A kinetic mechanism of oxidation and combustion of CH3CHO - O-2 mixtures is proposed. Calculations by this mechanism of oxidation and two-stage self-ignition of acetaldehyde - oxygen mixtures fit the available experimental data quite satisfactorily. The kinetic mechanism is used to depict propagation of a steady cool flame in this mixture. The cool flame model suggested is shown to be valid for practical computations.
Results of detailed calculations of combustion in a wake behind a bluff body are presented and a flame stabilization criterion is formulated. According to this criterion, a flame is blown off from the flameholder at a Michelson number value less than unity, i.e., when the burning time of a particle moving along the limiting trajectory in the recirculation zone exceeds the time of particle journey to the turning point of the limiting trajectory. The calculated limiting velocity at which a stoichiometric methane-air flame is stabilized agrees satisfactorily with the available experimental data. It is shown that as the ratio of channel blockage by the flameholder changes, the range of stable combustion varies nonmonotonically, namely, there is an optimal flameholder size at which the best stabilization parameters are achieved. This result is also consistent with experimental observations.
The limits of the recombination front propagation through a system with frozen radicals are studied, assuming two recombination channels, mechanochemical and diffusion-controlled The results of the study are used to analyze of experiments with irradiated materials.
A mathematical model for the process of friction-induced heating at a nonideal thermal sliding contact is formulated. An analytical method is proposed for solving the corresponding mixed nonstationary equations of heat conduction. At the heart of the method is the idea of splitting the kernel of a singular integral Fourier transformation with respect to the spatial coordinate. Theoretical results are used to assess the effect of deterring additives on the friction-induced heating of energetic materials.
The problem on propagation of an elastic compression wave in a disintegrating brittle material is solved analytically. It is believed that a destruction wave propagating with a subsonic velocity behind a shock wave is initiated at the impacted surface. Disintegration of the material is modelled as relaxation of sheer stresses behind the destruction-wave front. The kinetic parameters of destruction are correlated with the compression-pulse structure.
We present a method to calculate a detonation Hugoniot directly from piston-driven molecular dynamics simulations without determination of the equation of state. A model system that exhibits a chemically sustained detonation is investigated. The front velocity derived from the detonation Hugoniot is in excellent agreement with that obtained directly from an unsupported molecular dynamics simulation.
The paper describes a solution of three dimensional unsteady problems in the field of compressibe fluid dynamics. A similar procedure to that adopted in two dimensions is used whereby one starts on a Lagrangian code and changes over to an Eulerian one when the motion of the fluid becomes such as to give significant mesh distortion. For the Lagrangian calculations reported here, the DYNA3D program from Livermore has been used. At a suitable time the calculation is transferred to an Eulerian code, NUTMEG, written by the authors. A key feature of this code is the interface tracking procedure which has successfully been applied to complex problems involving many material interfaces. The main features of NUTMEG are described and examples are given of the use of the Lagrangian/Eulerian procedure.
Typical for a multicomponent reacting gas is its breaking into subsystems with different temperatures. Consistent modelling of equilibrium and kinetics in a chemically reacting multitemperature gas is carried out assuming constant temperatures of the subsystems. An equation for the equilibrium law of mass action and the corresponding expression for the equilibrium constant of an arbitrary chemical reaction are derived. The familiar relationship available from thermodynamics of irreversible processes is established between the reaction rate and its chemical affinity in the nonequilibrium stage of reagent conversion. The expression relating the rate constants for direct and reverse reactions is presented. An alternative form of the set of differential equations of gas-phase chemical kinetics is proposed.
Nonideal properties of detonation of aluminum-containing explosive formulations including possibility of occurrence of the aluminum oxidation reaction in the rarefaction wave downstream of the Chapman-Jouguet plane are traditionally accounted for by different time scales of high explosive (HE) decomposition and Al oxidation. However one has to keep in mind an important fact that the energy increase due to aluminum oxidation is accompanied by formation of products containing a smaller amount of gaseous components and that their ability to convert the energy released into work is less. In the first part of the paper which critically analyzes the contemporary notions of aluminum behavior in detonation of condensed high-explosives we demonstrate the effect of this behavior on the traditional estimates and interpretation of investigation results. In the second part we consider the conditions at the Chapman-Jouguet plane in a steady detonation wave that unexpectedly arise due to this effect. In the third part, a theoretical model in which Al consumption in a detonation wave is controlled by mixing (diffusion) of disperse Al and products of HE decomposition.
