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).     

Ignition of aluminum powders mixed with liquid hydrocarbon fuels in air

The feasibility of ignition of aluminum powders in air is studied by examining a number of hydrocarbon fuels, promoter additives in them, and hybrid systems of liquid mixtures and powders in shock waves. Data are obtained on the ignition delays for each of the components and mixtures of them. It is shown that for temperatures of 1000–2000 K, ignition is possible, with delays of less than 2 msec, in hybrid systems of Al powders having a dispersity of 5–10 μm with diesel fuel and added fatty-alcohol nitrates. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 35–40, January–February 1999.     

Behavior of the temperature and burnup of a reactive body at the surfacex=0 upon thermal ignition

Using the Laplace transform, we show that equations that govern the evolution with time of the temperature and burnup of areactive body in the cross sectionx=0 in the processes of thermal ignition can be derived. The equations for the temperature and burnup of a semibounded body at the ignition pointx=0 are obtained when the ignition is initiated by a radiation flux and in the case of thermal explosion, of a hot spot. An asymptotic analysis of the equations obtained is carried out, and the ignition times of bodies and the critical conditions for ignition of a hot spot are determined. Vilyunov's “adiabatic method” of obtaining the temporal ignition characteristics is justified. The results of the asymptotic analysis of the ignition of a hot-spot are supported. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 46–54, September–October 1999.     

Hydrodynamic effect of an electrical explosion on the ignition of condensed materials

The ignition of condensed materials by an electrical explosion is studied numerically. The effect of the wave process in the sample on its ignition characteristics is analyzed. Calculated values of the ignition time are given for various sample layouts, sample dimensions, and parameters of the initiating pulse. The effect of the hydrodynamic process caused by an electrical explosion in a condensed reactive material on the ignition period is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 15–22, January–February, 2007.     

Ignition of porous materials by gas filtration (unsteady downstream filtration)

The wave theory of ignition is used to create an analytic method for calculating the temporal characteristics of ignition in porous samples by a flow of hot gas into the material (unsteady downstream filtration). When classical dimensionless variables are used, characteristic ignition times are found to have an anomalous dependence on the parameter β=RT _ign/E: as β is increased, the duration of the ignition stages is reduced and does not increase, as it does for conductive heating of the material. A scale is found for the gas density, such that the temporal ignition characteristics have the customary dependence on β when it is used. It is shown that the equations for isothermal filtration can be used to determine the mass feed rate of the gas. Numerical calculations confirm the validity of the basic assumptions of the theory regarding the existence of stages in the ignition process and the wave mechanism for heating the material. Good quantitative agreement is obtained between an approximate analysis and the numerical calculations. The error in determining the time to develop a zero temperature gradient at the sample boundary and the thermal explosion time is less than 50%. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 49–59, January–February 1999.     

Transitional regimes of wave propagation in metastable systems

Results of a theoretical study of deflagration-to-detonation transition processes in hydrogen-air mixtures are presented. The dependence of the deflagration-to-detonation transition scenario on the governing parameters (initial temperature of the mixture, ignition energy, ignition time, geometric characteristics of cavities, and distances between cavities in the ignition zone) is considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 25–37, September–October, 2008.     

Kinetic mechanism of propane ignition and combustion in air

A detailed kinetic model of propane ignition and combustion in air is developed. The model includes 599 reactions with 92 species and involves both the high-temperature and low-temperature mechanisms of oxidation. The model is tested against experimental data on the ignition delay time, on propane conversion during low-temperature oxidation, on changes in species concentrations during propane pyrolysis, and on laminar flame propagation velocity. The model is tested in wide ranges of the initial temperature T ₀ = 680–1900 K, pressure p ₀ = 0.17–30 atm, and fuel-air equivalence ratio ϕ = 0.13–2.     

Self ignition in laminar mixing layer

Boundary layer equations are used to study ignition in laminar mixing layers. Under a number of assumptions, analytic solutions are obtained. Calculations based on the resulting equations and formulas, and on a boundary layer model, are found to be in good agreement. The general behavior of ignition in mixing layers is studied. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 27–34, January–February 1999.     

Calculation of the ignition of a condensed material by a hot wire

Approximate analytical solution and numerical calculations of the ignition of a condensed material (CM) by a wire heated by direct electric current are used to study the effect of electrophysical characteristics and geometrical dimensions of the conductor and the thermokinetic properties of the solid fuel on the ignition delay. The results obtained are in satisfactory agreement with experimental data. Results of parametrical analysis are generalized by an interpolation formula. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 4, pp. 58–62, July–August 1999.     

High-temperature ignition of a reactive material by a hot inert particle with a finite heat reserve

The initiation of a reactive material by an inert particle at a high initial temperature and with a limited heat reserve is studied numerically. The possibility of using known ignition criteria to study the process are analyzed. The effect of burnout on high-temperature ignition by a particle with a limited heat reserve is studied. Four regimes of the process and the critical parameters separating these regimes are determined. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 40–47, March–April, 2008.     

