Home – Home – Jornals – Combustion, Explosion and Shock Waves 2020 number 3

A reaction model is proposed for calculating the process of ignition of diborane mixtures with air. The model summarizes the previously developed kinetic models of oxidation of diborane, boron, as well as lower oxides and hydroxides of boron. A distinctive feature of the model is the use of physically grounded rate constants of the most important reaction channels, which were either computed or derived from available experimental data. The mechanism is tested against experimental data on the diborane ignition delay and flame velocity in diborane-oxygen and diborane-air mixtures. The results predicted by the proposed model are found to be in reasonable agreement with experimental data. The model can be used for engineering calculations and also for numerical simulations of diborane combustion in lean and stoichiometric mixtures with air.

Combustion and ignition processes are considered from the standpoint of the theory of thermal ignition and reaction kinetics. An analytical solution of the problem of thermal hotspot ignition was obtained to describe the ignition processes reactive gas mixtures. As a result of this solutions, the critical conditions and the ignition induction time were determined. A solution of the problem of ignition of a methane-air mixture characteristic of the conditions of mine workings.

The formation and dynamics of a spherical gas bubble »1 nm - 1 <&mu;>m) in the liquid gasification zone of a solid high-energy material at high pressures is theoretically investigated. A simple model is proposed in which all thermodynamic parameters with the exception of fluid pressure and fluid velocity are independent of spatial variables. The stationary radius of bubbles decreases as pressure rises, but the stationary state is unstable: large bubbles grow relatively slowly and a thermal explosion subsequently occurs in them, with small bubbles quickly vanishing.

The work presents a simplified algebraic model for calculating the OH*, CH*, and CO*2 concentrations within the context of reduced propane flame oxidation treatment. Excited and precursor species are obtained through post-processing of the basic simulation results, employing well-established quasi-steady state expressions produced from the detailed chemiluminescence kinetics. Inaccuracies introduced in these derivations are compensated by applying correction functions fitted by comparing model computations against detailed chemistry results. The formulation is tested in a range of laminar flames to determine its suitability for extension into turbulent flame simulations.

Evaporation of a water-methanol solution droplet is experimentally studied. This process is mathematically modeled. Based on the results of a comparative analysis of the results of physical and numerical studies, the parameters of the evaporation of a water-methanol solution droplet are determined for the purpose of using its combustion in mathematical modeling. The results of numerical studies of the combustion of a gas flame with the injection of the water-methanol solution droplets into it in an industrial plant are presented. These results satisfactorily correlate with experimental data.

The heat of combustion and enthalpy of formation of bis(4''-nitro[3,3':4',3'']terfurazan-4-yl)-diazene (DNFNF) and (bis(4''-azido-[3,3':4',3'']terfurazan-4-yl)-diazene (DAzFNF) were first experimentally determined. It is found that the energy increment of the substitution of the azide group for the nitro group in the furazan cycle averages 290 kJ/mol and is close to the increment of substitution of N₃ for NO₂ in trinitroethane. The dependence of the energy parameters of metal-free rocket propellants based on a mixture of ammonium perchlorate with DNFNF or with DAzFNF with an active binder on the content of the highly enthalpy component in the formulation was studied by thermodynamic analysis.

Synthesis is carried out in a Ti + Al mixture prepared by two methods, namely preliminary mechanical activation (MA) or preheating. Synthesis occurs in the cases of layer-by-layer combustion (SHS) and thermal explosion. The dependences of burning rates of activated Ti + Al mixtures on the MA duration are investigated. The relationships between the initial temperature and the rates and maximum combustion temperatures of initial mixtures along with the elongation of samples after combustion are determined. The phase composition of the initial mixtures after activation and of the synthesis products is described. The MA duration (12 min) at which the burning rate of the mixture is maximum is experimentally determined. For this mixture (12-min MA), the dependence of the burning rates and maximum combustion temperatures along with the elongation of samples after combustion on the initial temperature is studied. Synthesis at which the content of the main phases (TiAl and Ti₃Al) in the products is maximized is established.

Combustion and the formation of structures and phases in a 2Co-Ti-Al system during a self-propagating high-temperature synthesis process in a thermal explosion are under study. It is determined that a single-phase product (a Co₂TiAl Geissler compound) can be obtained in this system. Morphology, microstructure, and physical-magnetic properties of combustion products of the system are investigated.

