Search

The effect of an extension tube with a rectangular slit inlet on the opening status of the metal diaphragm, as well as spontaneous ignition of pressurized hydrogen are experimentally investigated. The results show that the opening ratio of the metal diaphragm exhibits a positive correlation with the increase of the slit area. It also shows an initial increase followed by a decrease as the failure pressure rises. Moreover, the shock overpressure and Mach number inside the tube with the slit entrance are significantly reduced compared to those within the circular inlet tube. The critical pressure for spontaneous ignition in the tube with narrow inlet is notably affected by the slit parameters, increasing progressively with decreasing slit area and slightly increasing with raising slit aspect ratio. These experimental results would serve as valuable references for further exploring the failure modes of hydrogen storage containers and mechanisms underlying the spontaneous ignition. • The opening ratio of partially ruptured burst disks is statistically measured. • The slit inlet attenuates the overpressure but does not modify its axial trend. • The abnormal rupture of diaphragm leads to the compression waves preceding shock. • The threshold exceeded opening ratio is not the main determinant of self-ignition. [ABSTRACT FROM AUTHOR]

Due to the high probability of hydrogen leaking from narrow cracks of the vessels, an experimental study is conducted to investigate the spontaneous ignition of high-pressure hydrogen released into a tube through inlets with different narrowness, including circular, square (length-width ratio χ = 1), and two slit shapes of χ = 2 and 3, with the same area. Pressure transducers and photoelectric sensors are used to detect shock wave dynamic variation and ignition occurrence. The results indicate that narrow inlets weaken the shock wave intensity and speed, and the weakening effect increases with narrowness. Moreover, spontaneous ignition is affected. The minimum burst pressure required for spontaneous ignition is higher in the cases with square and slit inlets. Most significantly, when χ is 3 , it is 2.5 times that of circular inlet. Meanwhile, for narrow inlets, the ignition flame intensity and speed are enhanced, and the inlet of χ = 2 has the greatest impact. • The influence of narrow releasing ports on self-ignition hydrogen is investigated. • Narrow ports weaken the shock wave intensity and speed. • It requires higher burst pressure for self-ignition under narrow ports. • The flame intensity is enhanced under narrow ports. • Different narrowness of the ports brings different effects. [ABSTRACT FROM AUTHOR]

A medium-scale model (1/10) of an underground parking garage is designed and built to study the characteristics of the release and dispersion of hydrogen leaked from hydrogen fuel cell vehicles (HFCVs) in underground garages. Helium is used in place of hydrogen for safety reasons. The helium release experiments are conducted and the variations in helium concentrations at different locations and times in the garage model are obtained. The influence mechanisms of the leakage flow rate and nozzle diameter on the spatial and temporal distributions of the helium concentration are revealed. The experimental results show that the initial release rate of helium is the key factor affecting the distribution of helium concentrations. Both leakage flow rate and nozzle diameter have a significant influence on helium concentrations by affecting the initial release rate. If the release time is long enough, the helium concentrations will experience three stages during release, namely, rapid growth, slow growth and relatively stable. Furthermore, the beams of the garage can reduce the area on the ceiling where the hydrogen concentration exceeds the lower flammable limit (LFL). On the other hand, the beams can make it easier for local hydrogen concentrations to reach the LFL. This work can provide theoretical support for the design and construction of underground parking garages and the arrangement of hydrogen detectors. • The helium dispersion in an underground parking garage is experimentally investigated. • The helium concentration on the ceiling above the car is not always the highest. • Variations in helium concentration go through three stages. • The beam can reduce the dangerous area but increase the local helium concentration. • Both a large leakage flow rate and a large nozzle diameter can lead to a higher helium concentration near the ceiling. [ABSTRACT FROM AUTHOR]

