Fuel-air Explosion Research Articles

Experimental and numerical study on explosion resistance of polyurea-coated shelter in petrochemical industry

To reduce the number of casualties in explosion accidents, blast-resistant shelters can be used to protect personnel in high-risk areas of petrochemical processing plants. In this work, the deformation behaviours of uncoated and polyurea-coated blast-resistant plates were studied through gas explosion tests. An ANSYS/LS-DYNA model of a polyurea-coated shelter was established, and the dynamic responses of the shelter under various explosion loads were analysed. A series of fuel–air explosion tests were carried out to investigate the explosion resistance of the full-scale shelter. The results showed that compared with the uncoated blast-resistant plate, the deformation of the polyurea-coated blast-resistant plate was significantly reduced. The overall deformation of the shelter was the central depression of the wall and the inward bending of the frame. The damage effect of a typical high-overpressure, low-duration load was greater than that of typical low-overpressure, long-duration load. The shelter remained intact under three repeated explosive loads, with cracks appearing on the inner wall but no collapse or debris splashing. The shock wave attenuation rate of the shelter reached over 90%, which could significantly reduce the number of indoor casualties.

Shale gas completion fracturing technology based on FAE controlled burning explosion

The existing fracturing technology in shale gas production lacks compatibility between efficiency and environmental concerns, which significantly hinders the industrial production of shale gas. Therefore, based on the distinctive characteristics of fuel-air explosives (FAE), this paper proposes an advanced shale gas completion fracturing technology utilizing FAE controlled burning explosion, which can effectively achieve a balance between efficiency and environmental considerations. Research and numerical simulations demonstrate that various factors or ways in the FAE burning explosion can exert controllable effects: the higher the zero oxygen equilibrium value and the uniformity of FAE, the greater the initial pressure, and the greater the filling mass of FAE, thereby the stronger the explosion power; the larger inertness coefficient leads to lower sensitivity and intensity of FAE; etc. Additionally, the research and numerical simulation also show that the controllability of FAE burning explosion fracturing on shale reservoirs can be achieved through a variety of factors and ways: an increased explosion pressure results in a larger fracturing zone; the deeper the fractured rock layer leads to higher fracture pressures but a smaller fracturing zone; larger Poisson’s ratio reduces crushed zone while enlarging both crack zone and the fracturing zone.

Optimization of Ejection Characteristics for Twice-Detonating Device in Double-Event Fuel-Air Explosive with High Drop Velocity

The key to ensure the reliability of the cloud detonation in high-drop-velocity double-event fuel-air explosives (DEFAEs) is to cause the twice-detonating device (TDD) to detonate in the dispersed fuel. Here, an ejection mechanism for a TDD is designed and the ejection process is analyzed through an outfield ejection test. Accordingly, a simulation model for the description of the ejection process is established and verified to be reliable by comparing it with the experimental results. Based on the model, two extended ensamples for design optimization of the ejection mechanism are developed. The factors influencing the ejection characteristics of the TDD are further analyzed, including the ejection charge mass and screw (for baffle fixing) parameter. The research carried out here provides theoretical and experimental support for the optimal design of the ejection mechanism in high-drop-velocity DEFAEs.

Dispersal Characteristics Dependence on Mass Ratio for Explosively Driven Dry Powder Particle

An investigation on the dispersal characteristics of the cylindrically packed material of dry powder particles driven by explosive load is presented. By establishing a controllable experimental system under laboratory conditions and combining with near-field simulation, the particle dispersal process is described. Additionally, Kelvin–Helmholtz instability is observed during the process of jet deceleration dispersal. The characteristic parameters of radially propagated particles are explored under different mass ratio of particle-to-charge (M/C). Results indicate that, when the charge mass remains constant, an increase in M/C leads to a decrease in dispersed jet number, void radius and maximum velocity, wherein the maximum velocity correlates with calculations by the porous Gurney model. The case of the smaller M/C always has a higher outer-boundary radius and area expansion factor. Findings indicate that when particles detach from the jet upon reaching minimum acceleration and entering low-speed far-field stage from high-speed near-field stage, the outer-boundary radius is 30~36 times the initial particles’ body radius under different M/C. In addition, particle concentration distribution over time and distance is qualitatively analyzed by the grayscale image method. This research can be referential for improving the fire-extinguishing capacity of extinguishing bombs and the damage property of fuel air explosive (FAE).

