2019 Vol. 39, No. 11
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2019, 39(11): 112101.
doi: 10.11883/bzycj-2018-0410
Abstract:
This paper offers a new method for calculating the reaction rate of the pore collapse hot-spot ignition in multi-component PBX explosives, and proposes a new mesoscopic reaction rate model capable of describing and predicting the shock initiation and detonation behavior of multi-component PBX explosives with any explosive components proportion as well as any explosive particle size. The pressure-time histories in the explosive samples calculated using this mesoscopic reaction rate model are in good agreement with the experimental data. The shock initiation and detonation process of PBX explosives is mainly controlled by both the hot-spot ignition processes and the combustion reaction processes. The PBXC03 explosive with the dominant component of HMX is mainly controlled by the hot-spot ignition and shows the accelerated reaction characteristics. With the dominant component of insensitive TATB, the critical initiation pressure of PBXC10 is high and the shock initiation behavior is controlled by the combustion reaction process, which shows a stable reaction characteristics.
This paper offers a new method for calculating the reaction rate of the pore collapse hot-spot ignition in multi-component PBX explosives, and proposes a new mesoscopic reaction rate model capable of describing and predicting the shock initiation and detonation behavior of multi-component PBX explosives with any explosive components proportion as well as any explosive particle size. The pressure-time histories in the explosive samples calculated using this mesoscopic reaction rate model are in good agreement with the experimental data. The shock initiation and detonation process of PBX explosives is mainly controlled by both the hot-spot ignition processes and the combustion reaction processes. The PBXC03 explosive with the dominant component of HMX is mainly controlled by the hot-spot ignition and shows the accelerated reaction characteristics. With the dominant component of insensitive TATB, the critical initiation pressure of PBXC10 is high and the shock initiation behavior is controlled by the combustion reaction process, which shows a stable reaction characteristics.
2019, 39(11): 112102.
doi: 10.11883/bzycj-2018-0482
Abstract:
The influence of orifice plate perturbation on detonation cellular structure was experimentally investigated. The cellular structure of detonation wave was recorded in a circular detonation tube withthe smoked film method.The stable mixture 2H2+O2+3Ar and unstable mixture C2H2+5N2O and CH4+2O2 were used. The correlation between cell size and initial pressure was obtained. The variations of cellular structure upstream and downstream of perturbation were studied, and influence of cellular instability oncellular structure characteristics was analyzed. The characteristic length scaleofdetonation recovery from perturbation was obtained. The results show that after the perturbation the main cell structure becomes irregular when no secondary cells appearfor the stable mixture,while for the unstable mixture, the secondary modes of the detonation wave downstream of the perturbationareinitially suppressed, subsequently the local explosions and fine cellsare generated due to the cellular instability. The detonation wave propagates some distance and recovers to the equilibrium state. This characteristic length varies within the range of 8 to 15 timesthe cell size, while it does not change with the initial pressure. The resultimplies that the characteristic length scale of the detonation wave recovery fromthe perturbationequatesto the detonation hydrodynamic thickness.
The influence of orifice plate perturbation on detonation cellular structure was experimentally investigated. The cellular structure of detonation wave was recorded in a circular detonation tube withthe smoked film method.The stable mixture 2H2+O2+3Ar and unstable mixture C2H2+5N2O and CH4+2O2 were used. The correlation between cell size and initial pressure was obtained. The variations of cellular structure upstream and downstream of perturbation were studied, and influence of cellular instability oncellular structure characteristics was analyzed. The characteristic length scaleofdetonation recovery from perturbation was obtained. The results show that after the perturbation the main cell structure becomes irregular when no secondary cells appearfor the stable mixture,while for the unstable mixture, the secondary modes of the detonation wave downstream of the perturbationareinitially suppressed, subsequently the local explosions and fine cellsare generated due to the cellular instability. The detonation wave propagates some distance and recovers to the equilibrium state. This characteristic length varies within the range of 8 to 15 timesthe cell size, while it does not change with the initial pressure. The resultimplies that the characteristic length scale of the detonation wave recovery fromthe perturbationequatesto the detonation hydrodynamic thickness.