To address the actual disaster of thermal decomposition and explosion of ammonium nitrate (AN), a commonly used raw material, urea was selected as an additive to study its effect on the thermal decomposition of AN through experimental and theoretical methods. The thermal decomposition kinetics, energy release, self-reaction properties of adiabatic environments, and escaping gaseous products have all been discussed. It was found that urea has an inhibitory effect on the crystalline transformation of AN stored at room temperature, which is beneficial to its thermal safety. The results showed that urea increased the activation energy of the thermal decomposition of AN, raised the temperature of the initial reaction and reduced heat generation. Furthermore, the action mechanism of urea is suggested to be heat absorption by its thermal decomposition and the escape of ammonia. Finally, the study carried out an engineering assessment of the thermal safety of AN under the action of urea and found that the addition of urea greatly enhanced the thermal safety performance of stored and transported AN. The comprehensive analysis concluded that a small dose of urea could be added to enhance the thermal stability of AN without affecting its normal function. [Display omitted] • The effect of urea on the pyrolysis of AN is systematically analyzed. • Urea boosts the activation energy of the thermal decomposition reaction. • Urea reduces the heat of reaction and delays characteristic gas generation. • Urea increases the safety of adiabatic conditions for AN. • Urea improves the safety of large-scale stacking of AN. [ABSTRACT FROM AUTHOR]

Complete and efficient delamination of cathode foil is a pivotal precondition for spent lithium-ion battery (LIB) recycling, determining the realizability of the subsequent operational processes. Current methods are based on the decomposition or dissolution of the polyvinylidene fluoride (PVDF) binder, which eliminates the adhesion between the components and thus results in separation. In this work, the analysis of solubility parameters has inspired the successful application of a green solvent, γ-valerolactone (GVL), for PVDF dissolution and was further utilised to delaminate spent cathode foils for direct recycling. Complete delamination of spent cathode foils was successfully achieved in GVL at 80 °C with 600 rpm stirring, and an ultrasound-assisted strategy was proposed to further improve the separation efficiency. The optimised conditions were determined by orthogonal experiments, with excellent delamination efficiency (99.2%) in the ultrasound-assisted GVL delamination process. Herein, a closed-loop recovery process has been proposed to completely reclaim cathode active materials, Al foil, carbon black, and PVDF binder from spent LIBs without complex treatments. Finally, a tentative exploration of possible delamination mechanisms has been discussed. Economic and environmental analyses based on the EverBatt model confirm the feasibility of its practical applications. This study provides an environmentally benign, highly safe, and sustainable pathway for recycling spent LIBs. [ABSTRACT FROM AUTHOR]

Experiments on shock waves propagation, spontaneous ignition, and flame development during high-pressure hydrogen release through tubes with symmetrical obstacles (O 1-1) and asymmetrical obstacles (O 1-2) are conducted. The obstacle's side is triangular with a length of 4 mm, a height of 3.6 mm, and its width is 15 mm. In the experiments, a reflected shock wave generates and propagates both upstream and downstream when the leading shock wave encounters the obstacle. At the same burst pressure, the reflected shock wave intensity in tube O 1-1 is significantly greater than that in tube O 1-2. Moreover, the presence of obstacles in the tube can induce spontaneous ignition. The minimum burst pressures for spontaneous ignition for tubes O 1-1 and O 1-2 are 2.84 MPa and 3.28 MPa respectively, lower than that for the smooth tube. Furthermore, both the initial ignition position and ignition time are greatly advanced in obstruction tubes, mainly affected by obstacle positions and burst pressures. Finally, the flame separation process near the obstacle is observed. After passing the obstacle, the flames grow rapidly in radial and axial directions on the tube sidewalls. And at the same burst pressure, the flame convergence time in tube O 1-2 is usually longer than that in tube O 1-1. • The influence of obstacles arrangements on self-ignition hydrogen is investigated. • Reflected shock wave forms and propagates both upstream and downstream. • The presence of the obstacles can facilitate the occurrence of self-ignition. • Obstacles arrangements have great effects on ignition positions and ignition time. • The flame separation is observed inside both obstruction tubes. [ABSTRACT FROM AUTHOR]