Detangling the detonation of combustible clouds

Numerical models simulate how clouds of fuel-air explosives form and detonate.

Study on concentration distribution and detonation characteristics for non-axisymmetric fuel dispersal

The study of non-axisymmetric fuel dispersal and detonation can provide reference for the prevention of industrial cloud explosion accidents and the design of fuel air explosive (FAE). The concentration and detonation fields of 85 kg cylindrical and fan-shaped fuel are investigated by experiments and numerical simulations. A dynamic model of the whole process for fuel dispersal and detonation is built. The concentration distribution of fuel is used as the initial condition to calculate the detonation stage, thus solving the initial value problem of detonation field. The phase and component changes of fuel cloud at different locations are compared. The fuel cloud is divided into directions of 0°, 90°, 135° and 180°. The results show that the maximum cloud radius is 20.94 m in 135° and the minimum is 12.04 m in 0°. The diameter of the detonation fireball is 53.6 m, and the peak temperature is 3455 K. The highest peak overpressure is 3.44 MPa in 0° and the lowest is 2.97 MPa in 135°. The proportion of liquid phase in 0° is 22.90%, and the fuel loss is 11.8% and 9% higher than that in 135° and cylindrical charge, respectively. The stable propagation distance of blast wave in 135° is 42.50% longer than 0° and 28.37% longer than cylindrical charge.

Explosion behaviors of vapor–liquid propylene oxide/air mixture under high-temperature source ignition

Propylene oxide (PO) is widely used in fuel–air explosive (FAE) and pulse detonation engines (PDE). The explosion process of PO/air mixture in a 20 L spherical container under high-temperature source ignition was studied through experiment and numerical simulation. A good agreement was observed between the experimental and simulation results. The ignition temperature (1100–2500 K) and initial droplet size (10–200 μm) had no obvious effect on the maximum explosion pressure (Pmax) at a nominal concentration of 130 g/m3. Explosion time (te) and reaction time (tr) of PO aerosol explosion increased with the increase in initial droplet size. The flame propagation process in the direction of 90° was not the same as that of 45°. Explosion flame propagated from the center to the surrounding area, then sagged along wall facing the center and presented a U-shape. Explosion time at ignition temperature of 1600 K was 29.63 ms, which was the shortest compared with the temperature of 2000 K, 2500 K, and 1100 K. The influence of ignition temperature on te was more obvious than that of initial droplet size. The flame propagation mechanism of droplet sizes of 10 μm and 50 μm was different from that of 100 μm and 200 μm. The time to reach the maximum flame temperature(tf) increased with the increase in droplet size; the flame propagation speed decreased with the increasing droplet size, and the maximum flame velocity can reach 6.07 m/s.

Flame behavior, shock wave, and instantaneous thermal field generated by unconfined vapor-liquid propylene oxide/air cloud detonation

Energy output and heating effects are essential for vapor-liquid fuel/air cloud detonation in the fuel-air explosive (FAE) applications or explosion accidents. The purpose of this study is to examine the dynamic large-size flame behavior, shock wave propagation law, and instantaneous thermal field generated by unconfined vapor-liquid propylene oxide (PO)/air cloud detonation. Based on computational fluid dynamics (CFD) and combustion theory, a numerical simulation is used to study the detonation process of a PO/air cloud produced by a double-event fuel-air explosive (DEFAE) of 2.16 kg. The large-scale flame behavior is characterized. The flame initially spreads radially and laterally in a wing shape. Subsequently, the developed flame increases with a larger aspect ratio. Moreover, the propagation laws of shock waves at different heights are discussed. The peak pressure of 1.3 m height level with a stepwise decline is obviously different from that of the ground with an amplitude of reversed 'N' shape. In the vast majority of the first 6.9 m, the destructive effect of the shock wave near the ground is greater than that of the shock wave at 1.3 m height. Furthermore, the dynamic instantaneous isothermal field is demonstrated. The scaling relationship of various isotherms in the instantaneous thermal field with the flame and initial cloud is summarized. The comprehensive numerical model used in this study can be applied to determine the overpressure and temperature distribution in the entire fuel/air cloud detonation field, providing guidance for assessing the extent of damage caused by DEFAE detonation.

