Noise and vibrations in a combustor with continuous spin detonation combustion of the fuel

Levels of vibrations of the wall of a flow-type detonation chamber of an annular cylindrical geometry in the region of detonation-wave rotation and the noise at a distance of 1 m are measured. In the case of continuous spin detonation of a hydrogen—air mixture, these values are found not to exceed the values inherent in conventional turbulent combustion of the fuel with the same flow rate in the same chamber. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 101–112, September–October, 2006.     

Mathematical model of continuous detonation in an annular combustor with a supersonic flow velocity

A two-dimensional unsteady mathematical model of a continuous spinning detonation wave in a supersonic incoming flow in an annular combustor is formulated. The wave dynamics in a combustor filled by a gaseous hydrogen-oxygen mixture is studied. The possibility of continuous spin detonation with a supersonic flow velocity at the diffuser entrance is demonstrated numerically for the first time; the structure of transverse detonation waves and the range of their existence depending on the Mach number are studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 6, pp. 83–91, November–December, 2008.     

Continuous spin detonation of hydrogen-oxygen mixtures. 1. Annular cylindrical combustors

A comprehensive numerical and experimental study of continuous spin detonation of a hydrogen-oxygen mixture in annular combustors with the components supplied through injectors is performed. In an annular combustor 4 cm in diameter, burning of a hydrogen-oxygen gas mixture in the regime of continuous spin detonation is obtained. The flow structure is considered for varied flow rates of the components of the mixture and the combustor length and shape. The dynamics of the transverse detonation wave is numerically studied in a two-dimensional unsteady statement of the problem with the geometric parameters of the combustors consistent with experimental ones. A comparison with experiments reveals reasonable agreement in terms of the detonation velocity and pressure in the combustor. The calculated size and shape of detonation fronts are substantially different from the experimental data. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 32–45, March–April, 2008.     

Continuous spin detonation of hydrogen-oxygen mixtures. 2. Combustor with an expanding annular channel

A comprehensive numerical and experimental study of continuous spin detonation of a hydrogen-oxygen mixture in an annular combustor with the components supplied through injectors is performed. The hydrogen-oxygen mixture is burned in the regime of continuous spin detonation in an annular combustor 4 cm in diameter with subsequent channel expansion. The flow structure is considered for varied flow rates of the components of the mixture and the counterpressure of the ambient medium. The dynamics of the transverse detonation wave is numerically studied in a two-dimensional unsteady gas-dynamic statement of the problem with the geometric parameters of the combustor consistent with experimental ones. Reasonable agreement with experiments is reached in terms of the shape of detonation fronts, detonation velocity, and height of the wave front. The optimal point of channel expansion beginning is chosen, which ensures the maximum specific impulse in the spin detonation regime. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 95–108, May–June, 2008.     

Numerical Study of Formation of a Detonation Wave in a Supersonic Flow over a Wedge by an H2-O2 Mixture with Nonequilibrium Excitation of Molecular Vibrations of Reagents

Specific features of formation of an oblique detonation wave in a supersonic hydrogen-oxygen mixture flow over a plane wedge are analyzed. Preliminary excitation of molecular vibrations of H₂ is shown to lead to a noticeable (severalfold) decrease in the induction-zone length and the distance at which the detonation wave is formed. These effects are manifested even if H₂ molecules are excited in a narrow region in the vicinity of the flow centerline. The reason for these effects is intensification of chain reactions in the H₂-O₂ (air) mixture owing to the presence of vibrationally excited hydrogen molecules in the flow. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 78–86, January–February, 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.     

Continuous spin detonation of hydrogen-oxygen mixtures. 3. Methods of measuring flow parameters and flow structure in combustors of different geometries

Methods used in studying continuous spin detonation, in particular, in an H₂-O₂ mixture, in annular combustors are considered: optical registration of the regime, pressure measurement, determining the flow rates of gases from finite-volume receivers, determining the velocity of motion of the products, and calculating the flow Mach number in detonation products and the detonation velocity. Experimental and calculated data are compared from the viewpoint of the position of the interface between the subsonic and supersonic flow regions in the combustor and the boundary of the disturbance region above which acoustic disturbances do not penetrate into the combustor. Reasonable agreement between the calculated and experimental positions of these boundaries is reached. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 4, pp. 87–97, July–August, 2008.     