The dynamic mechanisms of self-ignition and flame propagation during high-pressure hydrogen release through a rectangular tube were experimentally investigated using pressure records, flame detection and high-speed photographs. Experimental results show that the minimum burst pressure for self-ignition decreases with an increase in axial distance to the diaphragm and then remains at an almost constant value. The self-ignition onset at the same location of the tube exhibits a certain randomness even if the intensity of the shock wave produced in the tube is similar. Multiple ignitions were observed at the early stage of hydrogen release. They usually had difficulty to sustainably develop and were extinguished owing to oxygen deficiency. At a subsequent stage, the ignition kernel appears again and grows rapidly in the axial and radial directions, finally converging to a complete flame across the tube width. It was found that the radial growth rate of the flame was lower than the axial growth rate. [ABSTRACT FROM AUTHOR]

[Display omitted] The depletion of fossil fuels has led to the rapid development of environmentally friendly lithium ion battery (LIB). However, exposure of LIB to elevated temperatures frequently leads to battery failure, thermal runaway (TR), or even TR propagation. In this study, a series of experiments are conducted on the LIBs with and without water mist at different initial temperatures (50 °C and 106–206 °C) in a novel designed battery module to investigate the cooling effect of water mist. The results show that water mist reduces the possibility of battery failure and inhibits TR. The critical temperature of TR is enhanced by 36 °C. Moreover, using water mist to suppress the TR propagation requires reducing the temperature of a cell that undergoing TR to below 126 °C. Analysis of cooling rate indicates that there are four cooling modes ((Ⅰ) rapid cooling and quasi-steady state, (Ⅱ) rapid cooling and slow cooling, (Ⅲ) transitional stage, and (Ⅳ) rapid heating and rapid cooling) of water mist. The heat absorbed by water mist is distinct in four cooling modes. These results reveal that water mist has better cooling effect and the cooling mode changes with the increase of temperature, which may provide insight into the thermal safety performance of cells. [ABSTRACT FROM AUTHOR]

• The influence of a sho (ϸ)-shaped tube on the spontaneous ignition is investigated. • There are complex shock wave interactions in the bend section. • Spontaneous ignition is more prone to occur in the bend section. • The flame in the bend section cannot spread to the straight section. • There are two jet fires with a long-time interval outside the sho-shaped tube. The geometry of the extension tube has a great influence on the shock wave propagation and spontaneous ignition of high-pressure hydrogen release in this paper, piezoelectric pressure transducers, photodiodes and a high-speed camera are used to study the shock wave propagation and spontaneous ignition of high-pressure hydrogen released to the downstream sho (ϸ)-shaped extension tube. Experimental results show that the intensity of the leading shock wave is weakened due to the presence of branches when it propagates in the straight section of the sho-shaped tube, and a strong reflected shock wave is generated in the bend section. Spontaneous ignition is more prone to occur in the bend section than in the straight section, with a large optical signal value and long flame duration. However, due to the complex structure of the extension tube, there are still cases of the hydrogen flame extinguishing inside the tube even under high burst pressure. The flame detection time after the leading shock wave at the measured positions decreases with increasing burst pressure, and the time in the bend section is greater than that of the straight section. Radial flame expansion, flame separation, downstream flame extinction and upstream flame development, primary jet fire and secondary jet fire are successively observed outside the tube. [ABSTRACT FROM AUTHOR]

This paper demonstrates experimental investigation on the self-ignition and subsequent flame propagation of high-pressure hydrogen-methane mixture release via a tube. The proportion of methane added to hydrogen is 2.5% (vol.). A transparent rectangular tube (d = 15 mm, L = 400 mm) is used in the experiments. It is shown that the minimum burst pressure required for self-ignition increases 1.57 times for only 2.5% methane addition from 2.89 MPa (pure hydrogen) up to 4.68 MPa (2.5% CH 4 addition). This is mainly caused by the following reasons: on the one hand, methane addition can result in the decease of shock intensity inside the tube, thereby lowering the temperature of the combustible mixture; on the other hand, the hydrogen-methane mixture has the higher minimum ignition energy than that of pure hydrogen. Besides, 2.5% methane addition can increase the initial ignition time, weaken the flame intensity and reduce the flame propagation velocity relative to tube wall inside the tube. Moreover, for cases with 2.5% methane addition, the complete flame throughout the tube is formed closer to the back end of the tube. When the self-sustained flame exits from the tube, the maximum overpressure in a confined space increases with 2.5% methane addition. • The effect of 2.5% methane addition to hydrogen is experimentally investigated. • The shock wave intensity is reduced in the presence of the methane. • The addition of methane can decrease the possibility of hydrogen self-ignition. • Initial ignition occurs in the tube wall and then develops into a complete flame. • The hydrogen-methane mixture brings greater combustion overpressure in chamber. [ABSTRACT FROM AUTHOR]