Effects of gas concentration and obstacle location on overpressure and flame propagation characteristics of hydrocarbon fuel-air explosion in a semi-confined pipe

Experiments were conducted in a semi-confined pipe to investigate the effects of obstacle location and gasoline vapor concentration on gasoline-air fuel explosions. The variations of internal overpressure, external overpressure, flame propagation and flame-overpressure coupling relationship were analyzed. The results showed that the internal overpressure histories existed three obvious peaks, and when the obstacle location was set at 0.4 m, the maximum absolute values of overpressure (pmax and pneg), overpressure rise rates ((dp/dt)ave and (dp/dt)max) and the deflagration index (KG) were obtained. Additionally, more than two positive overpressure peaks were observed in the external overpressure histories. The maximum values of external overpressures and overpressure rise rates were obtained at the obstacle location of 0.4 m. For the fuel concentrations of 1.3%, 1.7% and 2.1%, the shortest time to reach pmax appeared at the obstacle location of 0.4 m, 0.2 m and 0.6 m, respectively, while the shortest time to reach (dp/dt)max and the maximum flame propagation speed were obtained for all the fuel concentrations at the obstacle location of 0.2 m. Moreover, a coupling relationship between overpressure and flame propagation was found. It could be deduced that the formation of the positive overpressure peak of the external overpressure might be directly related to the gas explosion inside the pipe and the flow jet caused by the high-speed flame propagation, rather than the external explosion (or secondary explosion) out of the pipe. These results improve our understanding on gas explosion dynamics in a semi-confined space.

Effect of metal powders on explosion of fuel-air explosives with delayed secondary igniters

In order to improve the energy level of fuel air explosive(FAE) with delayed secondary igniters, high energetic metal powders were added to liquid fuels mainly composed of ether and isopropyl nitrate. Metal powders’ explosive properties and reaction mechanisms in FAE were studied by high-speed video, pressure test system, and infrared thermal imager. The results show that compared with pure liquid fuels, the shock wave overpressure, maximum surface fireball temperature and high temperature duration of the mixture were significantly increased after adding high energetic metal powder. The overpressure values of the liquid-solid mixture at all measuring points were higher than that of the pure liquid fuels. And the maximum temperature of the fireball was up to 1700 °C, which was higher than that of the pure liquid fuels. After replacing 30% of aluminum powder with boron or magnesium hydride, the shock wave pressure of the mixture was further increased. The high heat of combustion of boron and the hydrogen released by magnesium hydride could effectively increase the blast effect of the mixture. The improvement of the explosion performance of boron was better than magnesium hydride. It shows that adding high energetic metal powder to liquid fuels can effectively improve the explosion performance of FAE.

Research on explosive dust space ventilation scheme based on CFD simulation

Aluminum powder with high explosive sensitivity, strong detonation performance and low price has become the first choice fuel for fuel air explosives. Design three types of exhaust schemes for specific powder operation spaces, and use CFD simulation technology to study the flow field and dust removal characteristics of the three schemes. The results show that the bottom ventilation scheme has the best dust removal effect, the characteristic time of dust removal is 9.4s, and the maximum dust concentration is 85g/m3. And the characteristic flow field range of the bottom exhaust scheme is the smallest (4.12m×3.05m), which indicates bottom scheme has the least disturbance to the spatial flow field, so this scheme should be selected for ventilation and dust removal design. In addition, the function relationship between the wind pressure and the characteristic dust removal time is obtained by setting different wind pressures, which provides a basis for the design of the graded ventilation dust removal side according to the design.