2019, 39(11): 112201.
doi: 10.11883/bzycj-2018-0287
Abstract:
In order to predict the intense blast wave in air, a multi-material numerical scheme is proposed in two-dimensional cylindrical coordinates on Eulerian grids, which can handle the blast wave problems with high ratio in initial density and pressure. Combined with the adaptive mesh technique, the propagation of blast wave produced by a 1 kt TNT intense explosion is simulated, and the effects of real gas equation of state and the nonuniform atmosphere are taken into account. The calculated blast wave parameters on the ground, such as peak overpressures and impulses, agree well with the experimental data in a wide space range, and the influences of heights of burst are analyzed.
In order to predict the intense blast wave in air, a multi-material numerical scheme is proposed in two-dimensional cylindrical coordinates on Eulerian grids, which can handle the blast wave problems with high ratio in initial density and pressure. Combined with the adaptive mesh technique, the propagation of blast wave produced by a 1 kt TNT intense explosion is simulated, and the effects of real gas equation of state and the nonuniform atmosphere are taken into account. The calculated blast wave parameters on the ground, such as peak overpressures and impulses, agree well with the experimental data in a wide space range, and the influences of heights of burst are analyzed.
2019, 39(11): 113101.
doi: 10.11883/bzycj-2018-0506
Abstract:
In order to obtain the effect of meso-structure on plain/reinforced concrete slabs under explosive loading, a meso-structure model of plain/reinforced concrete slabs with stochastic aggregate method was adopted. LS-DYNA was used for numerical simulation of reinforced concrete slabs based on meso-modeling under explosive loading. The accuracy of the meso-modeling method was verified by comparing with the experimental and homogeneous modeling methods. Furthermore, the structural dynamic response of plain/reinforced concrete slabs based on meso-modeling under different explosive loads was studied, and the response process and failure mode of plain/reinforced concrete slabs were obtained. The results show that the meso-structure has little effect on the plain/reinforced concrete slab under low explosive loading (1 kg and 2 kg). The failure mode is mainly based on the vertical and horizontal plastic hinge damage. The larger the dose, the more the hinge line. Comparatively, the meso-structure has a great influence on the plain/reinforced concrete slab under the high explosive load (5 kg, 10 kg and 15 kg), and there is a big difference compared with the homogeneous model. The plain/reinforced concrete slab is centered on the blasting pit and produces circumferential and radial cracks under high explosive loading (5 kg, 10 kg and 15 kg). The larger the dose, the larger the round pit, the more cracks, the more serious the local damage.
In order to obtain the effect of meso-structure on plain/reinforced concrete slabs under explosive loading, a meso-structure model of plain/reinforced concrete slabs with stochastic aggregate method was adopted. LS-DYNA was used for numerical simulation of reinforced concrete slabs based on meso-modeling under explosive loading. The accuracy of the meso-modeling method was verified by comparing with the experimental and homogeneous modeling methods. Furthermore, the structural dynamic response of plain/reinforced concrete slabs based on meso-modeling under different explosive loads was studied, and the response process and failure mode of plain/reinforced concrete slabs were obtained. The results show that the meso-structure has little effect on the plain/reinforced concrete slab under low explosive loading (1 kg and 2 kg). The failure mode is mainly based on the vertical and horizontal plastic hinge damage. The larger the dose, the more the hinge line. Comparatively, the meso-structure has a great influence on the plain/reinforced concrete slab under the high explosive load (5 kg, 10 kg and 15 kg), and there is a big difference compared with the homogeneous model. The plain/reinforced concrete slab is centered on the blasting pit and produces circumferential and radial cracks under high explosive loading (5 kg, 10 kg and 15 kg). The larger the dose, the larger the round pit, the more cracks, the more serious the local damage.
