Gas detonation in a channel with transverse ribs

Results of experiments on detonation propagation in a rectangular horizontal channel with high ribs on the lower wall are presented. The experiments were performed with acetylene-oxygen mixtures. An interval of initial pressures is found, in which low-velocity detonation with a steady velocity of 0.38–0.55 of the Chapman-Jouguet velocity without losses exists. This detonation wave is a system consisting of a shock wave and a flame. Owing to gas outflow to the layer occupied by the ribs, the flame is maintained at a constant distance from the shock wave, which is approximately equal to the free transverse size of the channel. This distance weakly decreases with increasing initial pressure and is almost independent of the burning rate of the gas at standard temperature. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 82–86, September–October, 2007.     

Characteristic regimes of multifront-detonation propagation along a convex surface

Experimental results of multifront-detonation diffraction on a convex curvilinear surface are given. An estimate of the minimum gas-layer thickness, which is necessary for the external circumferential rotation of a multifront wave, is proposed. The characteristic propagation regimes are established in annular channels: complete destruction of detonation and combustion, high-speed combustion, galloping detonation, and multifront detonation. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 86–92, September–October 1999.     

Heat fluxes to combustor walls during continuous spin detonation of fuel-air mixtures

Pioneering measurements of heat fluxes to the walls of flow-type combustors of different geometries were performed in regimes of continuous spin detonation of fuel-air mixtures under unsteady heating. These heat fluxes are compared with those observed in the regime of conventional turbulent combustion in the same combustor. Air is used as an oxidizer, and acetylene or hydrogen is used as a fuel. For identical flow rates of the fuel, the heat fluxes to the combustor walls in regimes of continuous spin detonation and conventional combustion are close to each other; their mean steady values are ≈1 MW/m² (≈0.5% of the enthalpy flux of the products over the channel cross section). In both detonation and combustion regimes, the maximum heat fluxes penetrate into the walls in the mixing region (where the heat release occurs). In the case of detonation, regenerative cooling of the combustor walls by the flow of the fresh mixture occurs in the heat-release region (region of propagation of the detonation-wave front). The regeneration becomes less effective in the downstream direction because of the shorter time of contact between the walls and the cold mixture and a longer time of contact between the walls and the hot products. More intense heating persists downstream of the front, where the regeneration ceases, but the temperature of the products is high. The character of heating of the wall in the region of rotation of the front of spin detonation waves depends on the number of these waves: the zone of the maximum heat release becomes narrower with increasing number of waves. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 1, pp. 80–88, January–February, 2009.     

Detonation of a coal-air mixture with addition of hydrogen in plane-radial vortex chambers

Results of an experimental study of continuous and pulsed detonation of a coal-air mixture with addition of hydrogen in plane-radial vortex chambers 204 and 500 mm in diameter are presented. The tested substance is pulverized activated charcoal. A method of coal powder supply through narrow channels by means of adding the gas at the injector entrance is found. Stable regimes of continuous spin detonation with one or two transverse detonation waves moving with velocities of 1.8–1.6 km/sec are obtained for the first time in the combustor 204 mm in diameter. The frequency of pulsed detonation with radial waves is 4–4.8 kHz. The limits of continuous detonation in the combustor 500 mm in diameter are extended: regimes of continuous spin detonation with a large number (5–8) of transverse waves moving with velocities of 1.8–1.5 km/sec are obtained, the amount of hydrogen added to coal is reduced to 2.8%, and combustion of coarser fuel particles is ensured owing to an increased residence time of the mixture in the combustor. The wave structure and the flow in the vicinity of the waves are reconstructed in the combustor plane.     

Initiation and development of detonation as a result of the action of weak shock waves on liquid explosives

Summary Clearly, in handling liquid explosives safely it is important to take into account, among other things, their actual physical state. Whereas for most liquid explosives the initiating pressures for simple homogeneous compression are high (60–120 kbar); in the presence of cavitation the same liquids exploded at relatively low pressures (about 0.1–10 kbar) and, in their sensitivity to waves shock, resemble (or may even be inferior to) powdered explosives (according to [16] the initiating pressure for PETN at a density of 1.0 g/cm³ is 2.5 kbar). Under favorable conditions, especially if the vessel is capable of conducting elastic disturbances, the development of explosion in liquids leads to a low-velocity detonation which may subsequently resolve into normal detonation. In this respect, the propagation of low-velocity regimes in liquids is very similar to the propagation of low-velocity detonation in powdered explosives. Our present lack of definite ideas, about the specific reaction initiation mechanism associated with the collapse of cavities in liquids places considerable diffculties in the way of any quantitative analysis of the experimental data on the excitation and propagation of explosions. Fizika Goreniya i Vzryva, Vol. 5, No. 3, pp. 354–361, 1969     