Establishment and analysis of damage calculation model under fuel air explosion effect

Fuel air explosive has unique damage characteristics because of its different action mechanism. In this paper, through analyzing the damage mechanism and characteristics of fuel air explosive, the damage efficiency of fuel air explosive was quantitatively described by using overpressure and specific impulse. In combination with theoretical calculation and experimental fitting, the corresponding damage effectiveness calculation model of fuel air explosive was established. According to the actual application of fuel air explosive, the group of personnel was selected as the pseudomorphic target, the distribution area and relevant parameters of the target were set, so as to establish the corresponding damage criteria, which provided a reference for the effective evaluation of the damage efficiency of fuel air explosive.

ОСОБЛИВОСТІ ФУНКЦІОНУВАННЯ ТА РОЗРОБКИ ТЕРМОБАРИЧНИХ БОЄПРИПАСІВ

У статті акцентовано увагу на особливості функціонування термобаричних вибухових речовин. Показано основні переваги та недоліки термобаричних вибухових речовин різних поколінь. Проведено оцінку стадій вибух термобаричних зарядів. Проаналізовано характер навантаження при оцінці уражаючої дії термобаричних вибухових речовин. Визначено, що характер навантаження пов'язаний зі співвідношенням тривалості фази стискання в ударній хвилі та періоду власних коливань об'єкта.

Effects of concentration, temperature, ignition energy and relative humidity on the overpressure transients of fuel-air explosion in a medium-scale fuel tank

Experiments were conducted in a 907.5-L fuel tank to investigate the effects of concentration, temperature, ignition energy, and humidity on the explosion overpressure transients of gasoline-air mixture explosions. The results show that the overpressure-time profiles can be roughly divided into four stages: incubation stage, slow acceleration stage, abrupt acceleration stage, descending stage. During the explosion process, intense overpressure oscillation occurred in the fuel tank. Specifically, both the maximum overpressure (pmax) and the maximum rate of overpressure rise ((dp/dt)max) increased firstly and then decreased as the gasoline concentration increased, and the correction between overpressure parameters and gasoline concentration is approximately cubic polynomial. The peak values of pmax and (dp/dt)max were obtained at the concentration of 1.71%.The influence of temperature on pmax and (dp/dt)max was relatively complex, which may result from the vessel volume and the initial gas concentration. Moreover, with the increase of ignition energy, pmax and (dp/dt)max according to a linear increase trend and a logarithmical increase trend, respectively. With the increase of initial humidity, both pmax and (dp/dt)max showed a linear decrease trend. These results are useful for understanding the explosion characteristics of fuel-air mixtures under various initial conditions in medium-scale fuel tanks.

Comparison of detonation characteristics in energy output of gaseous JP-10 and propylene oxide in air

Propylene oxide (PO) is a traditional fuel in fuel–air explosives (FAE), and exo-tetrahydrodicyclopentadiene (JP-10) is a newly developed aviation fuel with a high volumetric energy density. Detonation properties of gaseous JP-10 and PO in a confined cylindrical tube were studied by two-dimensional simulation. Results show that the magnitude, trend and law of change in detonation properties of JP-10/air are similar to those of PO/air. Firstly, JP-10 achieves superior detonation properties to PO under the same volumetric fraction rather than under the same mass. However, by comparison of the two fuels, JP-10 achieves the same detonation effect at lower concentrations and saves up to 61.6% of fuel mass than PO. In addition, the length of post-shock high-temperature-and-pressure zone in PO/air is greater than that of JP-10/air, which is advantageous to improve the power capacity and damage ability. It is also noteworthy that PO has a shorter chemical reaction time than JP-10, which makes it easier to support self-sustaining detonation propagation by a short period of chemical exothermic process. This work could be of great significance to investigate the dispersing and detonation performances of JP-10 and PO in applications of FAE, and facilitate the optimization of FAE components.

Research on FAE Cloud Image Processing Method Based on Background Subtraction and Region Growing

After the first initiation, the Fuel Air Explosive (FAE) cloud formed through fuel explosion dispersal and it will generate tremendous damaging power after being detonated the second time. As the damaging power is closely related to the determination of reinitiation time, it is of great significance to study the growth principle of FAE cloud by means of analyzing FAE cloud images. Combining with background subtraction and region growing, an improved region growing image processing method was proposed, in which the seeds of region growing abstracted through background subtraction method and the growing criterion was modified. With this method, the integrate area of cloud can be obtained for extracting geometric parameters. Experiments were carried out on both cloudy and sunny days, and image overlap score was used to quantitatively evaluate the accuracy of images segmentation. The result indicated that this image processing method has advantages of high precision and robustness. In addition, the computation burden is reduced significantly compared with traditional region growing method.

