Mathematical modeling of the stripping of combustible forest materials by explosion of a cord charge

The stripping of combustible forest materials (thin twigs and needles) by explosion of a cord charge are studied by mathematical modeling of blast-wave propagation in a forest canopy for the placement of the cord charge at different heights. The calculation results allow one to reduce the consumption of explosives in extinguishing crown forest fires. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 92–99, May–June, 2006.     

Formulation and Solution of the Problem of Drying of a Layer of Combustible Forest Materials

The drying of combustible forest materials is the most important and least studied stage of the multiphase process of their burning under natural conditions. Physical and mathematical modeling of the drying of a layer of combustible forest materials is performed in a conjugate formulation by solving the equations of a binary boundary layer and the equations of heat and mass transfer in a layer of combustible forest materials with corresponding boundary and initial conditions. Solutions of this problem for diurnal and seasonal changes in environmental temperature are obtained for three scenarios of development of weather conditions. The data obtained are compared with experimental data on drying of needles of pine and some other coniferous trees. A rigorous physicomathematical basis for prediction of forest fires is given.     

Ignition of forests as a result of the explosion of the Tungusskii meteorite

Relying on the laws of the mechanics of multiphase reacting media, we construct a mathematical model of the ignition of forests by radiation emitted as a result of the explosion of the Tungusskii meteorite. The forest canopy is modelled by a multiphase porous reacting medium. The ignition regimes realized at different distances from the center of the explosion are analyzed. It has been established that the maximum radius of the ignition zone is 6–9 km for the forest canopy and 12–16 km for the ground cover, depending on the stock and moisture content of combustible forest materials. This corresponds to an explosion energy of 25·10¹⁶ J. V. V. Kuibyshev Tomsk State University, Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 6, pp. 8–14, November–December, 1993.     

Mechanism of formation of a heated ground layer by an intense air burst

A mathematical modeling study demonstrated the fundamental possibility of the formation of a heated layer (a meter-long layer of erosion vapor and air with temperatures of a few thousand degrees and a density 20–50 times lower than the normal air density) at the ground surface under the action of the long-distance traveling fireball radiation from an intense explosion at a moderate radiant flux density of about 1 GW/m² for a time of about 10 msec. The results of the numerical study agree with data from observations of the heated layer effect in nuclear-weapon tests. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 100–106, July–August, 2006.     

Experimental study of the thermal conductivity of heat insulation materials based on expanded vermiculite

Results are presented for experimental studies of the thermal conductivity of expanded vermiculite. Tests are performed in an experimental test unit by a steady-state heat flux. Thermal studies are carried out in the range 300–1100 K. It is shown that thermal conductivity increases uniformly with an increase in temperature. The most probable reason for an increase in thermal conductivity is the effect of heat radiation. Results are provided for an approximate second power polynomial. __________ Translated from Novye Ogneupory, No. 11, pp. 41–43, November 2007.     

Ignition of a layer of combustible forest materials

Theoretical and experimental studies of the ignition of forest combustible materials by real ignition sources, which are modeled by a reference source, are reported. The time of ignition by the reference source is determined. The critical ignition energy is estimated, and its variation under real conditions is analyzed. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 6, pp. 14–22, November–December 1998. The paper is reported at the 2nd International Conference on Forest Fires (Irkutsk, 10–15 June, 1997).     

Flameproofing modification of synthetic materials by laser radiation

A method of giving flameproof properties to materials and articles in light industry by modification with phosphorus-containing flame retardants under the effect of the energy from CO₂ laser radiation was developed. The optimum modification parameters (LR power density of 5.3 W/cm², treatment time of 30 sec, concentration of flame retardant (FR) in 5–10% solution, impregnation time of 100–120 sec), which allow obtaining flameproof materials with high performance properties were determined. The oxygen index of the cloth increased to 29.5–42%, the breaking strength increased by 8.5–21%, and the abrasion resistance increased by 5–12% without worsening the hygroscopicity and air permeability. The activating effect of laser radiation on the modification process was demonstrated; it resulted in an increase in the sorption capacity of the fibre structure of the materials, diffusion of FR into the bulk of the fibres, uniform distribution of the fibres in the form of finely disperse particles, intensification of the reaction of the components, ordering of the structure, and improvement in the physicomechanical properties of materials and articles in light industry. The method saves on expensive raw materials — flame retardants — due to conducting the modification from low-concentration solutions and allows expanding the line of flameproof materials. __________ Translated from Khimicheskie Volokna, No. 1, pp. 48–52, January–February, 2008.     

