Continuous detonation in the regime of self-oscillatory ejection of the oxidizer. 2. Air as an oxidizer

Results of an experimental study of continuous detonation of a hydrogen-air mixture in a flow-type annular combustor 306 mm in diameter in the regime of air self-ejection are reported. The regime of pulsed detonation is also obtained. Stable regimes of continuous detonation with one and two transverse detonation waves having velocities D = 1.48−1.16 km/sec are observed in experiments. The frequency of the pulsed detonation wave is ≈1.4 kHz. The known condition for the continuous detonation regime (good mixing for the formation of a detonable layer) is validated. The size of the slot for air ejection, providing a necessary flow rate for detonation and a necessary ratio of the species in the mixture, is determined. Some methods for estimating the air flow rate are presented.     

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.     

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.     

Continuous detonation in the air ejection mode. Domain of existence

Results of an experimental study of continuous and pulsed detonation of a hydrogen-air mixture in an annular flow-type combustor 306 mm in diameter with an expanding channel in the air ejection mode are reported. By varying the free-cross-sectional area of the slot for air supply, the number and cross-sectional area of the orifices of the fuel injectors, the size of the fuel receiver, and the initial pressure of the fuel, the domain of existence of detonation regimes in the coordinates “air ejection slot size versus the specific flow rate of hydrogen” is determined. An optimal air ejection slot width for the combustor and fuel used is found (10–12 mm); deviations from this slot width to either side reduce the domain of existence of detonation regimes. A necessity of making a step in the air supply path is found. It is also shows that there exists an optimal geometry of injector orifices, which expands the domain of existence of detonation regimes. Rough mixing of hydrogen with air, as well as too rapid mixing, makes the domain of detonation existence narrower. The following sequence of processes is found to occur as the hydrogen flow rate is increased: combustion transforms to longitudinal pulsed detonation, then to continuous spin detonation, then to pulsed detonation again, and finally to usual combustion. Experiments of long-time operation of the combustor without cooling are performed.     

Scaling factor in continuous spin detonation of syngas–air mixtures

Multiwave regimes of continuous spin detonation in syngas–air mixtures in a flow-type annular cylindrical combustor 503 mm in diameter are obtained. Experiments are performed for mixtures of carbon oxide and hydrogen with the ratio of the components equal to 1/3, 1/2, or 1/1. The varied parameters are the flow rates of air and syngas, the ratio of these flow rates, and the combustor length. Scalability of the continuous spin detonation process is demonstrated: at identical values of the specific flow rate of air and the combustor expansion ratio, the number of transverse detonation waves increases with increasing combustor diameter. In the examined ranges of combustor lengths and specific flow rates of air, the frequency of these waves is independent of the combustor length, except for narrow regions where the number of waves (and, correspondingly, the flow regime) changes. The structures of transverse detonation waves in regular regimes are almost identical for all examined syngas compositions. It is shown that detonation can be initiated by a jet of combustion products. The minimum diameters of the detonation chamber for different flow rates of the mixture are estimated.     

Detonation combustion of a hydrogen–oxygen mixture in a plane–radial combustor with exhaustion toward the center

Regimes of continuous spin detonation in a plane–radial combustor with an external diameter of 80 mm with peripheral injection of a hydrogen–oxygen mixture in the range of specific flow rates of the mixture 3.6–37.9 kg/(s ·m²) are obtained for the first time. Depending on the diameter of the exit orifice in the combustor (40, 30, or 20 mm), specific flow rate of the mixture, its composition, and counterpressure, one to seven transverse detonation waves with a frequency from 6 to 60 kHz are observed. It is found that the number of detonation waves increases, while their intensity decreases owing to reduction of the exit orifice diameter or to an increase in the counterpressure. The flow structure in the region of detonation waves is analyzed. The domain of detonation regimes in the coordinates of the fuel-to-air equivalence ratio and specific flow rate of the mixture is constructed. A physicomathematical model of continuous spin detonation in a plane–radial combustor is formulated. For parameters of hydrogen and oxygen injection into the combustor identical to experimental conditions, the present simulations predict similar parameters of detonation waves, in particular, the number of waves over the combustor circumference and the wave velocity.     

