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Combustion, Explosion and Shock Waves

2013 year, number 4

Ignition and Combustion of Hydrogen in a Channel with High Supersonic Flow Velocities at the Channel Entrance

V. A. Vinogradov, M. A. Goldfeld, A. V. Starov
Keywords: supersonic velocity, combustor, hydrogen

Abstract >>
Results of experimental investigations of a multi-injector combustion chamber in the attached pipeline regime are presented. An IT-302M hotshot wind tunnel based at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences is used as a source of a high-enthalpy gas (air). The tests are performed at Mach numbers of 3, 4, and 5 in the ranges of the total temperature from 2000 to 3000 K and static pressure from 0.08 to 0.23 MPa. The block of injectors is made in two variants: with different relative lengths of wedge-shaped injectors (cocurrent injection of hydrogen). The influence of the conditions at the combustor entrance on ignition and stable combustion of hydrogen is studied. Intense combustion of hydrogen is obtained only at Mach numbers of 3 and 4. The mechanism of the two-stage evolution of fuel combustion in the combustor is analyzed. The experimental data are analyzed and compared with numerical predictions.

Kinetics of Oxidation and Combustion of Complex Hydrocarbon Propellants: Jet Propellant

A. M. Starik, N. S. Titova, S. A. Torokhov
Keywords: heavy hydrocarbon propellants, jet propellant, reaction mechanism, ignition, cool flame phenomena

Abstract >>
A kinetic model of ignition and combustion of heavy n-alkenes n-C10H 22 and n-C12H26), benzene, and jet propellant Jet-A, hich is modeled by a BD surrogate consisting of n -decane 80%) and benzene (20%), is developed. The model is tested through comparisons with a large set of experimental data on the ignition delay time in both higher-temperature ( T > 1000 K) and low-temperature ( T = 650–950 K) regions and also on the behavior of species concentrations during benzene oxidation in a flow-type reactor and during benzene combustion in a special burner. Other reaction mechanisms developed for the description of combustion of various surrogates modeling kerosene are briefly analyzed. It is demonstrated that the proposed model ensures a more adequate description of the measured ignition delay times than other known kinetic models, especially in the low-temperature range ( T = 650950 K). Specific features of the kinetics of low-temperature oxidation of the BD surrogate are analyzed.

Numerical Simulation of Experiments to Determine Ignition Delays behind Incident Shock Wave

V. Yu. Gidaspov, N. S. Severina
Keywords: shock tube, detonation, ignition delay, numerical simulation, explicit selection of gas-dynamic discontinuities

Abstract >>
This paper presents a physicomathematical model and results of numerical simulation of the initiation and propagation of detonation waves in shock tubes. A combustible mixture of hydrogen and oxygen diluted with argon is considered. A detailed structure of the flow in the shock tube is obtained by calculations. The calculated ignition delay was compared with experimental data.

Numerical Study of Detonation Waves in a MonofuelGas Mixture in Sharply Expanding Pipes

A. G. Kutushev, V. F. Burnashev, U. A. Nazarov
Keywords: combustion, detonation, shock wave, detonation wave, particle combustion front, monofuel, pipeline, mass content of particles

Abstract >>
Mathematical simulation of the propagation mechanisms of combustion waves and heterogeneous detonation in sharply expanding pipes was performed using the equations of two-dimensional axisymmetric unsteady motion of a reacting mixture of a gas and monofuel particles. The influence of the main determining parameters of the gasparticle mixture and the pipeline on the propagation of nonstationary detonation waves was studied. Dependences of the critical ratio of the pipe diameters of the composite pipeline on the relative mass content of monofuel particles of different sizes are given.

Characteristics of Combustion and Detonation of MethaneCoal Mixtures

A. A. Vasil'ev
Keywords: combustion, detonation, critical ignition energy, critical energy of detonation initiation, explosion hazard, environmental research

Abstract >>
Calculated and experimental data on combustion and detonation in mixtures where oxygen or air is used as an oxidizer and methane or coal dust is used as a fuel are presented.

