Ignition of gaseous suspensions in an interacting continuum regime

A mathematical model is proposed for describing the flow of a mixture of gases and reactive solids including a heterogeneous chemical ignition reaction. The model is closed with an equation for the kinetics of oxide film growth. It is assumed that the heat of the chemical reaction can be released in both phases depending on the accommodation coefficients. The ignition of a motionless cloud of magnesium particles is studied in terms of this model. The model is tested with the use of experimental data on the maximum temperature of the medium as a function of the particle radius. Data on the dependence of the parameters of a heated particle cloud on the physical and chemical constants of the mixture and particles are presented. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 4, pp. 57–64, July–August 1998.     

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.     

Mathematical model of magnesium ignition in an extended range of parameters

A mathematical model of ignition of a magnesium particle with allowance for a heterogeneous chemical reaction is proposed. The model allows the final particle temperature after its ignition to be found and takes into account the region of the thermal influence of the particle on the gas. A stationary solution is found, which makes it possible to propose a classification of the thermal history of the particle-gas system. The mathematical model is consistent with experimental data on the dependence of the ignition delay on the gas pressure and particle radius and on the dependence of the limiting temperature on the particle radius and the ambient pressure. The mathematical model also reveals the effect of the size of the gas layer around the particle on the integral parameters of ignition. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 64–71, September–October, 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.     

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, extinction, and thermal hysteresis of a heterogeneous exothermic reaction

Critical conditions of ignition and extinction are studied theoretically for the case of a heterogeneous exothermic reaction proceeding on the uniformly accessible surface of a channel or a pore. Particular emphasis is placed on the thermal-hysteresis effect of the reaction (an ignition temperature in excess of the extinction temperature), which ensures stability of the reaction against changes in the external conditions. A model for the process is proposed and substantiated. It permits one to analyze the main regularities of the thermal reaction regime with allowance for the distribution of heat flows from the reaction zone to the reaction medium and the channel wall. The dependence of the critical conditions of ignition and extinction on the rate constants of heat release, the reaction order, and the thermal and geometric characteristics of the system is established. A rule is proposed that permits evaluating the effect of heat losses on the critical phenomena and the thermal hysteresis of a reaction on a cooled surface in the case where the critical conditions for the reaction on an adiabatic surface are known. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 51–58, March–April, 1998.     

Ignition and transition to unsteady combustion of metallized composite systems

Some additional relations for the previously published mathematical model are obtained. They allow one to take into account heat release from agglomerates of metal particles burning in the reacting layer of a composite propellant in a vapor-gas state. The results of numerical calculations of ignition and transition to combustion for a composite propellant with variation in the ratio of the components and parameters of the ambient medium are given. Institute of Applied Mathematics and Mechanics at Tomsk State University, Tomsk 634050. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 73–87, January–February, 1997.     

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.     

Conjugate mathematical model of ignition of magnesium samples

A distributed mathematical model of ignition of a magnesium particle with allowance for the heterogeneous chemical reaction and the region of the thermal influence of the particle on the gas is developed. A solution of the problem in a steady formulation is found, which allows expanding the classification of the thermal history of the particle-gas system. A numerical model for solving the considered class of boundary-value problems of magnesium-particle ignition is proposed, and the mathematical model is verified in terms of the ignition delay as a function of the Nusselt number. A limiting size of the gas layer near the particle, which determines the ignition mode, is identified. Stability of some heating regimes to finite and infinitesimal disturbances is demonstrated. It is shown that the ignition process can be controlled by a high-frequency thermal action on unstable states of the particle-gas system. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 57–63, May–June, 2006.     

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.     

Influence of liquid hydrocarbons on the ignition of metal powders in shock waves

Ignition of mixtures of metal powders with liquid hydrocarbon fuels in an atmosphere of pure oxygen and air behind reflected shock waves is studied experimentally. It is shown that the ignition delays for the mixtures are determined by the liquid phase, and the times of combustion are primarily determined by the particle size of the solid phase. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 108–113, March–April, 1998.     

Experimental and theoretical study of the ignition and combustion of an aerosol of encapsulated aluminum particles

This paper presents the results of an experimental study of the effect of particle encapsulation on the main operating parameters and features of the ignition and combustion of aluminum particles in air. It is found that the application of a nickel-based coating to the aluminum-particle surface, which substitutes for the oxide film, increases the reactivity of the aluminum-air mixture, with retention of the initial particle dispersity and energy parameters of the mixture. The model developed for the encapsulated-particle ignition taking into account the stress-strained state of the particle was used to determine the time and temperature limits for the retention of the protective-coating properties and to explain the experimental results. Bauman State Technical University, Moscow 107005. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 60–68, January–February, 1997.     