Special features of combustion of propane-air and hydrogen-air mixtures in a narrow tube

The special features of combustion-wave propagation in a narrow tube have been studied experimentally in low-velocity regimes for propane-air and hydrogen-air mixtures. For propane mixtures, the increase in the curvature of the flame surface correlates with the displacement of the maximum into the region of enriched mixtures in the dependence of the combustion velocity on the mixture composition. Combustion of lean hydrogen-air mixtures is accompanied by acoustic oscillations which lead to a narrowing of the range of flame, existence relative to the combustible-gas flow rate. For enriched mixtures, the flames are stable, and they exist at a hydrogen concentration close to the value for the upper concentration limit of flame propagation. Institute of Chemical Kinetics and Combustion, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 6, pp. 14–21, November–December, 1997     

Formation of carbon clusters in deflagration and detonation waves in gas mixtures

Numerical and experimental results of studying the formation of carbon clusters due to propagation of deflagration and detonation waves in enriched acetylene-oxygen and acetylene-air mixtures are described. Experiments are performed in tubes of different diameters (including tubes filled by a porous medium) with wide-range variations of the initial pressure and the fuel-to-oxidizer ratio. A large variety of carbon clusters formed in different regimes of burning of the mixture is found. A typical size of condensed carbon particles is 15–100 nm. In the case of detonation in a porous medium, the size of carbon particles is 15–45 nm; in some tests, large individual fullerene-type particles 150, 400, and 950 nm in size are formed. The fraction of condensed carbon in the total amount of carbon in the initial mixture is found to depend on the wave type; detonation is characterized by the minimum “yield” of condensed carbon. The amount of condensed carbon increases with increasing acetylene concentration in the mixture and initial pressure. The size of carbon particles in the case of deflagration is greater than that in the case of detonation. Cooling of reaction products decelerates condensation and interrupts the growth of carbon particles. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 81–94, May–June, 2008.     

Two-dimensional numerical simulation of deflagration-to-detonation transition for a porous explosive using a model of a multivelocity heterogeneous medium

The model of a multivelocity heterogeneous medium is used for one- and two-dimensional numerical calculations of the deflagration-to-detonation transition for charges of a porous explosive enclosed in a casing. Calculation results are compared with experimental data. Depending on the charge diameter, different explosion regimes — detonation and low-velocity explosive transformation — are registered in both the two-dimensional calculations and experiments. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 97–106, May–June, 2000.     

Physical model of low-velocity detonation in plasticized HMX

A physical model of low-velocity detonation in plasticized HMX is considered. In this model, a low-velocity detonation wave is a combination of a weak leading shock wave and a subsequent compression wave. This combination is formed by the simultaneous effects of energy release and spreading of the reacting medium. The main features of low-velocity detonation observed in experiments are reproduced in two-dimensional calculations. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 102–112, January–February, 2008.     

Propagation of plane supercompressed detonation waves in gases

An approximate mathematical model has been constructed for the propagation of plane supercompressed detonation waves in gases. An exact analytical solution of the Riemann wave type has been obtained and so have approximate analytical solutions that describe the excitation and attenuation of supercompressed waves when detonation is initiated in the galloping mode. M. A. Lavrent'ev Institute of Hydrodynamics, Novosibirsk, 630090. Translated from Fizika Goreniya i Vzyrva, Vol. 31, No. 5, pp. 101–113, September–October, 1995.     

