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.     

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.     

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.     

Initiation of detonation of fuel-air mixtures in a flow-type annular combustor

Initiation of detonation in a fuel-air mixture flow formed in an annular cylindrical combustor 306 mm in diameter is studied. The source of detonation initiation is the detonation wave entering the annular channel from a plane-radial vortex chamber, a jet of products, or a low-power heat pulse. It is demonstrated that continuous spin detonation (CSD) can be ensured by all these methods. Its formation is accompanied by a transitional process with a duration up to 10 ms, which is associated with violation of injection of the species (initiation by the detonation wave) or with the time of evolution of tangential instability in CSD (jet or spark initiation). Transfer of detonation to a flow of fuel-air mixtures with low chemical activity (propane-air, methane-air, kerosene-air, and gasoline-air mixtures) by the initiating detonation wave formed within fractions of a millisecond by a low-energy pulse or as a result of self-ignition of the hydrogen-air mixture in the plane-radial vortex chamber is realized. It is found that organization of CSD in these mixtures requires combustors with greater (than 306 mm) diameters. A possibility of CSD in kerosene-air and gasoline-air mixtures with low chemical activity by means of air enrichment by oxygen ahead of the combustor entrance is demonstrated.     

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.     

Detonation properties of the synthesis gas

Investigated parameters of combustion and detonation of mixtures of the synthesis gas with oxygen and air are presented. The ratios between carbon oxide and hydrogen and between the fuels and oxidizer are varied within wide ranges. The critical energy of detonation initiation is determined. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 90–96, November–December, 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.     

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.     

Ignition and combustion of a hydrogen-air mixture in a rapid-compression combustor

In a rapid-compression combustor with a freely moving piston, the efficiency of thermomechanical conversion of energy was determined in the detonation combustion regime of a stoichiometric hydrogen-air mixture under conditions close to those observed during operation of a piston engine of internal combustion in the starting regime. It is shown that this regime of heat release is characterized not only by a dramatic pressure increase in the combustion chamber, but also by its subsequent rapid decrease caused by heat transfer to the cylinder walls and partial condensation of water vapors. The intensity of these components of the thermal process depends progressively on the pressure and temperature of the combustion products, which, in turn, depend on the parameters of the mixture immediately before its ignition. However, the relative increase in combustion pressure turns out to be minimum when the ignition is initiated near the top dead center. It is also shown that the coefficient of thermomechanical conversion of energy (an analog of the indicated efficiency of an internal combustion engine) reaches the maximum value of 31% if the mixture is ignited at a time of approximately 3/4 of a period of oscillations of the piston group after the beginning of compression of an air charge. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 3–14, November–December 1999.     

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.     

Detonation of propane-air mixtures under injection of hot detonation products

The tube for spontaneous detonation (Institute of Technical Physics, Russian Federal Nuclear Center, Snezhinsk) was used to study the initiation and development of detonation in propane-air mixtures under injection of hot detonation products into them. The full picture of this phenomenon was recorded: the injection of hot detonation products into the main tube of the facility with the formation of a mixture of the starting propane-air composition with the hot products; the initiation of a local explosion in this mixture and the subsequent development of a detonation in it; detonation transfer to the region of the cold starting reactants (or detonation failure at the interface). The detonation was found to exist for an initial volume concentration of propane of 3.3 to 5%. The following critical (by the moment of the local explosion) parameters were determined: a mass fraction of hot detonation products of 6–9%, an energy input density due to product injection of 145–195 J/g, and an input energy power of 70–50 J/(g · msec). __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 100–109, May–June, 2006.     

Continuous Spin Detonation in Annular Combustors

An acetylene-oxygen mixture is burned in two annular chambers 100 mm in diameter in the spin detonation regime with supercritical and subcritical differences of oxygen pressure in the annular slot. By varying the flow rates of components of the mixture, width of the slot for oxidizer injection, point of fuel injection, and initial ambient pressure, the regions of existence and the structure of transverse detonation waves are studied, and the limits of existence of continuous detonation in terms of pressure in the chamber are determined. The losses of the total pressure in the flow in oxygen-injection slots and in fuel-injector orifices are estimated.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 4, pp. 99–109, July–August, 2005.     

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.     

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.     

Structure and initiation of plane detonation waves in a bidisperse gas suspension of aluminum particles

Initiation and propagation of plane waves of heterogeneous detonation in a stoichiometric suspension of two fractions of aluminum particles in oxygen are analyzed numerically. It is found that the detonation is not ideal, and the steady-state part of the shock-wave structure is bounded by an equilibrium frozen sonic point. Initiation criteria depend on the particle-size distribution of the mixture. Initiation by explosive shock waves can lead to formation of unstable two-front structures. Addition of a small amount of fine particles into the discrete phase allows the initiation energy to be substantially reduced. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 46–55, March–April, 2008.     

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     

Continuous detonation combustion of fuel-air mixtures

Continuous detonation combustion of fuel-air mixtures was performed. In a disk-shaped chamber with a plane radial eddying flow directed from the periphery to the central outlet opening, a rotating detonation wave in which hydrogen, methane, and sprayed liquid fuels (kerosene and diesel fuel) mixed with air were burnt was excited. Previously, a similar process was realized only for fuel-oxygen mixtures. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 3, pp. 120–131, May–June, 1997.     

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.     

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.     

Combustion of a gasoline-hydrogen-air mixture in a reciprocating internal combustion engine cylinder and determining the optimum gasoline-hydrogen ratio

This paper reports results of an analysis of experimental data on the combustion of a gasoline-hydrogen-air mixture in a reciprocating internal combustion engine cylinder. The completeness of combustion of the mixture is shown to depend on the amount of hydrogen in the fuel mixture and the composition and physicochemical properties of the mixture. In particular, the conditions of addition of hydrogen to the gasoline-air mixture with active chemical action on the combustion process and the action of hydrogen as an additional fuel component are determined. A dimensionless universal relation is proposed that allows one to uniquely determine the initial composition of the fuel mixture (hydrogen to gasoline ratio) to accomplish combustion of the fuel mixture at the lean combustion limit. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 8–14, July–August, 2007.