Influencing Factors of the Initiation Point in the Parachute-Bomb Dynamic Detonation System

The parachute system has been widely applied in modern armament design, especially for the fuel-air explosives. Because detonation of fuel-air explosives occurs during flight, it is necessary to investigate the influences of the initiation point to ensure successful dynamic detonation. In fact, the initiating position exist the falling area in the fuels, due to the error of influencing factors. In this paper, the major influencing factors of initiation point were explored with airdrop and the regularity between initiation point area and factors were obtained. Based on the regularity, the volume equation of initiation point area was established to predict the range of initiation point in the fuel. The analysis results showed that the initiation point appeared area, scattered on account of the error of attitude angle, secondary initiation charge velocity, and delay time. The attitude angle was the major influencing factors on a horizontal axis. On the contrary, secondary initiation charge velocity and delay time were the major influencing factors on a horizontal axis. Overall, the geometries of initiation point area were sector coupled with the errors of the attitude angle, secondary initiation charge velocity, and delay time.

Study on the thermal behaviors of nano-Al based fuel air explosive

The thermal behaviors and mechanism of nano-based fuel air explosive (FAE) were investigated by using DSC measurements in different situations and DSC/TG–FTIR–MS coupled technique. The thermal decomposition process of FAE under non-oxidizing environment was analyzed and described. The decomposition of FAE takes place in a multistage complex process. The first process is assigned to volatilization process of the volatile components. With an increase in temperature, isopropyl nitrate starts to break up into alkene and secondary alcohol. In the temperature range of 350–500 °C, the dominant volatile products are hydrocarbon fragments, CO2 and H2O. At the same time, the full formulation of FAE and formulation without nano-Al powder were studied and compared. The thermal decomposition of other components in FAE is significantly promoted by nano-Al powder.

An experimental study on vapor cloud explosion of propane-oxygen stoichiometric mixture

Vapor cloud explosions (VCEs) are serious hazards in refining and petrochemical industries. Statistics indicate that 75% of the total losses were caused by explosion so that considerable research effort has been focused on this subject. Consequences of an explosion are aerial overpressure and impulse, responsible for injury to humans and structures. Many studies were performed with fuel-air explosions but few works focused on fuel-oxygen mixtures explosion. In this study, experiments were performed on a large experimental field. In order to represent realistic conditions, the shape of the gas envelope was elongated like the dispersion shape from leakage with small wind. The flammable cloud was ignited with SEMTEX explosive charges put at the center of the gas volume envelopes. Overpressure values were collected at different positions on the field. Flame propagation was recorded by high speed camera and gave a constant velocity of 2384 m.s-1 , indicating a detonation regime.

Ignition and Combustion Characterization of Nano-Al-AP and Nano-Al-CuO-AP Micro-sized Composites Produced by Electrospray Technique

Metal powders such as aluminum nanoparticles (Al NPs) have been found huge potential as reactive additives to highly increase energy density in various energetic systems such as propellants, explosives and pyrotechnics. However, it is suffering issues of agglomeration and post-combustion aggregates, which largely reduce the energy utilization efficiency and the energy release rate. One option to eliminate this disadvantage is to coat the nanoparticles with gas generator which can produce gas to prevent the sintering. This work use electrospray technique to assemble Al NPs and Al-CuO NPs into microparticles, with coating of gas generator-ammonium perchlorate (AP) to produce gas to prevent possible sintering, thus obtaining a highly reactive Al-based composites. The Al/CuO NPs composites are ignited in a confined cell to measure its combustion pressure history. The peak pressure and the pressurization rate of Al/CuO/AP is more than 3X higher and faster, compared to the physically mixed Al/CuO nanothermite. This work provides an ideal approach to prepare Al NPs based energetic materials such as solid propellant or solid fuel air explosives.