Effect of chemically inert particles on parameters and suppression of detonation in gases

An algorithm for calculating the parameters of a steady one-dimensional detonation wave in mixtures of a gas with chemically inert particles and estimating the detonation-cell size in such mixtures is proposed. The calculated detonation parameters and cell size in stoichiometric hydrogen-oxygen mixtures with W, Al₂O₃, and SiO₂ particles are used to analyze the method of suppression of multifront gas detonation by injecting chemically inert particles ahead of the leading wave front. The ratio between the channel diameter and the detonation-cell size is used to estimate the limit of heterogeneous detonation in the mixtures considered. The minimum mass of particles and the characteristic cloud size necessary for detonation suppression are calculated. The effect of thermodynamic parameters of particles on the detonation suppression process is analyzed for the first time. Particles with a high specific heat and (if melting occurs) a high phase-transition heat are found to exert the most pronounced effect. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 77–88, May–June, 2009.     

Gap effect on the initiation of detonation in gas mixtures in cylindrical combustion chambers. II. Triggering of detonation within a turbulent flame

Schlieren moving-picture photography is used to study the burnup of oxygen gaseous mixtures in a cylindrical chamber with a gap at its periphery. It is found that a flame penetrating from the chamber into the gap can accelerate up to detonation speeds. The reaction wave in the gap precedes the primary combustion front propagating through the chamber and the reaction products escaping the gap create secondary combustion sources in the chamber. A process occurs in which a detonation wave that appears in the gap near one flank of the flame enters the main volume through the opposite flank, first triggering an explosion in the turbulent combustion zone (“an explosion within an explosion”) and then a detonation wave in the unreacted gas charge (“knock” in an engine). An interpretation is provided for the gas-dynamic structure of the secondary combustion source which is created in the cylindrical combustion chamber by a detonation wave propagating in the gap. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 4, pp. 77–87, July–August 1998     

Nonclassical regimes of wave diffraction in combustible mixtures

Experimental and numerical results of investigating the diffraction of combustion and detonation waves, including the diffraction in unsteady deflagration-to-detonation transition regimes, are presented. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 137–143, November–December, 2006.     

Structure of detonation waves in tetranitromethane and its mixtures with methanol

A VISAR laser interferometer was used to measure mass velocity profiles in steady-state detonation waves in tetranitromethane and its mixtures with methanol. In the experiments with tetranitromethane, the chemical-spike pressure was found to be 1.7 times higher than the Chapman-Jouguet pressure. In mixtures with nearly stoichiometric methanol concentrations, the detonation front remained stable, but the chemical-spike amplitude increased suddenly and the shock broadened, probably due to the decomposition of the explosive at the front. A 50% increase in methanol concentration led to instability of the detonation front manifested in oscillations in the mass velocity profiles. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 95–100, May–June, 2009.     

Effect of a nanosecond gas discharge on deflagration to detonation transition

The possibility of using a high-voltage nanosecond discharge to initiate gaseous detonation was shown experimentally. The experiments were performed with C₃H₈ + 5O₂ and C₃H₈/C₄H₁₀ + 5O₂ + xN₂ (x = 0–10) mixtures at an initial pressure of 0.15–0.6 atm. The discharge was initiated by a voltage pulse of duration ≈60 nsec and amplitude 4–70 kV; the energy input was 0.07–12 J. Under the conditions of the experiment, three flame propagation regimes were observed: slow combustion, transient detonation, and Chapman—Jouguet detonation. For the initiation of the C₃H₈+ 5O₂ mixture in a tube of diameter 140 mm, the length of the deflagration to detonation transition was 130 mm at an initial pressure of 0.3 atm and an initiation energy of 70 mJ. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 80–90, March–April, 2006.     

Flame propagation in mixtures of monogermane and oxygen. II. Peculiarities of flame propagation and the structure of combustion waves

Different flame propagation regimes, including a two-wave regime, are studied in a closed pipe with single ignition of GeH₄−O₂ mixtures. It is shown that, depending on the initial conditions and, in particular, on the composition of the initial mixtures, spatially separated chemical reaction waves for oxidation and decomposition of monogermane are observed in certain parts of the reaction vessel which lead to the formation of a two-layer deposit of GeO/Ge. The temporal sequence of the separated combustion wave and wave from which layers of solid products are deposited, as well as the location of the deposition zones in the reaction vessel, are determined by two interacting chain processes—the oxidation and decomposition of monogermane. The thermal relaxation kinetics of the reactive mixture after passage of the combustion waves is determined by the rate of conductive heat transfer from heated solid particles (reaction products) to the gaseous phase. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 77–84, January–February 1999.     