2019, 39(11): 113301.
doi: 10.11883/bzycj-2018-0402
Abstract:
Whether the replica scaling law holds or not is of great significance because penetration tests of concrete targets against rigid projectiles are commonly conducted in a reduced scale. In this paper, based on the replica scaling model and the analyses of penetration tests with various sizes and empirical formulae, we found that there exists a size effect in general for penetration depth, and the dimensionless depth increases with as does the size. However, the replica scaling law is satisfied for the penetration depth in rigid projectile penetrations, as long as the scaling is done strictly for both projectiles and concrete targets, including the coarse aggregates. We also found that the coarse aggregates of an invariant size (not replica-scaled) are the major factor accounting for the size effect in penetration depth found in tests and empirical formulae. To find out about the size effect resulting from aggregates, we developed a 2D mesoscopic finite element model for concrete target and conducted numerical simulations that successfully represent the size effect, thereby proving that penetration formula with size effect considered could well predict the penetration tests with different size.
Whether the replica scaling law holds or not is of great significance because penetration tests of concrete targets against rigid projectiles are commonly conducted in a reduced scale. In this paper, based on the replica scaling model and the analyses of penetration tests with various sizes and empirical formulae, we found that there exists a size effect in general for penetration depth, and the dimensionless depth increases with as does the size. However, the replica scaling law is satisfied for the penetration depth in rigid projectile penetrations, as long as the scaling is done strictly for both projectiles and concrete targets, including the coarse aggregates. We also found that the coarse aggregates of an invariant size (not replica-scaled) are the major factor accounting for the size effect in penetration depth found in tests and empirical formulae. To find out about the size effect resulting from aggregates, we developed a 2D mesoscopic finite element model for concrete target and conducted numerical simulations that successfully represent the size effect, thereby proving that penetration formula with size effect considered could well predict the penetration tests with different size.
2019, 39(11): 113901.
doi: 10.11883/bzycj-2018-0315
Abstract:
The numerical simulation of oblique water entry of a certain type of ship-borne projectile at high speed was performed. The FVM method and the VOF multiphase flow model were introduced to solve RANS equations, and the overset mesh and six DOF algorithms were used to achieve the coupling solution of the movement of projectile and the multiphase flow field. Based on this method, the influence of projectile rotation effect on the projectile motion characteristics and hydrodynamic characteristics was firstly studied. And then the cavitation morphology, the ballistic and hydrodynamic characteristics during the oblique water entry of the rotating projectile at different inclination angles were analyzed. The simulation results shows that the rotation of the projectile is beneficial to the ballistic stability of the projectile in the initial symmetric plane, but it reduces the lateral stability of the projectile. The rotation of projectile reduces the drag coefficient and pitching moment coefficient of the projectile. With smaller initial water entry angle, the cavitation shape was more asymmetric, and the change of cavitation shape caused by the change of projectile motion state was more obvious. At the stage of supercavitation, the motion of the projectile was relatively stable, and the hydrodynamic coefficients has minor difference at different angles. When the lower surface of the projectile pierced the cavity wall and wetted, the motion state of the projectile changed greatly and the hydrodynamic coefficients increased rapidly, and at this stage, the projectile are prone to becoming unstable if the water entry angle is too small. The wetting of the projectile has an important influence on the cavitation shape, motion state and stability of the projectile.