Continuous spin detonation of a hydrogen-air mixture with addition of air into the products and the mixing region

Results of an experimental study in a flow-type annular cylindrical combustor with an outer diameter of 30.6 cm are described. The influence of air addition to the products of continuous spin detonation of a hydrogen-air mixture and to the mixing region on parameters of detonation waves, pressure in the combustor, and specific impulse is studied. The range of continuous spin detonation of the hydrogen-air mixture is extended to specific flow rates of the mixture equal to 560 kg/(sec · m²) and fuel-to-air equivalence ratios equal to 0.5–4.4. It is demonstrated that addition of air decreases the detonation velocity, increases the pressure in the combustor and thrust, and decreases the specific flow rate of the fuel. The total pressure loss due to the mixing process and heat transfer to a colder gas increases. The minimum specific flow rate of hydrogen reached in the combustor of the examined geometry is 0.04 kg/(h · N).     

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.     

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. 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.     

Realization and modeling of continuous spin detonation of a hydrogen-oxygen mixture in flow-type combustors. 1. Combustors of cylindrical annular geometry

A comprehensive numerical and experimental study of continuous spin detonation of a hydrogen-oxygen mixture in flow-type cylindrical annular combustors 4 and 10 cm in diameter is performed. Hydrogen is injected through injectors, and oxygen is supplied as a continuous flow through an annular slot. The flow structure is studied with variations of the flow rates of the components of the mixture and the width of the slot for oxygen supply. The region of existence of continuous spin detonation is determined as a function of the fuel-to-air equivalence ratio and specific flow rates of the components with variations of the relative width of the slot and combustor diameter. A two-dimensional unsteady gas-dynamic problem of rotation dynamics of a transverse detonation wave with geometric parameters of the combustor corresponding to those used in experiments is solved numerically. A comparison with experiments is performed, and reasonable agreement is reached for the detonation velocity and mean pressure in the combustor. It is shown that the geometric size of the transverse detonation waves is underestimated because the gas-dynamic model does not involve the mixing process, and the number of waves is almost doubled.     

Continuous spin detonation of a coal-air mixture in a flow-type plane-radial combustor

Regimes of continuous spin detonation of coal particles in an air flow in a flow-type plane-radial combustor 500 mm in diameter are studied. The tested substance is fine-grained cannel coal from Kuzbass having a particle size of 1–7 µm and containing 24.7% of volatiles, 14.2% of ashes, and 5.1% of moisture. A certain amount of hydrogen is added for coal transportation into the combustor and promotion of the chemical reaction on the surface of solid particles. To reduce air pressure losses in channels connecting the manifold and the combustor, their cross section is increased to limiting values (25 cm²), whereas the combustor exit diameter is reduced. The angle of the air flow direction and the combustor geometry are also varied. The minimum pressure difference in the air injection channels (16%) is reached with stability of continuous spin detonation in the combustor being retained. The domain of continuous spin detonation regimes in the coordinates of the fuel flow rate and specific flow rate of the mixture is constructed. The results of studying detonation burning of solid fuels can find applications in power engineering, chemical industry, and environmental science, in particular, contamination by combustion products.     

Continuous spin detonation of fuel-air mixtures

Results of an experimental study of controlled continuous spin detonation of acetylene-air and hydrogen-air mixtures, as well as propane-air-oxygen and kerosene-air-oxygen mixtures in a flow-type cylindrical combustor 30.6 cm in diameter are described. The flow structure and the conditions, properties, and areas of existence of continuous detonation are considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 107–115, July–August, 2006.     

Continuous Detonation of Methane/Hydrogen–Air Mixtures in an Annular Cylindrical Combustor

Regimes of continuous detonation of methane/hydrogen–air mixtures in spin and opposing transverse detonation waves are obtained for the first time in a flow-type annular cylindrical combustor 503 mm in diameter. A two-component (methane/hydrogen) fuel with the H₂ mass fractions of 1/9 to 1/2 in the range of specific flow rates of the mixture from 64 to 1310 kg/(s ·m²) and the fuel-to-air equivalence ratio ? = 0.78–1.56 is considered. In methane/hydrogen–air mixtures with two compositions of the fuel (CH₄ + 8H₂ and CH₄ + 4H₂), one-wave and two-wave regimes of continuous spin detonation are obtained; the frequency of rotation of transverse detonation waves is 0.56–1.66 kHz at ? = 0.78–1.02. For the fuel compositions CH₄ + 2H₂ and CH4 + 1.5H2, continuous multifront detonation with two opposing transverse detonation waves rotating with the frequency of 0.86–1.34 kHz at ? = 1.0–1.23 is obtained. For the CH₄ + H₂ + air mixture, both combustion in the chamber and continuous spin detonation outside the combustor with transverse detonation waves rotating with the frequency of 1.01–1.1 kHz are observed. The lean limits of continuous detonation are obtained in terms of the specific flow rate of the mixture: 64, 100, 200, and 790 kg/(s · m²) for the fuel compositions CH₄ + 8H₂, CH₄ + 4H₂, CH₄ + 2H₂, and CH₄ + 1.5H₂, respectively, for the mass fraction of hydrogen in the methane/hydrogen fuel of ≈0.16. Violation of regularity of the continuous detonation wave structure and the wave velocity with a decrease in the fraction of hydrogen in the two-component fuel is detected.     