Needle-punch materials with high compressive strength

Incorporation of a bicomponent fibre in needle-punch materials and then treating them with heat by different methods results in a significant increase in their compressive strength. The compressive strength of needle-punch and modified materials is a function of the size and orientation of the fibre bundles. Increasing the needle-punching density does not significantly increase the compressive strength of the materials. __________ Translated from Khimicheskie Volokna, No. 5, pp. 34–36, September–October, 2007.     

Ignition of Combustible Forest Materials by a Radiant Energy Flux

The paper reports results of experimental ignition of litter layers consisting of needles of cedar, pine, and fir-tree, birch leaves, lichen (Cladonia), and moss (Pleurozium shreberi). It is established that the moss is ignited faster than the other combustible forest materials. It is shown that with equal moisture contents, the ignition times of needle litter from different trees are identical within the experimental error, and for litter of birch leaves, the ignition time is shorter than that for litter of coniferous trees. This difference is found to be due to differences in the interaction of the radiant flux with litter layers of needles and leaves. Minimum values of the ignition heat pulses for needle and leaf litter layers are estimated for various heat-flux densities. These values tend to a minimum for a heat-flux density of 0.5–0.8 MW/m².     

Flame propagation in chlorine-containing combustible systems under ignition by a constant light beam

The action of the light emission of a mercury—quartz lamp on combustible mixtures of chlorine and difluoromethane and hydrogen at atmospheric pressure increases the upper concentration limit of flame propagation and flame velocity in mixtures similar in concentration to the upper concentration limit, because, during flame propagation in these mixtures, the rates of the thermal and photochemical dissociation of chlorine molecules are comparable, and the chlorine concentration behind the flame front is minimum. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 3–8, January–February, 1998.     

Effect of periodic perturbations on the thermal decomposition of some composite materials

Experiments indicate that the thermochemical decomposition of composite materials is sensitive to small periodic perturbations in the external flux and to wall vibrations. Stable, unstable, and self-oscillatory combustion regimes are found for these materials, and limiting conditions for the binder concentration and vibration intensity are determined for which it is possible to reduce thermal loads to the wall and control heat and mass transfer. Monostationarty and stability boundaries are constructed and the results are compared with theory. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 67–73, May–June 1999.     

Explosive decomposition of slightly compacted powders of lead azide over a wide range of laser pulse length

Abstact  Initiation of slightly compacted powders of lead azide of density not greater than 1.2 g/cm³ by laser radiation with a wavelength of 1.06 μm was studied experimentally over a wide range of pulse lengths (10⁻⁵–10⁻³ sec). It is shown that the ignition threshold of the slightly compacted samples does not change as the laser pulse length is increased. It is found that the explosion products contain molten lead particles whose sizes are an order of magnitude larger than the sizes of similar particles from explosion of samples of density 4.0 g/cm³. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 98–100, September–October, 2008.     

Modification of reinforced thermosetting plastic with ultraviolet radiation

Curing of filled systems previously treated with UV radiation is a first-order process with respect to the oligomers that takes place in the diffusion region. The slowing effect of viscose fibres in the initial stage of curing increases the impact strength of the reinforced material. The UV radiation increases the probability of linear chain growth during curing and results in material with a high average weight of crosslinked chains. UV treatment increases the impact strength and static bending breaking stress by 20–50% in comparison to materials obtained without irradiation and is an effective method of modification. The polymer reinforcement decreases the density and increases the strength characteristics of concrete articles in comparison to unreinforced concrete. __________ Translated from Khimicheskie Volokna, No. 1, pp. 45–48, January–February, 2008.     

