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Combustion, Explosion and Shock Waves

2012 year, number 6

Effect of Ethanol on the Chemistry of Formation of Precursors of Polyaromatic Hydrocarbons in an Fuel-Rich Ethylene Flame at Atmospheric Pressure

I. E. Gerasimov, D. A. Knyazkov, S. A. Yakimov, T. A. Bolshova, A. G. Shmakov, O. P. Korobeinichev
Keywords: ethylene flame, ethanol, molecular beam mass spectrometry, flame structure, formation of soot precursors

Abstract >>
The effect of the addition of ethanol (EtOH) to the initial combustible mixture on the concentration of various compounds, in particular, those preceding the formation of polyaromatic hydrocarbons in a fuel-rich (equivalence ratio of fuel f = 1.7) flat premixed ethylene/oxygen/argon flame at atmospheric pressure was studied experimentally and by numerical modeling using a detailed mechanism of chemical reactions. Concentrations of various stable and labile species, including reactants, major combustion products, and intermediates in C2H4/O2/Ar and C2H4/EtOH/O2/Ar flames were measured along the height above the burner using molecular beam mass spectrometry. Experimental mole fraction profiles were compared with those calculated using the previously proposed mechanisms of chemical reactions. This mechanism was analyzed to determine the cause of the ethanol effect on the flame concentration of propargyl, the main precursor of polyaromatic hydrocarbons.

Organization of a Pulsed Mode of Combustion in Scramjets

P. K. Tretyakov
Keywords: supersonic flow, combustion, pseudo-shock, pulsed-periodic energetic action

Abstract >>
A new method is proposed to organize the working process in the combustion chamber of a scramjet. The flow velocity in the combustor is maintained close to the velocity of sound. In a constant-area channel, this situation is achieved by organizing combustion in a pulsed wave structure of the pseudo-shock type whose position is determined by parameters of the external thermal-gas-dynamic pulsed-periodic action on the flow. In the channel part with a variable cross section, the mean Mach number close to unity is maintained by choosing an appropriate degree of combustor expansion and appropriate places of fuel injection. The pulsed mode assists in improvement of fuel–air mixing and in reduction of the combustion zone length. The main advantage of this method is the high efficiency of the process determined by the minimum loss of the total pressure and the maximum increase in temperature. Experimental results are given to confirm the possibility of realization of the pulsed combustion mode.

Effects of Recessed Air Jet on Turbulent Compressed Natural Gas Inverse Diffusion Flame Shape and Luminosity

S. Mahesh, D. P. Mishra
Keywords: turbulent inverse diffusion flame, minimum recession, flame luminosity, necking zone

Abstract >>
Effects of the recession of the central air jet on the visible flame height, necking zone, and luminosity of a turbulent compressed natural gas–air inverse diffusion flame in a coaxial burner are investigated in this experimental study. The inner circular tube of the coaxial burner is recessed by 0.25da, 0.5da, and 1.0da, where da is the central tube inner diameter. From the visual observation, the flame height and the necking zone height are observed to decrease exponentially with the air jet Reynolds number with no recession of the central air jet. However, only a marginal reduction in the visible flame height is observed with an increase in the recession height of the air jet as compared to the necking zone height. Interestingly, the necking zone at the flame base disappears beyond the critical recession height of the central jet. Moreover, the recession is found to be effective in eradicating the fuel rich zone and soot ring at the flame base of turbulent compressed natural gas inverse diffusion flame at lower air jet Reynolds numbers.

Theory of Ignition of Metals at Fracture

V. I. Bolobov
Keywords: ignition of fracture fragments, juvenile surface, active sites, adsorption of reactants

Abstract >>
Based on experimental data on the conditions of spontaneous self-ignition of titanium alloys in a mixture of oxygen and nitrogen and water vapor, an equation was derived that relates the critical temperature of ignition of titanium alloys at fracture with partial pressures of oxygen and diluent in the mixture. In the derivation of the equation, it was assumed that the limiting stage of interaction is the dissociative chemical adsorption of the reactants on the active sites of the juvenile metal surface. The calculation results were compared with experimental data on the critical pressure of ignition of titanium alloys performed under various conditions.

Agglomeration of the Condensed Phase of Energetic Condensed Systems Containing Modified Aluminum

E. A. Lebedeva, I. L Tutubalina, V. A. Val'tsifer, V. N. Strel'nikov, S. A. Astaf'eva, I. V. Beketov
Keywords: energetic condensed systems, combustion products, agglomeration, nanoaluminum, protective coating, aluminum carbide

Abstract >>
Thermodynamic analysis of aluminum-containing energetic condensed systems was performed. It was shown that the replacement of aluminum by aluminum carbide led to a decrease in the amount of the condensed phase in the combustion products and a reduction in the specific impulse. The particle size distribution of the condensed phase of samples of energetic condensed systems containing different amounts of aluminum particles coated with aluminum carbide was studied experimentally. It was found that replacing aluminum with a particle size of 18–20 mm nanosized aluminum halved the maximum size of condensed-phase agglomerates of the combustion products.