The results of dynamic mass spectrometric studies of the composition of the gas-phase products formed in a wave of solid-phase burning spreading through Mo + B, Nb + B, and Ta + C SHS systems show that concentrations of boron and carbon oxides and suboxides vary periodically with frequencies corresponding to pulsations of burning waves in these systems known from previous investigations. A kinetic structure of the combustion wave is analyzed to demonstrate that self-sustaining oscillations attributed previously to thermal instability can be interpreted within a kinetic model of a multistage process involving gas-phase transport of reagents.
It is shown that there is a negative feedback in the "ozone layer-UV radiation at the surface-oceanic phytoplankton system, which partly compensates for ozone layer depletion caused by anthropogenic or natural factors. To make a long story short, the mechanism of this phenomenon lies in the fact that ozone layer depletion and subsequent rise of the UV-radiation level at Earth's surface conduce to destruction of a portion of oceanic phytoplankton with the result that the flow of carbon dioxide to the global ocean reduces, and accordingly, the carbon dioxide content of the atmosphere increases. This, in turn, promotes build-up of atmospheric ozone, thus compensating in part for its initial loss. Quantitative data on the efficiency of the aforesaid mechanism were gained by computer simulation of processes in the middle atmosphere using a two-dimensional radiation-convection model and from the literature. It has been found that in the case of initial ozone layer depletion by 16% accompanied by a 5% loss in the phytoplankton content and by a decrease in the CO2 flow to the ocean of 5 Gt C per year, the feedback mechanism can compensate for 4.7% of the initial ozone loss in 20 years and for 9.4% in 50 years. An increase in Earth's surface temperature calculated under the same conditions was 0.33 K.
The effect of photoinduced dipole interactions between atoms on the adsorption kinetics and transport processes on a surface are studied within the average field approximation. Adatom migration processes under an inhomogeneous distribution of the external electromagnetic field intensity are analyzed. The feasibility of governing the kinetics of surface phenomena is demonstrated.
Formation of dioxins in burning of chlorine-containing coals in thermal electric power stations (TES), their spread in smoke plumes of TES, destruction by photochemical reactions, and build-up in the surface Earth layer are studied.
The effect of collisions on orientational relaxation of photodissociation-induced anisotropy in an ensemble of photofragments in gas phase is analyzed. Consideration is being given to the most general case, when initial molecules and photodissociation fragments can be approximated by asymmetric tops. The adopted dynamic model of collisions represents a "linear combination" of the model for J and E diffusion. General expressions for rotational and orientational correlation functions (CFs) are derived assuming an arbitrary (nonequilibrium) initial distribution of fragments over angular momentums. An explicit expression for this distribution is derived assuming instantaneous dissociation. Orientational CFs are obtained in the analytical form in the limits of rare (rarefied gas) and frequent (diffusion limit) collisions and at short times. It is shown that in certain cases, the characteristic frequencies of damping of rotational and orientational CFs are independent of the photodecomposition mechanism and depend solely on the collision dynamics, while the effect of photofragmentation is allowed for in the time-independent coefficients appearing in the expressions for CFs.
Based on the body of experimental data on crystalline quartz modifications, shock wave and static compression of quartz of various density, expansion isentropes, and rheological properties of silicate melts a critical analysis of available diverse (sometimes contradictory) standpoints on the nature of the high-pressure quartz phase formed behind shock waves and on the mechanism of its formation is carried out. The most reliable inferences from the reviewed studies are formulated.
Vibrational and orientational relaxation of nonassociated alcohol molecules (CH3OH, CH3OD, C2H5OH, C3H7OH, and C4H9OH) in dilute CCl4 solutions is studied by analyzing the shape of Raman scattering and IR absorption bands due to nu(OH) vibrations. Time correlation functions (CFs) for vibrational relaxation, orientational CFs of dipole moment, polarizability tensors for RS, and their correlation times are calculated. It is found, how the times of phase and orientational relaxation (tau(upsilon) and tau(1R)) and the mechanism of orientational motion of alcohol molecules vary with molecular size and structure.
A clusterization criterion (lack of clusters) for a high-temperature oxidation reaction in the C2B4H6/H2O system is suggested. Regions in the P-T plane are ascertained where no clusters form in the course of oxidation or oxidation is preceded by carborane conversion into clusters. Pressure and temperature ranges are found where the oxidation times of a stoichiometric C2B4H6/H2O mixture do not exceed 1 ms.