Approximate method for solving problems of ignition theory

A method is proposed to determine the moment of ignition of a semi-infinite massif of a condensed material exposed to an external heat flux specified as an arbitrary function of time. The method uses the fractional-differentiation formalism. For large values of the heat flux, the calculation results coincide with the results obtained using well-known methods. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 23–28, March–April, 2006.     

Effect of a heat-conducting element on the gasless combustion of cylindrical samples under nonadiabatic conditions

The effect of a heat-conducting element on the ignition and combustion of a cylindrical layer of a gasless mixture with a nonadiabatic lateral surface is studied. It is shown that the introduction of an element with high heat conductivity allows one to extend the region of ignition of the gasless composition by a heated surface and to increase burning rate under conditions of external heat release. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 66–71, January–February, 2007.     

Surface temperature measurements on burning materials using an infrared pyrometer: accounting for emissivity and reflection of external radiation

This paper demonstrates the successful use of an infrared pyrometer, operating in the 8–10 µm wavelength band, to measure the surface temperature of combustible specimens in a heat release calorimeter. The temperature histories of ten different materials were measured in the ICAL (intermediate scale calorimeter). The set of materials comprised four wood products, gypsum board, polyisocyanurate foam, PVC floor tile, PMMA and two non‐combustible boards. A small‐diameter bare thermocouple was installed on each specimen in order to determine an accurate temperature for comparison. The spectral emissivity and the spectral flux reflected from the surface were measured simultaneously and used to correct the apparent temperature measured by the pyrometer. The spectral emissivity and reflected spectral flux were both constant prior to ignition for all the combustible materials. During the burning phase all the combustible materials had a spectral emissivity very close to unity. The agreement between the temperatures measured with the pyrometer and thermocouple was not affected by the flame. The wood products, the polyisocyanurate foam and the calcium silicate board required no correction for reflected spectral flux over the whole temperature range. Copyright © 2004 John Wiley & Sons, Ltd.     

Polyethylene with low combustibility for construction applications containing chemical fibres and disperse fillers

The studies demonstrated the possibility of practical implementation of a method of fabricating difficultly combustible polyethylene by incorporating chlorinated paraffin stabilized with CaCO₃ and fireproof fibres in the polymer. The PCM based on the modified polyethylene have high physicomechanical characteristics and low combustibility, which places them in the class of construction materials for engineering and technical applications. Engels Engineering Institute, Saratov State Engineering University. Translated fromKhimicheskie Volokna, No. 6, pp. 46–49, November–December, 1999.     

Spinning of oxide fibres made of natural cellulose materials

The possibility of obtaining high-melting fibre materials from plant fibres and textile production wastes containing 40–60 wt. % cellulose was demonstrated. The optimum conditions of preliminary chemical treatment of natural raw material to increase the sorption capacity of the materials were determined. The conditions of heat treatment of salt-containing natural fibre materials which would allow regulating the crystal and pore structure of oxide fibres were established. Translated from Khimicheskie Volokna, No. 5, pp. 27–31, September–October, 1997.     

Characteristics of HMX combustion waves at various pressures and initial temperatures

Temperature profiles and combustion-wave parameters are obtained experimentally for combustion of pressed HMX at room temperature and pressures of 1–500 atm and in the case of a change in the initial temperature of the specimens from −170 to +100°C at pressures of 1–75 (90) atm. The following combustion-zone parameters are determined: the heat effect in the c-phase, the heat transfer from the gas to the c-phase by thermal conduction and radiation, the rate of heat release in the gas near the surface, and the dimensions and temperature of the combustion zones. The authorsé previous conclusion that there is one process of decomposition and evaporation of HMX during its gasification in the condensed-phase reaction layer of the combustion wave is confirmed. Dependences of the fraction of decomposed HMX on the initial temperature of the specimens and the pressure are obtained. The differential characteristics of the combustion rate, surface temperature, and radiative heat transfer, required for the nonlinear theory of HMX combustion stability, are evaluated. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 59–66, March–April, 1998.