Mathematical modeling of a rotating detonation wave in a hydrogen-oxygen mixture

A two-dimensional unsteady mathematical model of spin detonation in an annular cylindrical ramjet-type combustor is formulated. The wave dynamics in the combustor filled by a hydrogen-oxygen mixture is studied numerically. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 90–101, July–August, 2007.     

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.     

Solid-State Synthesis of ZnTe in Shock Waves

Shock front velocities in a heterogeneous stoichiometric zinc-tellurium mixture in cylindrical capsules were measured at normal and elevated temperatures. In the range of preheating temperatures of 150–300°C, the velocity of a strong shock wave was found to increase by 0.91 km/sec, which is attributed to the occurrence of an exothermic reaction in the zone of high dynamic pressures with an increase in the specific volume. The average velocity of a weak shock wave increased by 0.31 km/sec in the far region of the reaction cell as the preheating temperature of the stoichiometric Zn-Te mixture increased by 150°C. X-ray structure analysis of the shock-recovered products showed almost complete transformation of the reactants with the formation of the cubic ZnTe phase. Theoretical calculations of the acceleration of the shock front velocity due to the reaction in the Zn-Te mixture were conducted. The occurrence of solid-state detonation in the tested mixture is assumed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 130–137, January–February, 2006.     

Experimental investigation of gasless detonation in metal-sulfur compositions

Samples of zinc-sulfur and manganese-sulfur mixtures are shocked using an explosive pentolite charge to investigate if a shock-initiated reaction is able to support continued shock wave propagation. Samples of two different nominal densities (62 and 86% of theoretical maximum density) are prepared as weakly confined cylinders 50 mm in diameter and are instrumented along their length (⩽280 mm) with sensitive piezoelectric pins. Experimental results showed that the shock wave transmitted into the sample by the explosive rapidly decays to an acoustic wave in all four sample types. Furthermore, in denser samples, the part of the sample farthest from the explosive is recovered intact and unreacted, which clearly indicates that the wave is unable to trigger reactions after 100 mm of travel along the sample. Thus, it is concluded that insufficient reaction energy is transmitted forward to the shock wave to prevent its decay as it travels along the sample. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 116–123, March–April, 2009.     

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.     

On the Hydrodynamic Thickness of Cellular Detonations

The characterization of the detonation dynamic parameters (detonability limits, direct initiation energy, critical tube diameter, etc.) requires a characteristic length scale for the detonation wave in the direction of propagation. However, most detonations are unstable, their reaction zones are turbulent, and their structure departs significantly from the idealized one-dimensional Zel'dovich-Von Neumann-Doring model. It is argued that the most suitable length scale to characterize a turbulent detonation wave is the location of the sonic surface, which separates the statistically stationary flow of the reaction zone structure from the unsteady expansions behind the wave. Previous real and numerical experiments are reviewed in order to determine the relation between the global location of the mean sonic surface and the chemical, mechanical, and thermodynamic relaxation processes occurring in the detonation wave structure. Based on the experimental evidence, we postulate that the structure of turbulent detonations can be modeled in the one-dimensional Zel'dovich-Neumann-Doring framework, with the turbulence effects as source terms in the momentum and energy equations. These source terms involve the relaxation rates for the mechanical fluctuations, thermal fluctuations and the chemical exothermicity towards equilibrium. In the framework of the idealized one-dimensional structure with source terms, the sonic surface location is governed by the balance between the competing source terms satisfying the generalized Chapman-Jouguet criterion. We recommend that future work in detonation research should be focused at: 1) acquiring a large experimental database for the mean detonation properties (detonation velocity, location of sonic surface and mean reaction zone profiles); 2) the development of the appropriate source terms involving the turbulent fluctuations in the averaged equations of motion. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 157–180, November–December, 2005.     