Ignition, combustion, and agglomeration of encapsulated aluminum particles in a composite solid propellant. I. Theoretical study of the ignition and combustion of aluminum with fluorine-containing coatings

This paper gives a brief review of methods for modifying metallic fuels for composite solid propellants, including the application of coatings onto aluminum particles (encapsulation). Requirements for the coating material are formulated. By means of thermodynamic calculations, it is shown that some fluorine-containing coatings reduce the content of the condensed phase in the propellant combustion products without decreasing the specific impulse. A mathematical model for the ignition of a single encapsulated particle is proposed. Calculations show a decrease in the ignition time of an aluminum particle with a fluorine-containing coating. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 46–55, September–October, 2006.     

Experiments and Numerical Calculations on Laser‐induced Ignition of Single Micron‐sized Aluminum Fuel Particle

This paper presents the experiments and numerical calculations on the laser‐induced ignition of single micron‐sized aluminum particle in an atmospheric pressure air flow at low Reynolds number. Experimental results demonstrate that the radiation intensity of single micron‐sized aluminum particle, during ignition, experiences first sharp rising, stable equilibrium and second steep rising stages. A simplified analytical model was built and numerically solved. Numerical results show that the three distinctive stages represent the heating, melting and evaporation, respectively. Laser radiation mainly contributes to heat aluminum particle, leading to phase transition (melting). The heat released from heterogeneous surface reaction (HSR) dominates the temperature rise of the liquid aluminum and accelerate its evaporation. During ignition, the heat loss of natural convection significantly affects the ignition performance of aluminum particle, while the heat loss of radiation toward the surrounding air only affects the evaporation rate. Threshold ignition energy of aluminum particle based on numerical calculations is in good agreement with the experiments, which strongly depends on the particle diameter. Ignition delay time depends on the particle diameter and ignition energy. This study will be beneficial to deeply recognize the ignition mechanism of single micron‐sized aluminum particle, especially in the transition region between nanoscale and microscale.     

Mechanism for oxidation of yperite at high temperatures behind shock waves

The model for post-shock oxidation is based on the oxidation kinetics of one of the main intermediate products, chloroethane sulfonic acid. The kinetic constants for decomposition of this substance are calculated based on standard theories. A kinetic scheme for the subsequent reactions is proposed which takes the special conditions behind a shock wave into account (high radical concentrations). A previously developed program is used to calculate the variation in the concentrations of the components during oxidation of chloroethane sulfonic acid in a mixture of methane and air behind a shock wave. The calculations show that useful chemical products can be obtained under these conditions. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 2, pp. 70–74, Mach–April 1999.     

Kinetics and mechanism of thermal decomposition of HMX with metal cupferronate additives

The kinetic features of the thermal decomposition of HMX with metal cupferronate additives, in which the nucleophilic detachment of a proton in HMX by a phenylnitric-oxide anion-radical plays an important role, are established. The logarithms of the rate constants for the decomposition of HMX correlate with the ratio of the charge of the metal cation in the cupferronate to its radius, which indicates a different reactivity of the anion-radical owing to the polarizing effect of the cation. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 52–56, May–June 1999.     

Kinetics of heterogeneous reactions of carbon and oxygen during combustion of porous carbon particles in oxygen

A model of combustion of a high-porosity carbon particle in oxygen is considered, which takes into account heterogeneous and homogeneous chemical reactions inside the particles and radiative heat transfer. The boundaries of the domain where the burning rate depends on the particle temperature are determined. The possibility of two combustion regimes is demonstrated: regime with a high burning rate, where the carbon-oxygen reaction proceeds in a layer adjacent to the particle surface, and regime with a low burning rate, where the reaction proceeds in the entire particle volume. In the regime with a high burning rate, the main product of the reaction between carbon and oxygen is carbon monoxide, whereas both carbon monoxide and carbon dioxide can be formed in the regime with a low burning rate. The kinetic equations of heterogeneous reactions C + O₂ = CO₂ and 2C + O₂ = 2CO are determined, which reveal the retarding effect of carbon monoxide and dioxide on the rates of these reactions. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 11–22, May–June, 2006.     

Ignition of Particles of Wet Woody Biomass under Convective Diffusion of Water Vapor in the Near-Wall Region

This paper presents the results of an experimental and theoretical study of heat and mass transfer during ignition of wet wood particles in a high-temperature gas medium. Experiments were carried out in a setup which provides conditions similar to the combustion spaces of boiler units. The main heat transfer parameters (ambient temperature) and integrated ignition characteristics (ignition delay) were measured. The measurement error of these parameters did not exceed 18%. The convective transfer of water vapor formed during evaporation of pore moisture and pyrolysis products were found to have an insignificant effect on the ignition characteristics and conditions. From the results of the experiments, a mathematical model of the ignition process was developed which describes the simultaneous occurrence of the main processes of thermal preparation under conditions of intense phase (evaporation of water) and thermochemical transformations (thermal decomposition of the organic part of the fuel, thermochemical interaction between water vapor and carbon coke, ignition of volatiles) taking into account the convective diffusion of water vapor and pyrolysis products in the near-wall gas area during the induction period. The theoretical ignition delay is in satisfactory (within the confidence interval) agreement with the experimental value. The numerical model of the diffusion flame adequately (good agreement between experimental and theoretical ignition delays) describes the ignition of a wet wood particle.