The numerical simulation of oblique water entry of a certain type of ship-borne projectile at high speed was performed. The FVM method and the VOF multiphase flow model were introduced to solve RANS equations, and the overset mesh and six DOF algorithms were used to achieve the coupling solution of the movement of projectile and the multiphase flow field. Based on this method, the influence of projectile rotation effect on the projectile motion characteristics and hydrodynamic characteristics was firstly studied. And then the cavitation morphology, the ballistic and hydrodynamic characteristics during the oblique water entry of the rotating projectile at different inclination angles were analyzed. The simulation results shows that the rotation of the projectile is beneficial to the ballistic stability of the projectile in the initial symmetric plane, but it reduces the lateral stability of the projectile. The rotation of projectile reduces the drag coefficient and pitching moment coefficient of the projectile. With smaller initial water entry angle, the cavitation shape was more asymmetric, and the change of cavitation shape caused by the change of projectile motion state was more obvious. At the stage of supercavitation, the motion of the projectile was relatively stable, and the hydrodynamic coefficients has minor difference at different angles. When the lower surface of the projectile pierced the cavity wall and wetted, the motion state of the projectile changed greatly and the hydrodynamic coefficients increased rapidly, and at this stage, the projectile are prone to becoming unstable if the water entry angle is too small. The wetting of the projectile has an important influence on the cavitation shape, motion state and stability of the projectile.
2019, 39(11): 113902.
doi: 10.11883/bzycj-2018-0498
Abstract:
In this work we conducted comparative experiments of different truncated cone-nosed projectiles entering water at low-speed and oblique inclination to investigate the influence of the size of the head diameter on water-entry cavity and ballistic characteristics using high-speed photography. We observed and recorded the effects of the size of the head diameter on the cavitational evolution, velocity and pitch angle of the truncated cone-nosed projectiles. The following results were achieved: the larger the truncated cone head projectile diameter, the earlier the tail collides with the low surface cavity; the size of the head diameter has little effect on the cavity deep closure moment; the cavity of projectile increases with the increase of the head diameter; an excessively large or small head diameter is not conducive to the stability of water entry; when the water entry velocity of the projectile is below the critical velocity, the velocity shows an upward trend, while when it is above the critical velocity, it will show a downward trend.
In this work we conducted comparative experiments of different truncated cone-nosed projectiles entering water at low-speed and oblique inclination to investigate the influence of the size of the head diameter on water-entry cavity and ballistic characteristics using high-speed photography. We observed and recorded the effects of the size of the head diameter on the cavitational evolution, velocity and pitch angle of the truncated cone-nosed projectiles. The following results were achieved: the larger the truncated cone head projectile diameter, the earlier the tail collides with the low surface cavity; the size of the head diameter has little effect on the cavity deep closure moment; the cavity of projectile increases with the increase of the head diameter; an excessively large or small head diameter is not conducive to the stability of water entry; when the water entry velocity of the projectile is below the critical velocity, the velocity shows an upward trend, while when it is above the critical velocity, it will show a downward trend.
2019, 39(11): 113201.
doi: 10.11883/bzycj-2018-0247
Abstract:
A multitude of flaws always exists in brittle material and the influence will be exerted on by other flaws when one flaw is propagating. To investigate the propagation, coalition behavior and stress intensity factors of two cracks in brittle materials under impact loading, Polymethyl methacrylate (PMMA) was selected to manufacture the double cracked specimens. By using the medium-low speed impact system, impact experiments were conducted, and the crack tip SIFs were calculated by using finite element code ABAQUS. The finite difference code AUTODYN was used in the simulation crack propagation behavior, and the simulation results were compared with the test results. The results of experiment and simulation show that the simulation results generally agree with the experimental results in crack propagation paths; the crack propagation behavior varies with the change of the distance between the two cracks; the effect between the two cracks decreases with the increase of the distance between the two cracks; the stress intensity factors KI decrease with the increase of the distance between the two cracks while KII is the opposite.
A multitude of flaws always exists in brittle material and the influence will be exerted on by other flaws when one flaw is propagating. To investigate the propagation, coalition behavior and stress intensity factors of two cracks in brittle materials under impact loading, Polymethyl methacrylate (PMMA) was selected to manufacture the double cracked specimens. By using the medium-low speed impact system, impact experiments were conducted, and the crack tip SIFs were calculated by using finite element code ABAQUS. The finite difference code AUTODYN was used in the simulation crack propagation behavior, and the simulation results were compared with the test results. The results of experiment and simulation show that the simulation results generally agree with the experimental results in crack propagation paths; the crack propagation behavior varies with the change of the distance between the two cracks; the effect between the two cracks decreases with the increase of the distance between the two cracks; the stress intensity factors KI decrease with the increase of the distance between the two cracks while KII is the opposite.