Ignition and combustion of magnesium particles in a nonuniform thermal field

A distributed two-dimensional mathematical model of ignition and combustion of magnesium particles with allowance for the heterogeneous chemical reaction and for the region of the thermal influence of the particle on the gas is developed. Problems of particle ignition under the action of uniform and nonuniform thermal fields in a rectangular microchannel are solved. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 48–57, March–April, 2008.     

Ignition of a system of hot spots in the presence of heat transfer through the side surface

An asymptotic analysis is used to study the ignition of a reactive cylindrical body in which, initially, there is a periodic system of hot spots. The effects of the heat transfer through the side surface of the cylinder and the adjacency of hot spots on the ignition regimes are studied. The solution shows that the critical ignition conditions depend considerably on the heat-transfer regime. The adjacency of the hot spots leads to finite changes in the parameters only if they are sufficiently close to each other. The results obtained for a heat-insulated side surface are compared with known solutions. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 17–21, March–April, 2000.     

Experimental studies of the ignition of a solid propellant in water

The ignition of a solid propellant in water by means of an unsealed system of ignition in the form of an open channel with a heating coil placed in the channel is considered. The ignition system operates according to the principle of creation of extreme conditions of water boiling in the channel with heat supply from an electrical heater. It was established visually that the heating of the walls is preceded by a preliminary period connected with the change in the state of aggregation of water. The system was tested on solid-propellant specimens. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 52–57, July–August 1999.     

Hot-Spot Ignition of a Reactive Gas in an Inert Porous Medium

The main stages of development of hot-spot ignition of a reactive gas in a high-porous medium with high values of the Peclet number under conditions of natural gas filtration and limited internal heat transfer between the phases are determined. Gas ignition in a U-shaped hot spot is considered within the framework of an asymptotic analysis with high values of the temperature difference and Frank-Kamenetskii parameter. The critical relation of parameters separating the regimes of gas ignition and gradual cooling of the hot spot is determined. The dependence of the ignition time on parameters of the process is found and analyzed. A strong effect of interphase heat transfer on the ignition limit and time is demonstrated. An example of calculating the critical parameters of hot-spot ignition of methane in processed rocks is given. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 41–48, September–October, 2005.     

Numerical study of heat waves in the oxidation of a magnesium wire

A mathematical model of ignition of magnesium samples is proposed based on the concept of the existence of thermal deceleration of a chemical reaction responsible for ignition. The model gives realistic values of temperatures after sample ignition and is in satisfactory agreement with experimental data on the dependence of the radius of a small particle on the limiting temperature of the ambient medium. It is shown that heat waves can be excited by heterogeneous oxidation of Mg wire located in the external flow. The range of parameters in which self-excited wave regimes are observed fits experimental data on oxidation of metal wires qualitatively and in order of magnitude. The problem of initiation of an ignition wave by the initial distributions of the sample temperature is solved numerically, and the stability of heat waves to small and finite perturbations is shown. Tranlated fromFizika Goreniya i Vzryva, Vol. 34, No. 6, pp. 29–38, November–December 1998.     

Effect of pressure on the ignition temperature of compact samples of nickel alloys in oxygen

It is found that compact samples of nickel and its alloys heated in “cold” (323 K) and “hot” (≤1573 K) oxygen ignite at temperatures exceeding the melting point of the materials. The ignition temperature is independent of the oxygen pressure up to 70 MPa. It is suggested that the drop in the ignition temperature of alloys with rising oxygen pressure reported in several papers is related to systematic errors in measuring the surface temperature of the samples. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 2, pp. 54–58, March–April 1999.     

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.     

Filtration combustion of porous metallic samples in a gas diluted by an inert component

Filtration combustion of a porous layer with natural filtration of the oxidizer diluted by an inert component is studied. The problem of ignition of a porous layer by a heated surface permeable for the gas is solved, and the time of ignition is determined as a function of pressure in the reactor and initial porosity of the sample. Formation of an inert gas “plug” preventing chemical interaction is examined. It is shown that the mean depth of conversion of the condensed reagent in the porous layer depends on the sample length, porosity, pressure of the gas mixture, and concentration of the inert component. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 73–79, January–February, 2008.     

Ignition of model composite propellants by a single particle heated to high temperatures

This paper describes the technique and results of an experimental study of the ignition of condensed materials (model composite propellants) by a hot single metal particle. The dependence of the ignition delay of condensed materials (CMs) on the initial particle temperature is investigated. The mechanism of interaction of a single particle heated to high temperatures with unmetallized and metallized CMs is analyzed. It is found that the presence of a metallic filler in the CM changes the absolute values of the ignition delay and the relative characteristics of their spread. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 54–57, September–October, 2008.