Flame propagation in hydrogen-air mixtures in a tube

The propagation of a hydrogen-air flame in a closed tube 76 mm in diameter and 2500 mm in length with and without a water film moving along the tube walls was studied experimentally and theoretically, it has been found that in a smooth-wall tube the maximum turbulization factor ranges between 10 and 30 for mixtures with the volume concentrations of hydrogen 15–30%. The presence of a moving water film on the tube walls intensifies the combustion process, which manifests itself in the essential acceleration of the detonation pressure rise. However, at the same time, the maximum explosion pressure for near-stoichiometric mixtures increases, while that for leaner compositions decreases. The results obtained are interpreted qualitatively. Balashikha. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 6, pp. 14–19, November–December, 1993.     

Detonation of a thin explosive layer in evacuated tubes

Detenation of thin layers of dispersed primary and secondary high explosives (HE) on the outer surface of glass and plastic tubes 0.6–3 mm in diameter was examined at an initial air pressure inside the tube of 0.1 MPa to 30 Pa. It is shown that, under these conditions, the air practically does not influence the detonation velocity, which for secondary explosives (PETN, RDX, and HMX), is lower than or approximately equal to the Chapman-Jouguet detonation velocityD _CJ for a homogeneous mixture of the same substances. Experiments with a primary HE (lead azide) revealed regimes with a wave velocity higher thanD _CJ and a varying reaction zone pattern. When tubes containing a layer of a secondary HE were filled with an explosive gas mixture, waves of a hybrid detonation with a velocity both higher and lower than that in the evacuated tubes was observed. In tubes with diameter 2–3 mm, detonation proceeded in a spinning regime over the entire range of the initial pressure and at a velocity higher thanD _CJ. It is concluded that in the evacuated tubes with a thin HE layer on the walls, ignition is transferred by the stream of hot detonation products moving at the head of the detonation wave. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 56–67, November–December 1998     

Continuous detonation in the regime of self-oscillatory ejection of the oxidizer. 1. Oxygen as a oxidizer

Results of an experimental study of continuous spin and pulsed detonation of hydrogen-oxygen and acetylene-oxygen mixtures in a flow-type annular combustor 10 cm in diameter with channel expansion in the regime of oxidizer ejection are presented. Through comparisons with the mechanical analogy of a piston-driven pump, it is found that the detonation wave serves as a pump for the oxidizer, and the rarefaction wave serves as a suction piston. Stable regimes of continuous spin detonation with one transverse wave are observed under the test conditions used; the wave velocity is D = 1.76–1.6 km/sec for hydrogen and D = 1.46–1.2 km/sec for acetylene. The frequency of the pulsed detonation wave is 7.3-5 kHz in the H₂-O₂ mixture and approximately 2.5 kHz in the C₂H₂-O₂ mixture.     

Control of the deflagration-to-detonation transition in systems with resistance

This paper develops an approach to controlling gas combustion, including deflagration-to-detonation transition, based on using systems with resistance, such as porous media, periodic obstacles, rough tubes, etc. Gas combustion in these systems involves various physicochemical interactions: interfacial heat transfer, including combustion failure, flame quenching in fast pulsations (jets), transition to turbulence, generation of pressure waves in the flame zone, formation of hotspots, etc. These interactions result in a number of steady-state regimes with a uniform velocity of propagation of thermal waves — low-, high-, and sonic-velocity regimes, low-velocity detonation, and normal detonation with heat and momentum losses. Systems with porous media and periodic obstacles are considered as examples of systems with resistance. It is shown that with the effects of Lewis numbers taken into account, the steady-state velocities in the high-velocity regime for CH₄/Air, C₃H₈/air, and H₂/air systems over wide parameter ranges can be represented by a single relation Re = 6 · 10⁻⁴Pe³ in the coordinates (Re-Pe) for systems with porous media. Steady-state velocities in the sonic velocity regime for C₃H₈/air and H₂/air systems are described in the same coordinates by a single function Re = 120Pe^4/3 for systems with porous media and periodic obstacles. A condition for pressure generation in the flame zone at sonic velocities was obtained analytically. Problems involved in the implementation of the approach of controlling high-velocity combustion processes in systems with resistance are discussed.