2019, 39(11): 115101.
doi: 10.11883/bzycj-2018-0237
Abstract:
A kind of hollow reinforced concrete column with inner octagon steel tube is considered as the object of this study. The experiments are carried out using a large drop testing machine which was designed by ourselves. The analysis parameters included the boundary conditions, the impact heights and the axial compression ratios. During the experiments, the time history curves of the impact force and the lateral deformation of specimens were recorded. As well as, the failure forms of specimens were observed after the impact tests. A common hollow reinforced concrete specimen was selected and compared with the hollow reinforced concrete column with inner octagon steel tube under the same conditions. The results show that the impact resistance of the hollow reinforced concrete columns with inner octagon steel tube is obviously better than that of the corresponding hollow reinforced concrete columns by using the inner steel tube instead of the built-in steel cage. Within the range of axial compression ratio not exceeding 0.3, the change of axial compression ratio has little effect on the residual deflection of hollow reinforced concrete columns with inner octagon steel tube after impact.
A kind of hollow reinforced concrete column with inner octagon steel tube is considered as the object of this study. The experiments are carried out using a large drop testing machine which was designed by ourselves. The analysis parameters included the boundary conditions, the impact heights and the axial compression ratios. During the experiments, the time history curves of the impact force and the lateral deformation of specimens were recorded. As well as, the failure forms of specimens were observed after the impact tests. A common hollow reinforced concrete specimen was selected and compared with the hollow reinforced concrete column with inner octagon steel tube under the same conditions. The results show that the impact resistance of the hollow reinforced concrete columns with inner octagon steel tube is obviously better than that of the corresponding hollow reinforced concrete columns by using the inner steel tube instead of the built-in steel cage. Within the range of axial compression ratio not exceeding 0.3, the change of axial compression ratio has little effect on the residual deflection of hollow reinforced concrete columns with inner octagon steel tube after impact.
2019, 39(11): 115102.
doi: 10.11883/bzycj-2018-0500
Abstract:
In this work we carried out a lateral impact test of steel reinforced concrete (SRC) members using a super heavy drop weight impact tester, studied the whole process of impact and the ultimate failure mode of drop weight impacted SRC members, and analyzed the time history curves of the impact force, the displacement and the axial force, with the effects of different impact velocities, impact energies, axial pressures and boundary conditions on the dynamic response of SRC members compared. The following results were achieved: the outer concrete of the SRC members is seriously damaged under drop weight impact; the larger the impact energy of the drop weight, the more likely the shear failure of the outer concrete; the internal rebar and H-shaped steel only have a limited bending deformation; and the impact resistance of SRC is generally good. Within the parameters of this test, the impact force and the mid-span displacement of SRC increase with the increase of the impact velocity; the increase of the axial pressure increases the peak value of the impact of SRC, and the impact time and mid-span displacement decrease. Compared with the boundary conditions of one fixed end, one simply supported end and the two simple supported ends, the boundary of the two fixed ends is the best for the impact resistance of SRC.
In this work we carried out a lateral impact test of steel reinforced concrete (SRC) members using a super heavy drop weight impact tester, studied the whole process of impact and the ultimate failure mode of drop weight impacted SRC members, and analyzed the time history curves of the impact force, the displacement and the axial force, with the effects of different impact velocities, impact energies, axial pressures and boundary conditions on the dynamic response of SRC members compared. The following results were achieved: the outer concrete of the SRC members is seriously damaged under drop weight impact; the larger the impact energy of the drop weight, the more likely the shear failure of the outer concrete; the internal rebar and H-shaped steel only have a limited bending deformation; and the impact resistance of SRC is generally good. Within the parameters of this test, the impact force and the mid-span displacement of SRC increase with the increase of the impact velocity; the increase of the axial pressure increases the peak value of the impact of SRC, and the impact time and mid-span displacement decrease. Compared with the boundary conditions of one fixed end, one simply supported end and the two simple supported ends, the boundary of the two fixed ends is the best for the impact resistance of SRC.