Continuous Spin Detonation of Synthesis GasAir Mixtures

F. A. Bykovskii, S. A. Zhdan, E. F. Vedernikov
Keywords: continuous spin detonation, synthesis gas, air, transverse detonation wave, combustor, fuel injection system

Abstract >>
Regimes of continuous detonation burning of synthesis gas–air mixtures in transverse (spinning) detonation waves are obtained for the first time in an annular cylindrical flow-type combustor. Carbon oxidehydrogen mixtures with volume proportions of [CO]/[H2] = 1/1, 1/2, and 1/3 are studied in a wide range of fuel-to-air equivalence ratios. The maximum detonation wave velocity equal to 1.57 km/s is observed for the mixture of CO + 3H2 + air with a moderate (about 15%) excess of the fuel. The limits of existence of continuous detonation in terms of the equivalence ratio and the minimum specific flow rate of the mixture are determined. The range of detonation regimes obtained is constructed in the coordinates of the equivalence ratiospecific flow rate of the mixture.

Complex Modeling of Melting of an Aluminum Nanoparticle

A. V. Fedorov, A. V. Shulgin
Keywords: molecular dynamics, nanoparticles, melting, specific heat

Abstract >>
A semi-empirical model of molecular dynamics is proposed within the molecular dynamics approach. The model is verified against the experimental dependence of the melting temperature of aluminum nanoparticles on their size. The specific heat of the particle and the phase transition heat are determined as functions of the initial size and temperature of the particle. It is demonstrated that these dependences tend to the limiting dependences, which describe the particle size in the volume phase, as the particle size increases. A comparison of the aluminum nanoparticle melting characteristics alculated by the model of molecular dynamics and by the phenomenological model reveals reasonable agreement in terms of the melting time.

Fireball and Shock Wave Dynamics in the Detonation of Aluminized Novel Munitions

J. M. Gordon, K. C. Gross, G. P. Perram
Keywords: shock waves, fireball, classification, detonation, aluminized RDX, SedovTaylor point blast model

Abstract >>
High-speed 4-kHz visible imagery from 13 field detonations of aluminized RDX munitions with varying liner compositions are collected to study shock wave and fireball dynamics. The Sedov–Taylor point blast model is fitted to shock front temporal history data, and blast wave characteristics are interpreted by varying the energy release factor s and blast dimensionality n . Assuming a constant rate of energy release (s=1), the SedovTaylor model establishes a near-spherical expansion with the dimension n=2.23.1 and shock energies of 0.58.9 MJ. These shock energies correspond to efficiencies of 215% of the RDX heats of detonation. A drag model for the fireball size yields a maximum radius of ≈5 m, which is consistent with the luminous fireball size in visible imagery, and initial shock speeds corresponding to Mach numbers of 4.78.2. Initial shock speeds are smaller than the RDX theoretical maximum speed by a factor of 34. Shock energy decreases if aluminum is in the liner rather than in the high explosive.

Adiabatic Thermal Explosion in Disperse Condensed Systems with Limited Solubility of the Reactants in the Product Layer

V. Yu. Filimonov, K. B. Koshelev
Keywords: thermal explosion, homogeneity zone, kinetic regime, activation energy, scale of heterogeneity

Abstract >>
A mathematical model of the self-heating of dispersed solid mixtures is considered taking into account the boundary kinetics of formation of the intermediate product phase. It is shown that decreasing the ratio of the characteristic diffusion time to the characteristic reaction time can lead to a transition from the diffusion regime to the kinetic regime, resulting in a change in the effective activation energy of the synthesis and the growth pattern of the product layer. This change may be due to decreases in the heterogeneity scale of the mixture and the ratio of the activation energy of the formation of the new phase to the activation energy of diffusion. An analytical model of the solid-state reaction in the kinetic regime was developed and used to obtain temperature dependences of the coordinates and velocities of the boundaries of the growing layer.