• Critical failure condition for various installations facades were investigated. • Thermal-mechanical model was developed to calculate temperature and stress field. • Optimization simulation was conducted to obtain a better thermal resistance. The extensive application of various types of point-supported glass facades may bring potential thermal breakage risk and impacts on indoor human beings safety. In this work, point-supported glass facades with five various types were tested under thermal loads. The present results showed that installation forms influenced significantly the first breaking time, the location of crack initiation and the final falling out area. It demonstrated that the one-point-supported glass facades had the longest time for the first crack occurrence whereas the glass eventually fell completely out of the frame. However, the six-point-supported glass facades had the shortest first breaking time, but ultimately no glass pieces fell out of the frame. To calculate the temperature variation and stress distribution of glass panel, a thermal-mechanical model was developed. In addition, an optimization simulation was further conducted using the bound optimization by quadratic approximation method to obtain a better thermal resistance performance of glass facade. This work provides significant insights on the effects of various installations upon the thermal response of glass facades and helps to understand the failure mechanism and build safer facades by the structural optimization method. [ABSTRACT FROM AUTHOR]

The shock wave dynamics, spontaneous ignition and flame variation during high-pressure hydrogen release through tubes with different cross-section shapes are experimentally studied. Tubes with square, pentagon and circular cross-section shapes are considered in the experiments. The experimental results show that the cross-section shape of the tube has no great difference on the minimum burst pressure for spontaneous ignition in our tests. In the three tubes with length of 300 mm, spontaneous ignition may occur when overpressure of shock wave is 0.9 MPa. When the spontaneous ignition is induced in a non-circular cross-section tube, the possible turbulent flow in the corner of the tube increases can promote the mixing of hydrogen and air, thus producing more amount of the hydrogen/air mixture. As a result, both the peak light signal and flame duration detected in the non-circular cross-section tubes are more intense than those in the circular tube. The smaller angle of the corner leads to a more intensity flame inside tube. When the hydrogen flame propagates to the tube exit from the circular tube, the ball-like flame developed near tube exit is relatively weak. In addition, second flame separation outside the tube is observed for the cases of non-circular cross-section tubes. • The effect of cross-section shapes of tube has been experimentally investigated. • The use of burst disk with cross notching on surface exhibits good repeatability. • The ignition occurs when the overpressure of shock wave is about 0.9 MPa. • The cross-section shape shows a significant influence on the flame intensity. • Twice flame separation are observed for cases of non-circular cross-section tubes. [ABSTRACT FROM AUTHOR]

An experimental study of shock wave propagation and its influence on the spontaneous ignition during high-pressure hydrogen release through a tube are measured by pressure transducers and light sensors. Results show that the pressure behind a shock wave first increases, and subsequently remains near constant value with an increase of the propagation distance. That is, a certain propagation distance is required to form a stable shock wave in the tube. In the front of the tube, the minimum value of pressure behind the shock wave (P shock) required for spontaneous ignition decreases with the increase in axial distance to the diaphragm. However, the minimum P shock remains nearly a constant value in the rear part of the tube. Moreover, the critical values of shock Mach number (M S) for spontaneous ignition decrease with the increase in tube length. And the ignition delay time decreases with the increase of the M S. As the ignition kernel grows in size to a flame, it propagates downstream along the tube with velocity greater than the theoretical flow velocity of the hydrogen-air contact surface. The flame propagation velocity relative to tube wall increases with M S. When the self-sustained flame exits from the tube, a rapid non-premixed turbulent combustion is observed in the chamber. The combustion-wave overpressure increases with the increase of the M S. • The influence of shock wave intensity on spontaneous ignition is investigated. • A certain propagation distance is required to form a stable shock wave in the tube. • The minimum P shock for self-ignition decreases with increasing the axial location. • The critical shock Mach number for self-ignition decreases with the tube length. • Flame propagation velocity relative to tube wall increases with shock Mach number. [ABSTRACT FROM AUTHOR]