Realization and modeling of continuous spin detonation of a hydrogen-oxygen mixture in flow-type combustors. 2. Combustors with expansion of the annular channel

Results of a comprehensive numerical and experimental study of continuous spin detonation of an H₂-O₂ mixture in flow-type annular combustors with channel expansion are presented. In these experiments, oxygen is supplied as a continuous flow through an annular slot, and hydrogen is injected through injectors. Combustion of hydrogen-oxygen mixtures in continuously rotating (spinning) and pulsed detonation waves with exhaustion of the products into an evacuated tank with increasing counterpressure and into the atmosphere was realized and studied in such combustors for the first time. The domain of realization of continuous detonation is determined. Verification of the mathematical model is performed on the basis of experimental results, and reasonable agreement is reached for the basic detonation parameters: structure of transverse detonation waves, their velocity, and pressures in the combustor and in the injection system.     

Detonation Velocity of Emulsion Explosives Containing Cenospheres

The detonation velocity of an emulsion explosive containing hollow alumosilicate microspheres (cenospheres) as the sensitizer is measured. The size of the microspheres is 50–250 μm. The relations between the detonation velocity and the charge density and diameter are compared for emulsion explosives containing cenospheres or glass microballoons as the sensitizer. It is shown that for a 55 mm diameter charge, the maximum detonation velocity of the composition with cenospheres of size 70–100 μm is 5.5–5.6 km/sec, as well as for 3M glass microballoons. The critical diameter for the emulsion explosive with cenosphere is 1.5–2 times larger than that for the emulsion explosive with glass microballoons and is 35–40 mm. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 119–127, September–October, 2005.     

Energy release of mixed explosives during propagation of a nonideal detonation under conditions similar to the operation conditions of a blasthole charge

Detonation experiments were performed in a specially developed explosive device simulating a blasthole using charges of fine-grained and coarse-grained (granular) 30/70 TNT/ammonium nitrate mixtures of identical density 0.89 g/cm³ in steel shells with an inner diameter of 28 mm and a wall thickness of 3 mm at detonation velocities of 4.13 and 2.13 km/sec, respectively. Despite significant differences in detonation velocity (pressure), identical expansion of the charge shells was observed. On the other hand, numerical simulations of detonation propagation in the explosive device with the corresponding velocities ignoring the possibility of energy release behind the shock front show that the expansion of the charge shell is always greater in the case of a high-velocity regime. It is concluded that under the conditions simulating detonation propagation and the work of explosion products in a blasthole, effective additional energy release occurs behind the low-velocity (nonideal) detonation front. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 111–120, July–August, 2007.     

Continuous spin detonation of synthesis gas-air mixtures

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 oxide-hydrogen 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 ratio-specific flow rate of the mixture.     

Reactive thrust generated by continuous detonation in the air ejection mode

Processes of continuous spin detonation and pulsed detonation, as well as combustion of a hydrogen-air mixture in an annular combustor 306 mm in diameter in the regime of air ejection are studied experimentally. The specific flow rates of hydrogen are 0.6–9.8 kg/(s ·m²). It is found that the greatest specific impulses of thrust generated by the combustor are reached in the case of continuous spin detonation. On the average, they are greater than the corresponding values by a factor of 1.5 in the case of burning the mixture in streamwise detonation waves, by a factor of 2 in the case of conventional combustion (by a factor of 3 at the maximum thrust impulse of 2200 m/s), and by a factor of 10 in the case of exhaustion of cold hydrogen. A change in the specific flow rate of hydrogen beginning from ≈1.2 kg/(s·m²) corresponding to the maximum thrust impulse decreases its value, and this decrease is more profound as the detonation limits in terms of the specific flow rate of hydrogen are approached. The maximum reactive thrust (83 N) is developed in the examined detonation chamber near the upper limit at the specific flow rate of hydrogen equal to 3 kg/(s·m²).