are proposed, including application of linear EM oscillators situated near a conducting reflecting screen at a distance much shorter than a quarter wavelength of the radiation.

Modeling of explosion thermal radiation

The hydrodynamic and radiation processes accompanying explosions of chemical explosives and fuel-air mixtures have been considered. Computer modeling of the radiation from a fire ball of explosion and a flame of diffusion combustion of a hydrocarbon fuel has been performed. The dependences of the heat flux density from the region occupied by explosion and combustion products on its temperature and geometric characteristics have been determined. Thermal load distributions on targets of different orientations in the vicinity of the energy release zone have been obtained. A comparison of the thermal parameters on radiation detectors with the criteria of thermal affection of people and ignition of combustible materials has been made.

Optimization of supersonic flows past thin bodies by using external effects on the flow

Problems of optimization of flows past a thin body of revolution and a slender profile at a small angle of attack in the presence of local energy release zones and an external force acting on the flow near the surface are considered. Analysis is based on an analytic theory of supersonic flow past thin bodies presented in previous papers. The following problems are considered: drag reduction of a thin body of revolution, lift force enhancement of a profile with infinite aspect ratio, attenuation of acoustic noise generated by supersonic flows past bodies.

Supersonic flows with small perturbations in the presence of external effects on the flow. II. Slender wing profile

An analytic theory of a supersonic flow past a slender profile of an arbitrary shape in the presence of local energy release zones and an external force acting on the flow near the surface is developed. Main results are obtained using the linear approximation, which is valid in a wide range of external conditions. Analytic expressions are derived for calculating the spatial distributions of pressure perturbations near the surfaces of a slender profile at a small angle of attack. The results of analytic calculations are compared with the numerical simulation data based on the Euler equations for a wedge at a zero angle of attack. The comparison reveals good agreement between numerical and analytic calculations. The results make it possible to formulate and solve optimization problems for a supersonic aerodynamic flow with the help of external effects on the supersonic flow.

Evolution of the glow of an aerogel irradiated with a high-power pulse electron beam

The evolution of the glow of the energy-release zone in porous transparent aerogel, with a density of 0.03–0.25 g/cm3, which is irradiated by a high-power pulse electron beam, is studied experimentally. In addition to a fast (τ≤τbeam) and a luminescent (τ≈10−6 s) glow components, a slow glow component (τ≈2×10−5 s) has been revealed. The appearance of this slow component is associated with an aerogel rarefaction wave and its destruction (cracking) arising after its isochoric bulk heating by electron radiation, which may occur due to an electrostatic field induced under irradiation. The discovered glow is utilized to visually determine the current position of the rarefaction wave front. The sound velocity measured as a function of the density of SiO2 aerogels with porosities of 10–100 allowed us to experimentally determine the percolation parameter of the aerogel equation of state.

Determination of the dynamic characteristics of aerogels in the energy-release zone of a high-power electron beam

The dynamics of the interaction of a high-current electron beam with SiO2 aerogels of different density and porosity are investigated by optical methods. A model for describing highly porous materials is developed on the basis of the information obtained regarding the unloading of aerogels in the energy-release zone of an electron beam, as well as the measured energy-release profiles. A corresponding nonlinear self-consistent equation of state is obtained which reflects the fractal properties of aerogels and permits determination of the thermodynamic characteristics of aerogels as the porosity varies tens of times. The influence of electric space charge on the energy-absorption profile of a high-power electron beam in aerogels of different density is discussed.

Gas dynamics with local energy release in subsonic and supersonic flow

The flows developing in the interaction of a supersonic gas stream with a continuously operating axisymmetric energy release source or as a result of the action of pulsed periodic energy injection on a subsonic gas stream are investigated numerically. For a continuously operating energy source two types of flow can be distinguished: with a shock wave detached from the source and with a shock attached to it. Approximate formulas for the gas density in the center of the energy release zone are obtained for the cases of constantly operating and periodic energy sources.

Effect of energy release in shock layer on supersonic flight

The presence of an energy release zone in a supersonic stream leads to the formation of perturbations propagated from the source of energy release [1, 2]. The action of such a stream on a body past which it flows is determined by the strength of the source and the configuration and location of the energy release zone. The dependence of the aerodynamic characteristics of a blunt cone on the parameters of the source of energy release is analyzed on the basis of the results of a numerical integration of the equations of motion of the gas.

Calculations of gas flow in the energy-release zone in a cylindrical explosion

A numerical investigation of the problem of a cylindrical symmetrical explosion in a stationary gas is presented. Various types of energy-releasing distribution function with respect to the radius are considered. Using the theory of dimensions the laws of similitude characterising the rate of development of gas-dynamic processes in the region of action of the source are obtained. The influence of the form of energy source on the power of the wave produced by the explosion is investigated.

A scaling model for plasma columns produced by CO2 laser-induced breakdown in a solenoidal field

An analytical model is derived for the plasma cylinder produced by a long pulse (approximately μsec) CO2 laser of power pl (watts) which is incident upon neutral hydrogen imbedded in a strong axial magnetic field. Under certain conditions the leading edge of the plasma propagates away from the laser as an optical detonation where the leading shock front fully ionizes the background gas, and the inverse bremsstrahlung absorption zone immediately behind it is equivalent to the chemical energy release zone in an ordinary detonation. The front velocity is Vod =(3Ei/m)1/2, where Ei is the ionization (and dissociation) energy. This velocity is in agreement with experiments and with certain stability considerations. Radial expansion takes place immediately behind the detonation front and reduces the density to about one-third of the initial filling gas density. Far behind the leading edge the laser-produced plasma acquires an equilibrium radius R and steady pressure, density, and temperature determined by a balance between laser energy absorption and conduction and radiation losses. The density profile maintains a shallow minimum on axis.

Chemical nonequilibrium effects in hydrogen-air laminar jet diffusion flames

A theoretical medel for the structure of hydrogen-air laminar jet diffusion flames has been developed. The model includes the effects of nonequilibrium chemical kinetics and realistic transport properties. The reaction zone in such flames is found to resemble the recombination zone in premixed flames. Distributions of the free radicals H, O, and OH are substantially in excess of local equilibrium values. The computed results show that the partial equilibrium approximation, which is often employed in premixed flames, is valid within the reaction zone but breaks down outside it. Hydroperoxyl is found to be an important intermediate species in the flame, being formed primarily by the reversible recombination reaction H + 0/sub 2/ + M ..-->.. HO/sub 2/ + M and destroyed by H, O, and OH radical attack. The absence of chemical equilibrium and the broadening of the energy release zone result in peak temperatures which are well below the adiabatic flame temperature. Broadening of the energy release zone is due significantly to the mobility of hydrogen atoms.

Self-similar problem of the motion of a plane layer of heated material with an arbitrary equation of state

The self-similar problem of the nonstationary motion of a plane layer of material in which energy from an external source is released for values of the flux density q0 on the boundary which are constant in time is considered. The self-similar variable is μ = m/t, where m is the Lagrangian mass coordinate and t is the time. The characteristic values of the velocity, density, and pressure do not vary with time. For a self-similar problem the energy flux density q must also depend only on the self-similar variable. In this case q(μ) can be an arbitrary function of its argument and can be given by a table. Examples are presented of actual physical processes in which the mass of the energy-release zone increases linearly with time. The equation of state can have an arbitrary form, including specification by a table. The gaseous state of matter for an arbitrary variable adiabatic exponent, the condensed state, and a two-phase state can be described. A solution of the self-similar problem is presented for the heating of a half-space bounded by a vacuum for a certain specific equation of state and various flux densities q0 and velocities M of the advance of the energy-release zone.