Reasons for the Anomalous Dependence of the Specific Impulse of Rocket Propellants on the Content of Borohydride

D. B. Lempert, E. M. Dorofeenko
Keywords: specific impulse, high-energy compositions rocket propellant, boron-containing fuel

Abstract >>
We investigate the cause of the appearance of two maxima in the curve of the specific impulse of a high-energy composition with increasing content of the borohydride component in it. It is shown that such anomalies can occur for some values of the enthalpy of formation of the oxidizer, for a certain hydrogen content in the boron-containing fuel, etc. As the content of borohydride in the composition is increased, a time comes when oxygen is not sufficient for the formation of B2O3 and excess boron begins to be oxidized by nitrogen to condensed boron nitride. Under certain conditions, this can lead to a second local maximum of the specific impulse.

Effect of Diethylenetriamine on the Structure of Detonation Waves in Nitromethane

A. V. Utkin, V. M. Mochalova, A. A. Logvinenko
Keywords: detonation, chemical spike, chemical reaction zone, nitromethane, nitromethane/diethylenetriamine mixture

Abstract >>
This paper presents the results of experimental studies of the reaction zone structure in steady-state detonation of nitromethane sensitized by diethylenetriamine (DETA). The concentration of DETA was varied within 0.012515%. It is shown that small additions of DETA lead to a qualitative change in the flow pattern in the reaction zone. After the shock, the mass flow rate continues to increase for about 10 ns, reaches a maximum, and only then decreases. The amplitude of the chemical spike decreases by an order of magnitude. These features are explained by the decomposition of nitromethane sensitized by DETA in front of the shock wave, which is due to a sharp increase in the initial reaction rate.

Equations of State of Silver Azide and Calculation of Its Hugoniots

A. M. Molodets, Yu. N. Zhuravlev
Keywords: silver azide, shock compression, equation of state, dynamics of crystal lattice, ab initio calculations

Abstract >>
The thermal and caloric equation of state of the orthorhombic phase of silver azide are presented. For this material, pressuretemperature relations along the Hugoniots of the material with different porosity and shock velocityparticle velocity relations are calculated. The calculations are performed for pressures up to 3 GPa and temperatures of 300500 K, particle velocities of up to 0.4 km/s, and initial porosity of 11.5. The relative positions of the Hugoniots and equilibrium lines of polymorphic transformations of silver azide in the indicated region of thermodynamic variables is discussed.

Limiting Shock Compression of Metals of Ultra-Close Packing

S. S. Batsanov
Keywords: shock waves, compression, structure, conversions, cations

Abstract >>
Based on the conservation law and the Hugoniot equation, a simple relation is derived for the limiting compression of metals whose volume corresponds to the extremely close packing of cations. It is predicted that the metals under extreme compression by shock waves will have low electronic conductivity up to the level of semiconductors. In the case of polyvalent metals, their further compression will lead to electronic transitions with increased charge of cations.

Interaction of a Shaped-Charge Jet with Moving Reactive Armor Plates

I. F. Kobylkin, N. S. Dorokhov
Keywords: shaped-charge jet, reactive armor, continuous and discrete interactions, wearing and deflection of jet, transverse wavelike perturbations of the jet

Abstract >>
The mechanisms of the stationary and nonstationary interaction between a metal shaped charge jet and the front reactive armor plate (moving toward the jet) and rear (moving behind the jet) reactive armor plate. The range of interaction parameters in which these mechanisms take place was determined. The interaction of the shaped-charge jet with the front plate is mainly stationary and leads to the wearing of the jet in the transverse direction (reduction in the diameter of the jet) and its deflection by a small angle. The interaction of the shaped-charge jet with the rear plate is mainly of a nonstationary discrete nature and forms unilateral transverse perturbations in the jet, which, developing, lead to its bending and subsequent destruction.

Optimization of the Initiation Capability of a Microdetonator

Ai-jun , Nan Yan, Wan-jun Geng, Tao Chen, Jun-feng Ma
Keywords: microdetonator, manganin gauge, output pressure, initiation

Abstract >>
The initiation capability of a microdetonator 0.9 mm in diameter and 3 mm in height is studied. The critical height of the lead azide explosive is 1.8 mm. The optimal ratio of the heights of the primary and secondary explosives in a microdetonator is determined to be 0.72.3. At an identical ratio of the primary and secondary explosive heights, the output pressure changes from the highest to the lowest value in the sequence from CL-20 to HMX and then to RDX.