In order to ensure the safety and reliability of weapons, it is very important to grasp the influence of the inside and outside diameters of the shell on the delay time. In this paper, a fluid-solid coupling model is established for a metal baffle-type delay element with a silicon-based delay composition. The combustion flow field of the delay element with the inside diameter of 3, 4, and 5 mm is simulated by the STAR-CD software. Then a new method is proposed to calculate the delay time of the heat conduction delay element. The influence of the internal and external diameter on the delay time of the thermal conduction delay element is studied. The results show that the temperature of the ignition composition gradually increases due to the heat conductivity of the metal baffle after burning of the delay composition, and the highest temperature is reached at the centre of the ignition composition. The influence of the size of the inside and outside diameters on the delay time has a critical equilibrium point, which may be related to the balance between the combustion heat increment and the heat loss.

The propagation of crown forest fires in the presence of fire breaks and barriers of finite sizes was studied by mathematical modeling. Mathematically, this problem reduces to solving the Reynolds equations for turbulent flow taking into account chemical reactions. The control volume method was used to obtain a discrete analog. The fields of temperature, concentrations of oxygen and volatile pyrolysis and combustion products, and volume fractions of the condensed phase were calculated. The model made it possible to establish the dynamics of the contours of crown forest fire spread, which depend on the amount and type of forest fuels, moisture content, wind speed and direction, etc. In addition, the dependence of the size of fire breaks and barriers on the above parameters for which the crown fire stops spreading was determined.

The initiation and stabilization of detonation combustion of kerosene vapor in a supersonic air flow entering an expanding axisymmetric nozzle with a coaxial central body is numerically studied. Calculations are based on a reduced kinetic model of combustion, which includes 68 reactions for 44 components. Enthalpy and entropy of components are determined using approximating polynomials from the NASA database. A hydrodynamic model is based on two-dimensional unsteady Euler equations for an axisymmetric flow of a multicomponent reacting gas. Calculations are performed using the Godunov finite-difference scheme and its -modification of improved accuracy on smooth solutions. The flow parameters that ensure the steady detonation combustion of kerosene vapor in the nozzle under consideration are determined. The detonation combustion of kerosene has a stronger thrust than hydrogen combustion, but is noticeably inferior with regard to specific thrust. The calculations are performed on the “Lomonosov” supercomputer at the Lomonosov Moscow State Universit.

The gas detonation of ethylene- and propylene-oxygen explosive mixtures in a wide range of equivalence ratio was studied. Detonation parameters were calculated using the DETON code. The experiments were conducted on an improved detonation bench in which the flow feed of the components of the explosive mixture and the intensification of the deflagration-to-detonation transition due to stratification of charges was implemented in an extended cylindrical channel using the CCDS2000 computerized detonation complex. Experimental data on the detonation velocity and size of the detonation front cell were obtained. The concentration limits of steady detonation in a cylindrical channel 26 mm in diameter were established. Using propylene and ethylene as fuel for detonation spraying, coatings of tungsten carbide with a cobalt binder and alumina were obtained and their properties are investigated. Coatings based on propylene with stratification of the explosive mixture charge, are comparable in properties and performance to coatings sprayed by dual-fuel (acetylene/propane) technology, which allows propylene to be considered as an acceptable fuel for detonation spraying.

To measure the temperature of the shaped-charge jet, three-layer copper-copper-Constantan liners consisting of a solid copper conical shell with an apex angle of 45 ^oC, a wall thickness of 1.5 mm and a pressed-in shell folded from a 1.0 mm thick copper sheet explosively cladded on the inside with a Constantan layer 0.5 mm thick. Then the Constantan layer was partially removed so that only the upper third of the inner surface of the shells remained coated with Constantan. The thickness of the Constantan layer was chosen so that the nose of the shaped-charge jet consisted only of Constantan, and the jet tail of copper, which was determined from a microsection of the recovered slug. As a result, a copper-Constantan thermocouple was formed. At the moment of collision of the bimetallic jet with a target, an oscilloscope measured a thermo-EMF signal. The obtained thermo-EMF corresponds to a temperature of 800 ± 80 ^oC.

The change in the structure of welds obtained using a new welding wire and subjected to high-velocity impact was investigated by optical and scanning electron microscopy and X-ray diffraction analysis. It is shown that after welding, a structure of martensite,  ferrite, and a metastable austenite is formed in the weld metal. Subsequent intense exposure leads to hardening of the weld metal due to the transformation of metastable austenite into strain-induced martensite. Kinetic microindentation of the welds was performed.