• Thermal runaway and its propagation in lithium-ion battery modules are investigated. • Thermodynamics parameters at different charge levels are obtained. • The dramatic combustion phenomenon in the fully charged module is discovered. • The propagation time to the next battery are 87 s and 307 s for the fully charged and half charged module. Thermal runaway (TR) and its propagation behavior in the large format lithium-ion battery (LIB) with various states of charge (SOC) are experimentally investigated in this work. Thermal runaway feature of the cell under thermal abuse condition is characterized using extended volume accelerating rate calorimeter. Based on the experimental results, the modules with five LIBs are built to analyze TR propagation mechanism and further discuss the impact of SOC on TR propagation behavior. It is found that the TR is firstly triggered on the layer near the front surface of the LIB, and then spread to the whole battery. The average propagation time inside the single LIB is 10 s in the module with 100% SOC while 39 s in the module with 50% SOC. Moreover, the module with 100% SOC shows intense combustion behavior, which is replaced by a considerable amount of smoke in the module with 50% SOC. Besides, the average propagation time between adjacent LIBs is significantly delayed from 87 s in 100% SOC module to 307 s in 50% SOC module. This work details TR propagation feature in large format LIB pack, and can provide the guidelines for the safety design of lithium-ion battery module. [ABSTRACT FROM AUTHOR]

Highlights • Similitude analysis used to derive correlation for hydrogen spontaneous ignition. • The correlation is validated against tests performed in this and other studies. • Burst disks of nickel, aluminum, copper, brass of 0.13–0.4 mm thicknesses are used. • Tubes of 5–20 mm diameter, 80–360 mm length at burst pressure 2–10 MPa are used. • The correlation can be used as a tool for hydrogen safety engineering. Abstract Hydrogen is an emerging energy carrier for green hydrogen and fuel cell vehicles. The compressed gaseous hydrogen is selected by car manufacturers as a preferred option for onboard storage. One possible accident scenario is release of high-pressure hydrogen to the atmosphere through piping and tubes. The spontaneous ignition of accidently released hydrogen can be accompanied by pressure and thermal effects on humans and facilities. However, despite several previous studies, the critical conditions for spontaneous ignition to take place are not yet defined for an arbitrary case. Most of earlier studies present only a qualitative interdependence between the critical burst pressure for ignition and the ignition influencing factors, i.e. tube length and diameter, burst disk opening time, etc. The quantitative correlation is not yet available to underpin inherently safer engineering design of hydrogen systems and infrastructure. This paper focuses on quantitative analysis of the phenomenon of spontaneous ignition during high-pressure hydrogen release through a tube filled with air into the atmosphere. Similitude analysis of the problem is carried out. It is found that the ratio of shock pressure inside the tube to the atmospheric pressure, P s /P a , is a function of the dimensionless parameter, which is the product of the initial storage to the atmospheric pressure ratio, P b /P a , and the ratio of the characteristic shock propagation time to the burst disk opening time, (D/u s)/t. Pressure transducers and light sensors are used in the experiments to record the shock propagation and ignition time and location. The correlation to quantitatively define the critical conditions for spontaneous ignition of released hydrogen inside a tube with air is derived for the first time using the similitude analysis. The correlation is calibrated against experiments carried out in this study and by other authors, where four identical triangular petals are formed upon rupture of inertial burst disk made of metal. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen is expected to be an alternative energy carrier in the future. High-pressure hydrogen storage option is considered as the best choice. However, spontaneous ignition tends to occur if hydrogen is suddenly released from a high-pressure tank into a tube. In order to improve the safety of hydrogen application, an experimental investigation on effects of CO 2 additions (5%, 10% and 15% volume concentration) on the spontaneous ignition of high-pressure hydrogen during its sudden expansion inside the tube has been conducted. Pressure transducers are used to record the pressure variation and light sensors are employed to detect the possible spontaneous ignition. It is found that the shock wave overpressure and the mean shock wave speed are almost the same inside the tube for different CO 2 additions under the close burst pressures. For cases with more CO 2 additions, the ignition detected time is longer and the average speed of the flame, the maximum value of light signals and the detected duration time of spontaneous ignition are smaller. It is shown that minimum burst pressure required for spontaneous ignition increase 1.47 times for 15% CO 2 additions. The minimum burst pressure required for spontaneous ignition increases from 4.37 MPa (0% CO 2) up to 6.41 MPa (15% CO 2). With the increasing of CO 2 additions, it requires longer distance and longer time for hydrogen and oxygen to mix and thus longer ignition delay distance/time. The results showed that additions of CO 2 to air have a good suppressing effect on hydrogen spontaneous ignition. Highlights • Effect of CO 2 doping to air on the spontaneous ignition occurrence is investigated experimentally. • Minimum burst pressure required for spontaneous ignition increases with the increasing of CO 2 addition. • Minimum burst pressure required for spontaneous ignition increase 1.47 times for 15% CO2 additions. • It requires a longer distance and a longer time for spontaneous ignition to take place if more CO 2 is added. [ABSTRACT FROM AUTHOR]