2019, 39(11): 115103.
doi: 10.11883/bzycj-2018-0320
Abstract:
As the road plays a more important role in the missile’s unsupported random launch, it is of great significance to study the settlement and damage characteristics under the impulse load of the launching cylinder to improve the weapon deterrent force of China. The object of study is low grade road structure. Firstly, based on the statistical information of low-grade road structures in Henan, Shandong, Yunnan and Guangdong provinces, a 1/4 simplified calculation model for typical low-grade road structures is established. An explicit numerical analysis method CDEM based on FEM and DEM is introduced, and a plastic-localized-rupture coupled constitutive model is introduced to realize three-dimension full-time simulation of pavement settlement under impulse load, explicitly reveal the process of crack initiation and expansion, and realize the transition of the pavement structure from continuous state to discontinuous state. The correctness of the road numerical model and the calculation accuracy of CDEM are verified by comparing with the results of Falling Weight Deflectometer. Then the typical asphalt concrete and cement concrete road structures are selected for numerical simulation and analyzed from the aspects of the settlement, fracture degree and damage characteristics. The results show that the settlement time-history curve is consistent with the trend of the impulse load, and the settlement reaches the maximum at the peak point of the impulse load; the fracture surface is mainly generated during the period of sharp increase of the impulse load, accounting for 97% of the final total fracture area; the fracture surface is roughly divided into the vertical surface in the layer and the horizontal fracture surface between the layers, the failure type includes tensile failure and shear failure; the upper part of the pavement structure produces an annular fracture surface, and the lower part produces a radial fracture surface.
As the road plays a more important role in the missile’s unsupported random launch, it is of great significance to study the settlement and damage characteristics under the impulse load of the launching cylinder to improve the weapon deterrent force of China. The object of study is low grade road structure. Firstly, based on the statistical information of low-grade road structures in Henan, Shandong, Yunnan and Guangdong provinces, a 1/4 simplified calculation model for typical low-grade road structures is established. An explicit numerical analysis method CDEM based on FEM and DEM is introduced, and a plastic-localized-rupture coupled constitutive model is introduced to realize three-dimension full-time simulation of pavement settlement under impulse load, explicitly reveal the process of crack initiation and expansion, and realize the transition of the pavement structure from continuous state to discontinuous state. The correctness of the road numerical model and the calculation accuracy of CDEM are verified by comparing with the results of Falling Weight Deflectometer. Then the typical asphalt concrete and cement concrete road structures are selected for numerical simulation and analyzed from the aspects of the settlement, fracture degree and damage characteristics. The results show that the settlement time-history curve is consistent with the trend of the impulse load, and the settlement reaches the maximum at the peak point of the impulse load; the fracture surface is mainly generated during the period of sharp increase of the impulse load, accounting for 97% of the final total fracture area; the fracture surface is roughly divided into the vertical surface in the layer and the horizontal fracture surface between the layers, the failure type includes tensile failure and shear failure; the upper part of the pavement structure produces an annular fracture surface, and the lower part produces a radial fracture surface.
2019, 39(11): 115401.
doi: 10.11883/bzycj-2018-0236
Abstract:
In order to develop green, eco-friendly and highly efficient explosion suppression agent, hydrophobic fumed silica and deionized water are used as the raw materials to prepare novel dry water materials with " water encapsulation by solid” structure by a mechanically stirring method. A 20 L near-spherical explosive device is employed to test the explosion suppression effect of dry water materials on methane deflagration. The experimental results show that, when the mass of the added dry water materials is 2 g and 3 g, it has a promoting effect on the gas deflagration; when the mass of dry water materials is more than 4 g, it has a suppression effect on gas deflagration. The effect of particle size of dry water on the inhibition performance is investigated. The particle size of dry water materials has less influence on the maximum deflagration pressure, but it greatly influences the maximum deflagration pressure rising rate. The explosion suppression performances of the modified dry water materials are compared with that of pure dry water. The suppression effects are ordered from strong to weak as: urea-modified dry water materials, ammonium dihydrogen phosphate-modified dry water materials, ammonium polyphosphate-dry water materials and pure dry water materials.
