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.     

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.     

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.     

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).     

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.     

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 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.     

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.     

Pressure measurement by fast-response piezo-electric sensors during continuous spin detonation in the combustor

Pressure profiles in a transverse detonation wave propagating in a plane-radial vortex chamber during continuous spin detonation of a mixture consisting of lignite, syngas, and air are measured by specially designed and fabricated high-frequency pressure sensors based on TsTS-19 piezo-ceramics. Pressure levels in the detonation wave front relative to the mean static pressure are determined. It is demonstrated that these levels decrease toward the combustor center (by a factor of 20 and lower) as the wave intensity (velocity) decreases. Pressure oscillations behind the wave front testify to a complex gas-dynamic pattern of the processes in the wave region. A chemical reaction region is detected behind the wave front; its length is approximately 8% of the period between the waves.     

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.     

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 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.     

Characteristics of diesel fuel combustion in a burner with injection of a superheated steam jet

Basic characteristics of combustion of the diesel fuel in a novel autonomous burner with injection of superheated steam into the combustion region are studied. The temperature distribution in the flame is obtained. Calorimetric measurements of heat release and gas analysis of combustion products are performed. The environmental effects of fuel combustion are compared for regimes with injection of a steam jet and an air jet. It is demonstrated that the combustion regime with steam gasification ensures high combustion intensity and combustion efficiency; moreover, the combustion process becomes more environmentally friendly.     

Splitting flames in a narrow channel with a temperature gradient in the walls

A possibility of simultaneous formation of two chemical reaction fronts during nonstationary combustion of a gas in a microchannel with a temperature gradient in the walls is demonstrated. Combustion in a straight tube and in a gap between two disks with radial fuel injection is considered. In both cases, the characteristic transverse size of the channel is smaller than the critical diameter determined for the ambient temperature, and gas combustion occurs in the region where the wall temperature is higher than the ambient temperature. A numerical study of flame repetitive extinction/ignition (FREI) demonstrated a possibility of simultaneous formation of two chemical reaction fronts in the hot region of the channel. One front corresponds to conventional flame propagating upstream from the hot to the cold part of the channel, and the other front moves in the downstream direction and decays as the fuel burns out. Based on this study, a new mechanism of ignition and incomplete combustion of the combustible mixture in microsystems is proposed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 12–19, March–April, 2008.     

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 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.     

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.     

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).     

Experimental and numerical studies of mixing and flame stability in a micro-cyclone combustor

A 30-W-class micro-cyclone combustor was developed as a heat source for a 1-W thermoelectric power generator (TPG). Methane gas was used as a fuel instead of liquefied fuel in this feasibility study for convenience. The combustion stability of the combustor was measured, and the flame shapes were visualized experimentally. Numerical simulations were performed to examine the details of the flame structure and flame stabilization mechanism inside the micro-cyclone combustor. The micro-cyclone combustor burned the supplied fuel stably inside the combustion chamber in the range where the combustor generated 30 W of heat energy. The mixing and flow characteristics of non-reacting and reacting flows in the combustor were examined using the simulation results. The mixing of the fuel with air in a non-reacting flow field was enhanced by increasing the equivalence ratio for a fixed fuel flow rate. For non-reacting flow, a recirculation region and a small negative axial velocity region near the injection ports were formed. The recirculation region became wider with decreasing equivalence ratios. For reacting flows, however, the recirculation region disappeared and the only small negative axial velocity region was formed near the fuel injection ports. The flame was stabilized inside the combustor because the flame base was anchored near the negative axial velocity region near the fuel injection ports.     

Modeling of Plane Detonation Waves in a Gas Suspension of Aluminum Nanoparticles

A physicomathematical model of detonation of a gas suspension of aluminum nanoparticles with allowance for the transition from the continuum to free-molecular flow regime and heat transfer between the particles is proposed. A formula for logarithmic interpolation for the thermal relaxation time in the transitional regime is derived. A semi-empirical model of Arrheniustype reduced kinetics of combustion is developed, which ensures good agreement with available experimental data. Steady (Chapman–Jouguet and overdriven) structures and also attenuating detonation waves in suspensions of nanoparticles are analyzed. Typical features of detonation in nanoparticle suspensions are found: the normal detonation regimes correspond to the solution in the Chapman–Jouguet plane with a sonic final state in terms of the equilibrium velocity of sound; combustion occurs in an almost equilibrium mixture in terms of velocities and temperatures; a strong dependence of the combustion region length on the amplitude of the leading shock wave is observed.