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     

Experimental investigation of detonation of nitric acid solutions

Detonation of mixtures of concentrated (94–100%) nitric acid with nitromethane, diethylene glycol dinitrate, nitroglycol, trinitrotoluene, dinitrotoluene, acetic anhydride, and dichlorethane was studied experimentally. The detonation failure diameter was measured in glass tubes. For mixtures of nitric acid with nitromethane, dinitrotoluene, and trinitrotoluene, its minimum values are smaller than 1 mm and correspond to zero oxygen balance of the mixtures (A=0). Nitroglycol (A=0) and its mixtures containing less than 20% nitrogen acid have the same detonation diameter (2 mm), which is larger than that for a mixture of nitric acid with diethylene glycol dinitrate (1 mm forA=0). The minimum values of the detonation diameter for mixtures of nitric acid with acetic anhydride and dichlorethane (2 and 3 mm) are shifted towardA<0. Comparison of the detonation diameter with calculated values of the heat of explosion and analysis of the experimental results within the framework of Dremin’s theory of the detonation failure diameter show that nitric acid enhances the reactivity of nitrocompounds in a shock wave more considerably than the reactivity of nitroesters. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 84–92, January–February, 1988.     

Specific Features of Synthesis of Detonation Nanodiamonds

It is demonstrated that the Chapman-Jouguet parameters for high explosives used in nanodiamond synthesis are located in the region of liquid nanocarbon; therefore, the chemical reaction zone of the detonation wave involves formation of carbon nanodroplets, which are later crystallized into nanodiamonds on the segment of the isentrope of expansion of detonation products, passing through the region of stability of nanodiamonds in the pressure range of 16.5–10 GPa and the temperature range of 3400–2900 K. Soot in the resultant mixture is the product of amorphization of nanodroplets rather than graphitization of ultrafine diamonds. The influence of detonation conditions of high-explosive charges in an explosive chamber on nanodiamond synthesis is analyzed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 104–116, September–October, 2005.     

Numerical simulation of shock-wave initiation of heterogeneous detonation in aerosuspensions of aluminum particles

Numerical simulations of flows of reacting two-phase media in a two-velocity, twotemperature approximation are used to study the shock-wave initiation of detonation in aerosuspensions of aluminum particles in oxygen. The conditions in a high pressure chamber under which detonation can develop after rupture of a diaphragm are determined. Two initiation scenarios are established that depend on the localization of the initiation source. It is shown that initiation brings on a self-sustained detonation regime (Chapman-Jouguet or incompletely compressed, depending on the relaxation parameters). The required initiation energy is estimated and ignition criteria are formulated. The possibility of detonation initiation when insufficiently strong shock waves are reflected from a rigid wall is discussed. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 81–88, May–June 1999.     

Solid-state detonation velocity limits

The ranges of solid-state detonation velocities are estimated, based on the volume velocity of sound in the reacting mixture (lower limit) and the wave velocity corresponding to the pressure of polymorphic transformation of the product with formation of a more dense phase (upper limit). The latter values are consistent with gas-dynamic estimates of detonation velocities and correlate with detonation velocities of typical high explosives. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 104–106, September–October, 2007.     

Density distribution at the detonation front of cylindrical charges of small diameter

A synchrotron radiation based technique is use to study the density distribution at the detonation front and its neighborhood for condensed explosives. Particular data are obtained on the structure of the detonation front in TNT, RDX, and an alloy of TNT with RDX; a comparison of the data with those obtained using different techniques confirms the correctness of the technique. It is concluded that adequate information on the structure of the chemical-reaction zone can be obtained for charges of small diameter. At the same time, it is shown that the Chapman-Jouguet parameters for such charges are far from their predicted values for an infinite medium. The results of the work, including those on the curvature of the detonation front in charges of small diameter, supplement the existing knowledge of the detonation transformation in condensed explosives. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 91–99, March–April, 2007.     