The effect of inorganic additive flame retardant on fire hazard of polyurethane exterior insulation material was experimentally investigated by the cone calorimeter (Cone) and thermal gravimetric-differential thermal analysis. The aluminum trihydrate (ATH) and magnesium hydroxide (MDH) were considered as the inorganic additive flame retardants in the experiments. The results indicated that compared to pure rigid polyurethane foam (RPUF), the RPUF containing inorganic flame retardant could significantly enhance fire resistance and thermal stability. Especially for RPUF, the ratio of MDH and ATH was 1:3, the ignition delay time was extended for about 14.33 s as well as the values of peak heat release rate and the total heat release were reduced by about 50.79 kW m−2 and 2.60 MJ m−2. Also, the peak values of the carbon monoxide release rate were decreased to 0.0096 g s−1. Further, the decomposition process of the RPUFs in nitrogen and air was compared and analyzed. It was found that they could be divided into two stages and three stages, respectively, and small fluctuations of the second stage in air were corresponded to the decomposition of ATH and MDH. Besides, the compressive properties were proved to decrease with the increased additive amount of the metal hydroxides. Based on the experimental results and the classic dynamics methods, the activation energy (Eα) and the pre-exponential factor (A) were obtained and it turned out that the addition of inorganic flame retardant could enlarge the values of Eα and A, which helped to reduce the fire hazard. [ABSTRACT FROM AUTHOR]