Effect of Melting on the Critical Ignition Energy of Condensed Explosives by a Short Laser Pulse

A. V. Khaneft, E. V. Duginov
Keywords: melting, ignition criterion, laser pulse, beam radius, PETN

Abstract >>
A criterion for the initiation of explosives with a melting point below the ignition temperature by a short laser pulse is obtained. The criterion obtained is in good agreement with numerical solutions of the heat conduction equation in the cylindrical coordinate system. This criterion made it possible to explain experiments on the initiation of PETN from an open surface by a laser pulse in the range of transparency with variation in the diameter of the light beam. The calculation results coincided with the experiment α = 0.065 cm–1 and the Fresnel reflection coefficient.

Effect of Laser Radiation Absorption Efficiency on the Heating Temperature of Inclusions in Transparent Media

V. G. Kriger, A. V. Kalenskii, A. A. Zvekov, I. Yu. Zykov, B. P. Aduev
Keywords: теория Ми, energetic materials, laser initiation, microhotspot model of thermal explosion, Mie theory

Abstract >>
The efficiency of light absorption by inclusions of various metals in transparent media is calculated using as an example silver azide, lead, and PETN. It is shown that the absorption efficiency, along with the laser pulse energy density, has a decisive influence on the maximum temperature of heating of the inclusion. Dependences of the maximum heating temperature on the radius of the inclusions are plotted for a pulse duration of ~30 ns. Asymptotic expressions are obtained for the dependence of the maximum heating temperature on the pulse duration for an ensemble of inclusions.

Detonation Transmission through High-Modulus Dispersed Media

L. A. Merzhievskii, I. A. Balaganskii, A. D. Matrosov, I. A. Stadnichenko
Keywords: detonation, initiation, porous barrier

Abstract >>
This paper presents the results of experimental studies of detonation transmission through high-modulus powder materials. The features of the process related to the properties of such dispersed media and the prospects for their use in protective devices are discussed.

Numerical Simulation of the Influence of an Axially Asymmetric Charge on the Impact Initiation Capability of a Rod-Like Jet

Y.-D. Li, Y.-S. Dong, Sh.-Sh. Feng
Keywords: axially asymmetric, shaped charge, rod-like jet, impact initiation, numerical simulation

Abstract >>
With the aim to improve the impact initiation capability of a rod-like jet, this paper presents the influence of an axially asymmetric shaped charge on the jet studied by means of numerical simulations. According to Held's initiation criterion, the impact initiation capability of the jet is affected by the jet tip velocity and diameter. The detonation radius over the longitudinal axis, restricted by the charge radius over the same axis, affects the detonation wave in the charge, the force acting on the liner, and, therefore, the jet velocity and shape. Based on these laws, the structure of the axially asymmetric charge is optimized. Compared with axisymmetric jets, axially asymmetric rod-like jets possess a higher impact initiation capability.

Method of Converting a Multimode Penetrator through Point Initiation

W.-B. Li, X.-M. Wang, W.-B. Li, Yu. Zheng
Keywords: point initiation position, explosively formed penetrator (EFP), rod-shaped EFP, detonation wave, numerical simulation

Abstract >>
This study presents the problem of achieving multimode penetrator conversion. By using the same shaped charge and by changing the position of point initiation, the trial demonstrates two types of the penetrator, which are the explosively formed penetrator (EFP) and the rod-shaped EFP. Compared with the EFP, the penetration depth of the rod-shaped EFP is 2.17 times higher, and the penetration aperture only decreases by 31.8%.

Shock-Induced High-Concentration Nitrogen Doping of Titania

P. Chen, X. Gao, J. Liu, Q. Zhou, F. Huang
Keywords: titania, shock doping, nitrogen resources, shock wave, high concentration

Abstract >>
High-concentration nitrogen-doped titania is obtained by detonation-driven flyer impacting on mixtures of TiO2 and different nitrogen precursors. XRD, IR, and XPS spectra are employed to characterize the phase composition, surface absorption, and N-doping concentration of recovered samples. The N-doping concentration is affected by doping nitrogen resources, initial content of doping nitrogen resources, and flyer velocity. A high nitrogen concentration of 13.6 at.% is achieved by shock loading of the mixture of P25 TiO2 and 10 wt.% dicyandiamide (C2N4H4) at 3.37 km/s. A possible shock doping mechanism is discussed.

Initiation of Combustion of a Gas Mixture by an Electric Explosion of an Electrolyte

V. S. Teslenko, A. P. Drozhzhin, P. N. Medvedev, V. I. Manzhalei
Keywords: electric explosion of an electrolyte, discharge in a gas, breakdown in a vapor–gas medium, initiation of combustion

Abstract >>
Initiation of combustion of a stoichiometric propane–oxygen mixture in a bubble located in an electrolyte near a dielectric or metallic wall is performed in experiments. It is demonstrated that combustion in the bubble is initiated by an electric explosion-breakdown of a thin electrolyte layer along the bubble boundary.

Possibility of Nitriding Industrial Ferroalloys in a Nitrogen-Containing Gas Flow

B. Sh. Braverman, Yu. M. Maksimov, Yu. V. Tsybul'nik
Keywords: SHS, ferroalloys, nitriding, combustion limits

Abstract >>
Combustion of ferroalloy powders in a nitrogen-containing gas flow produces nitrogen-containing ligatures in the form of separate unbonded granules at a pressure close to atmospheric pressure.