Types and stability of detonation flows of aluminum particles in oxygen

The problem of detonation-wave structure is studied on the basis of a mathematical model for the detonation of aluminum particles in oxygen within the framework of a single-velocity two-temperature continuum. An analysis of flow types in the form of the Chapman-Jouguet strong-detonation and weak-detonation regimes is given. A chart of the mixture flow regimes in the plane of the Mach number of the detonation wave and the ratio of the characteristic times of thermal relaxation and combustion is constructed using the results of numerical experiments. The domain of realization of only strong detonation regimes, the manifold of existence of weak and strong detonation regimes, and the domain of nonexistence of stationary solutions are determined. The structural properties of the solutions with an internal singular point and weak structurally unstable regimes with a saddle singularity in the final state are described. The stability of all types of stationary regimes against small and finite perturbations that retain the detonation-wave (DW) velocity and the final state is shown by numerical modeling of nonstationary detonation flows.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 2, pp. 74–85, March–April, 1996.     

Behavior of the vorticity vector in a supersonic nonuniform swirl flow of a combustible gas behind a moving curvilinear shock or detonation wave

Expressions for components of the vorticity vector behind a curvilinear shock or detonation wave propagating in a supersonic nonuniform flow of a combustible gas are derived. Plane and axisymmetric gas flows are considered. The free stream in the general case is a vortex flow with a specified distribution of parameters. Formulas for the vorticity components in the plane of the flow for axisymmetric flows are found to have the same form as formulas for steady axisymmetric flows. As in the case of steady flows, the normal-to-wave component of vorticity is demonstrated to remain continuous across the discontinuity surface; in the case of axisymmetric flows, the ratio of the tangential component of vorticity aligned in the plane of the flow to density also remains continuous, though the quantities themselves become discontinuous. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 68–75, March–April, 2008.     

Effect of an electric field on the stabilization of a turbulent propane—Air flame

The action of an external electric field on the combustion of a premixed propane—air mixture in a turbulent flow is considered. The effect of the geometrical parameters of turbulizing plates, the polarities of the applied voltage, and the diameter of a cylindrical cellular electrode on the magnitude of the flameout velocity is studied. It is shown that the highest flameout velocity is attained with the use of a smaller-diameter electrode and plates generating a large-scale turbulence. The intensities of action of the electric field on laminar and turbulent flames are compared. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 20–24, January–February, 1998.     

Relation between the critical detonation diameter of explosive charges with characteristics of their shock-wave sensitivity

Correlation dependences between the critical diameter of high explosive (HE) charges and characteristics of their shock-wave sensitivity are theoretically justified. Relations for the critical radius of curvature of the detonation-wave front and for the critical detonation diameter are derived on the basis of the author’s theory of the critical diameter and the generalized kinetic characteristic of HE decomposition determined from the experimental dependence of the distance of transition of the initiating shock wave to the detonation wave on the wave amplitude. A qualitative analysis of these relations reveals good agreement with available experimental data. Key words: detonation, critical diameter, sensitivity, shock-wave initiation of detonation, HE decomposition kinetics. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 101–105, May–June, 2009.     

Theory of solid-state detonation

The Jouguet theory allows one to estimate the detonation velocity from the known shock adiabat of the product of a solid-state chemical reaction initiated by a shock wave. Using manganese and zinc chalcogenides as an example, it is shown that such estimates are close to experimental detonation velocities in these systems. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 108–110, March–April, 2007.     

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.     

Reflection of a bubble-detonation wave from a rigid obstacle

The process of detonation-wave reflection from a rigid obstacle in mono- and polydisperse bubble media is studied experimentally. The evolution of the reflected wave formed upon interaction of the detonation wave with the butt-end of a shock tube is traced. The structure of the detonation and reflected waves is studied and the wave pressures are measured at various parameters of the bubble media. The damping constants of the reflected waves are determined. In addition, the velocities of the detonation and reflected waves are measured. The effect of the gas-bubble size on the characteristics of these waves is investigated. The energy-dissipation mechanisms in the detonation and reflected waves in the bubble media are analyzed qualitatively. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 107–113, May–June, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 98-03-32325).