Critical diameter for and fluctuations in detonation of solutions of dinitrotoluene in nitroglycol

The critical detonation diameters of nitroglycol and solutions of dinitrotoluene in nitroglycol in paper shells are measured. The frequency of the detonation fluctuations is determined. Data with glass and paper shells are the same. The frequency of the fluctuations is independent of the concentration of the solution at ≈7 MHz. The detonation parameters of these solutions are compared with systems which detonate in a low-frequency (≈2 MHz) spin regime. When the dinitrotoluene content of the solution is ≤15%, the critical detonation diameter is constant and equal to that for nitroglycol, but as the dinitrotoluene concentration is raised, the critical detonation diameter increases. The experimental results are in good agreement with theory. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 97–102, May–June 1999.     

Initiation of detonation in flows of fuel-air mixtures

Regimes of self-ignition of the fuel mixture obtained by controlled separate injection of hydrogen and air into a plane-radial vortex chamber with a rapid (0.2 msec) transition to detonation have been realized for the first time. Self-ignition occurs in the stoichiometric region with a slightly higher (up to 6–30%) content of hydrogen and, normally, in a subsonic flow. The energy of guaranteed detonation initiation is determined for combustors of different geometries and different ratios of fuel components by using a thermal pulse produced by blasting a wire by electric current. Detonation initiation is ensured by using energy of 0.1 J. It is found that the main contribution of energy into the flow of the mixture occurs at the stage of evaporation (ionization) of copper of the blasted wire. The continuous spin detonation regime is found to decay as the exit cross section of the combustor is reduced. In the regime of combustion, both detonation and conventional turbulent combustion, the pressure at the periphery of the plane-radial vortex chamber is lower and the pressure at the edge of the exit orifice is higher than that in the case of exhaustion of cold fuel components. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 110–120, May–June, 2007.     

Diffraction estimate of the critical energy for initiation of gaseous detonation

A criterion for the excitation of detonation is proposed: the critical initiation energy equals the work performed by the expanding detonation products along a path length equal to the longitudinal dimension of a cell. The initial radius of the layer is chosen to be equal to the radius of the detonation wave diffracted at 90° edge at the time the axial rarefaction wave converges on the axis of the gaseous charge. Formulas are obtained for estimating the critical energy for initiation of plane, cylindrical, and spherical detonation waves. The calculated values are in good agreement with experiment. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 4, pp. 72–76, July–August, 1998.     

Detonation waves in interstellar gas

In astronomy there is a large amount of observational data on the phenomenon of sequential star formation from a single molecular cloud. In this process, a cluster of stars of the same generation creates favorable conditions for the formation of stars of the next generation. A star-forming wave whose velocity is estimated to be10–30 km/sec travels over a molecular cloud of interstellar gas. In the present paper, the self-sustained star-formation phenomenon is claimed to have all features of a detonation process and the star-forming wave is treated as a detonation one. The velocities of the detonation and star-forming waves are estimated to be (∼27 km/sec) and (∼13 km/sec), respectively. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 88–93, January–February, 1997     

Protection of an explosion chamber against fracture by a detonation wave

The results of numerical simulation of the protective properties of layered and porous shields that are used to reduce peak stresses and to prevent failure of the walls of an explosion chamber under detonation loading are presented. It is shown that porous shields have stronger protective properties than layered shields of the same thickness. Institute of Applied Mathematics and Mechanics, Tomsk 634050. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 131–137, January–February, 1997.     

Detonation combustion of coal

Results of an experimental study of continuous spin detonation of a coal-air mixture with addition of a certain amount of hydrogen in a plane-radial vortex chamber 500 mm in diameter are presented. The tested substance is fine-grained cannel coal from Kuzbass, which has a particle size of 1–7 μm and contains 24.7% of volatiles, 14.2% of ashes, and 5.1% of moisture. Stable regimes of continuous spin detonation with transverse detonation waves having velocities of 1.86–1.1 km/s with respect to the cylindrical wall of the combustor are obtained for the first time. The mass fraction of hydrogen is 1.5–0.88% of the air flow rate and 50–3.4% of the coal consumption rate. The maximum specific coal consumption rate of 106 kg/(s · m²) is obtained.     