In order to develop green, eco-friendly and highly efficient explosion suppression agent, hydrophobic fumed silica and deionized water are used as the raw materials to prepare novel dry water materials with " water encapsulation by solid” structure by a mechanically stirring method. A 20 L near-spherical explosive device is employed to test the explosion suppression effect of dry water materials on methane deflagration. The experimental results show that, when the mass of the added dry water materials is 2 g and 3 g, it has a promoting effect on the gas deflagration; when the mass of dry water materials is more than 4 g, it has a suppression effect on gas deflagration. The effect of particle size of dry water on the inhibition performance is investigated. The particle size of dry water materials has less influence on the maximum deflagration pressure, but it greatly influences the maximum deflagration pressure rising rate. The explosion suppression performances of the modified dry water materials are compared with that of pure dry water. The suppression effects are ordered from strong to weak as: urea-modified dry water materials, ammonium dihydrogen phosphate-modified dry water materials, ammonium polyphosphate-dry water materials and pure dry water materials.
2019, 39(11): 115402.
doi: 10.11883/bzycj-2018-0394
Abstract:
In this paper, to investigate the variation of the critical initial release pressure with the pipeline length in high-pressure hydrogen leakage that leads to spontaneous combustion and the transition process from spontaneous combustion flame inside the tube to the jet flame outside the tube, we conducted experiments using a pressure gauge, a photoelectric and high-speed camera, etc. Our results showed that, at the same pipeline length and under a low initial release pressure, hydrogen is not apt to spontaneous combustion. The minimum initial release pressure of hydrogen spontaneous combustion decreases slowly and then increases rapidly with as the pipe length increases. At the same pipeline length, the greater the initial release pressure, the faster the shock wave propagation, and the closer the hydrogen self-ignition position inside the pipe to the rupture disc. It is found that the flame combustion is intensified after the airflow passed through the Mach disk. With the increase of time, the flame length increases first and then decreases gradually, the average propagation speed of the jet flame tip decreases gradually. The flame width increases first and then decreases rapidly to a stable value.
In this paper, to investigate the variation of the critical initial release pressure with the pipeline length in high-pressure hydrogen leakage that leads to spontaneous combustion and the transition process from spontaneous combustion flame inside the tube to the jet flame outside the tube, we conducted experiments using a pressure gauge, a photoelectric and high-speed camera, etc. Our results showed that, at the same pipeline length and under a low initial release pressure, hydrogen is not apt to spontaneous combustion. The minimum initial release pressure of hydrogen spontaneous combustion decreases slowly and then increases rapidly with as the pipe length increases. At the same pipeline length, the greater the initial release pressure, the faster the shock wave propagation, and the closer the hydrogen self-ignition position inside the pipe to the rupture disc. It is found that the flame combustion is intensified after the airflow passed through the Mach disk. With the increase of time, the flame length increases first and then decreases gradually, the average propagation speed of the jet flame tip decreases gradually. The flame width increases first and then decreases rapidly to a stable value.
2019, 39(11): 115403.
doi: 10.11883/bzycj-2018-0228
Abstract:
To investigate the effect of blockage ratios (φ) on the inhibited flame, an experimental study was performed to suppress the methane-air explosions in a 5 L duct with the blockage ratios φ = 0, 0.2, 0.4, 0.6, 0.7, 1.0 under BC and Al(OH)3 inhibitors with the mass concentrations C = 0 g/m3, 80 g/m3, 160 g/m3 and 240 g/m3. The results indicated that the flame fragmentation increased with the improvement of the suppression efficiency. The maximum explosion pressure (pmax) and the deflagration index of the explosion (Kst) were dominated by the combustion rate and the discharge rate. Furthermore, φ = 0.7 was the inflection point of pmax and Kst curves. The drop rate in the Pmax (δ) firstly increased and then decreased as the blockage ratio increased. And the maximum δmax was achieved at the blockage ratio between 0.4 with 0.6. In general, the suppression efficiency of Al(OH)3 and NaHCO3 powders was comparable. However, the low turbulence caused by certain blocking ratios impacted the sedimentation of inhibitor particles, which made the suppression efficiency of Al(OH)3 better than that of NaHCO3. There was an increasing heat resistance as the powder concentration increased from 80 g/m3 to 240 g/m3, which blocked the penetration of heat from the flame into the interior of particle cloud and disabled interior particles’ thermal decomposition, leading to a weakening concentration effect.
To investigate the effect of blockage ratios (φ) on the inhibited flame, an experimental study was performed to suppress the methane-air explosions in a 5 L duct with the blockage ratios φ = 0, 0.2, 0.4, 0.6, 0.7, 1.0 under BC and Al(OH)3 inhibitors with the mass concentrations C = 0 g/m3, 80 g/m3, 160 g/m3 and 240 g/m3. The results indicated that the flame fragmentation increased with the improvement of the suppression efficiency. The maximum explosion pressure (pmax) and the deflagration index of the explosion (Kst) were dominated by the combustion rate and the discharge rate. Furthermore, φ = 0.7 was the inflection point of pmax and Kst curves. The drop rate in the Pmax (δ) firstly increased and then decreased as the blockage ratio increased. And the maximum δmax was achieved at the blockage ratio between 0.4 with 0.6. In general, the suppression efficiency of Al(OH)3 and NaHCO3 powders was comparable. However, the low turbulence caused by certain blocking ratios impacted the sedimentation of inhibitor particles, which made the suppression efficiency of Al(OH)3 better than that of NaHCO3. There was an increasing heat resistance as the powder concentration increased from 80 g/m3 to 240 g/m3, which blocked the penetration of heat from the flame into the interior of particle cloud and disabled interior particles’ thermal decomposition, leading to a weakening concentration effect.
2019, 39(11): 115404.
doi: 10.11883/bzycj-2018-0276
Abstract:
Using a 20 L spherical explosive device filled with porous rare earth metal materials, we investigated the explosion characteristics variation of the premixed methane-air mixture in two different filling patterns: spherical and flaky. The influences of blank rate and packed density on the explosion characteristics were considered. And the pressure sensor was used to record the explosion pressure inside the spherical device. It shows that the methane explosion pressure, the maximum pressure rise rate, and the explosion index are all proportional to the blank rate and inversely proportional to the packed density. The drop rate of the maximum explosion pressure of the flaky materials is greater than that of the spherical materials. The explosion suppression performance of the flaky materials is better than that of the spherical materials, and the dual function of the flaky materials has a stronger influence on the explosion power. The main mechanisms of fire and explosion suppression in the two different filling patterns are different.
Using a 20 L spherical explosive device filled with porous rare earth metal materials, we investigated the explosion characteristics variation of the premixed methane-air mixture in two different filling patterns: spherical and flaky. The influences of blank rate and packed density on the explosion characteristics were considered. And the pressure sensor was used to record the explosion pressure inside the spherical device. It shows that the methane explosion pressure, the maximum pressure rise rate, and the explosion index are all proportional to the blank rate and inversely proportional to the packed density. The drop rate of the maximum explosion pressure of the flaky materials is greater than that of the spherical materials. The explosion suppression performance of the flaky materials is better than that of the spherical materials, and the dual function of the flaky materials has a stronger influence on the explosion power. The main mechanisms of fire and explosion suppression in the two different filling patterns are different.