Measurement and calculation of the ideal detonation velocity for liquid nitrocompounds

Results of experimental measurements are presented for the dependence of the detonation velocity on the charge diameter for homogeneous nitromethane and propylene glycol dinitrate and for the ideal detonation velocities for allyl nitrate, diethlyene glycol dinitrate, methylene glycol dinitrate, and ethyl nitrate. Literature data on measurement of the dependence of the detonation velocity on the charge diameter for liquid TNT, nitroglycerin, glycol dinitrate, and methyl nitrate are collected. It is shown that measured values of the ideal detonation velocity are in good agreement with calculated values obtained by the SD method, which uses the equation of state of materials at a high pressure (see B. N. Kondrikov and A. I. Sumin, Fiz. Goreniya Vzryva, No. 1, 1987). A correlation between the ratio of the critical detonation velocity to the ideal velocity and the heat of explosion is obtained, which makes it possible to estimate the limiting value of the latter at which homogeneous liquid nitrocompounds lose detonatability. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 5, pp. 111–117, September–October 1998.     

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     

Detonation combustion of gas mixtures using a hypervelocity projectile

This paper considers, from a unified point of view, problems of initiation of detonation combustion of a gaseous mixture using a hypervelocity projectile (HVP), The consideration is based on the energy criterion forHVP-induced detonation initiation. Experimental results are given that support the correctness of the criterion in a wide range of diameters (5–250 mm),HVP velocities (800–3500m/sec), and compositions of explosive mixtures (from active fuel-oxygen to hard-to-detonate fuel-air mixtures). The processes ofHVP interaction with an explosive mixture are classified. The previously unknown effect of jet formation of a detonation wave from a ballistic wave (at velocities less than the detonation velocities) was discovered for anHVP with a plane bow. Lavrentśev Institute of Hydrodynamics, Siberian Division, of the Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 5, pp. 85–102, September–October, 1997.     

Limits of gaseous detonation spraying

The maximum possible values of adhesion and cohesion are calculated for a number of powder materials, substrate materials, sizes of installation barrels, and compositions of explosive gas mixtures. These data give a clear idea about the areas of applicability of gaseous detonation spraying. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 113–116, September–October, 2006.     

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.     

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.     

Detonation of pressed HMX charges

The pressure-profile measurement results obtained in the shock-wave front in bromoform upon detonation of HMX charges of diameter 40 mm and length 22–110 mm are reported. The initial density of the charges was 1.81 g/cm³. In all the experiments, a monotonic decrease in pressure occurred, and a chemical peak was not observed. With increase in the charge length, the maximum pressure values first increase and then decrease. An analysis of the pressure measurement results shows that, for the given charge size and the initiation system used, the process of HMX detonation occurs in a nonstationary regime. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 83–86, July–August, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 97-03-32000).     

Reactive impulse from the explosion of a gas mixture in a semiinfinite space

The reactive impulse from the explosion of an acetylene-oxygen mixture in a cylindrical chamber is calculated and measured. The gas mixture was charged into the closed end of the chamber and filled all or part of the length of the chamber. In the latter case, air filled the remaining part of the chamber volume. With a variation in the ratio of chamber and charge lengths from 1 to 7–10, the specific impulse from detonation of the mixture increases from 160 to 500–540 sec. In the case of fuel-air mixtures, the theoretical specific impulse is several times lower per unit mass of the mixture and several times greater per unit mass of the fuel. Lavrent'ev Institute of Hydrodynamics. Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizikia Goreniya i Vzryva. Vol. 30, No. 5, pp. 90–97, September–October, 1994.