Highlights • The effect of opening ratios of burst disk has been experimentally investigated. • The burst disk cannot fully open and forms a divergent nozzle. • The mean shock speed and shock overpressure inside/outside the tube reduce significantly. • The minimum initial pressure for spontaneous ignition increases significantly when χ = 2/3. • When χ ≤ 1/2, no ignition occurs even though initial pressure ratio is as high as 90. Abstract Hydrogen is regarded as an alternative energy carrier in the next decades and high-pressure hydrogen storage is treated as the best option. However, unexpected spontaneous ignition would occur during high-pressure hydrogen sudden release, which induces a severe safety issue. For improving the safety application of hydrogen, an experimental investigation has been conducted. Different diameter ring gaskets are employed to change the opening ratio χ. Pressure transducers and light sensors are used to record the pressure variation and possible light signals inside the tube, respectively. It is found that the burst disk is unable to fully open during high-pressure hydrogen release when χ < 1, resulting in forming a convergent nozzle. This structure leads to the speed reduction for supersonic flow. Consequently, the speed of shock and shock overpressure inside the tube reduce significantly. The spontaneous ignition cannot be initiated even though the initial pressure ratio is as high as 90 when χ ≤ 1/2. The minimum initial pressure ratio required for spontaneous ignition increases to 64.1 when χ = 2/3. The flame is dimmer for small opening ratio cases. The shock overpressure outside the tube is reduced significantly, which decreases the damage to the facilities and humans to a large extent. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the effects of hydrogen additions on spontaneous ignition of high-pressure hydrogen released into hydrogen-air mixture. Hydrogen and air are premixed with different volume concentrations (0%, 5%, 10%, 15% and 20% H 2) in the tube before high-pressure hydrogen is suddenly released. Pressure transducers are employed to detect the shock waves, estimate the mean shock wave speed and record the shock wave overpressure. Light sensors are used to determine the occurrence of high-pressure hydrogen spontaneous ignition in the tube. A high-speed camera is used to capture the flame propagation behavior outside the tube. It is found that only 5% hydrogen addition could decrease the minimum storage pressure required for spontaneous ignition from 4.37 MPa to 2.78 MPa significantly. When 10% or 15% hydrogen is added to the air, the minimum storage pressure decreases to 2.81 MPa and 1.85 MPa, respectively. When hydrogen addition increases to 20%, the spontaneous ignition even takes place at burst pressure as low as 1.79 MPa inside the straight tube. Highlights • Effect of hydrogen doping to air on the spontaneous ignition occurrence is investigated experimentally. • Minimum storage pressure required for spontaneous ignition decreases with the increasing of hydrogen addition. • 5%, 10% and 15% hydrogen decrease minimum storage pressure from 4.37 MPa to 2.78, 2.81 and 1.85 MPa, respectively. • Spontaneous ignition takes place at storage pressure as low as 1.79 MPa when 20% hydrogen is added. [ABSTRACT FROM AUTHOR]

Combined effects of tube dimensions and burst pressure on the spontaneous ignition caused by high-pressure hydrogen release into a semi-confined space are investigated experimentally. An important finding is that the influence of tube diameter on spontaneous ignition shows complex behavior. For tubes with different diameters, the minimum burst pressure for spontaneous ignition depends on not only the strength of the shock wave but also the mixing of hydrogen and air. A dimensionless parameter of tubes, L/D —which is defined as the ratio of the tube length to the tube diameter—is introduced to describe the effect of tube size. The results show that the possibility of spontaneous ignition increases with increasing L/D . Under appropriate conditions, spontaneous ignition leads to flame development. As the flame propagates into a semi-confined space, it first forms an envelope structure in front of the hydrogen jet. Since some amount of a partially premixed combustible mixture, created by the hydrogen jet, exists in the semi-confined space, the flame subsequently undergoes deflagration. The overpressure caused by deflagration is significantly greater than that caused by the leading shock wave. In addition, both the deflagration overpressure and the shock-wave overpressure increase with increasing tube diameter and initial release pressure. [ABSTRACT FROM AUTHOR]

Hydrogen as an energy carrier is a very promising alternative fuel in the future. Accidental hydrogen explosions remain one of the major concerns in hydrogen energy utilization and process industries. This paper summarizes recent experimental and numerical efforts towards understanding combustion wave propagation in hydrogen explosions, including flame instabilities, flame acceleration, deflagrations, and deflagration-to-detonation transition (DDT). The fundamental problems involve understanding physical mechanisms that significantly influence the dynamic flame behavior in hydrogen explosions, such as combustion/hydrodynamic instabilities, vortex motion, pressure waves and flow turbulence. Advances achieved over recent years in new experimental observations, theoretical models and numerical simulations are discussed. Future research is required to quantitatively understand flame instabilities, turbulence properties and DDT in hydrogen explosions and improve reliability of theoretical and numerical predictions for hydrogen safety applications. [ABSTRACT FROM AUTHOR]

Nowadays, an effective and clean extinguishing agent or technology is highly desirable for lithium-ion battery (LIB) fires. Herein, the physicochemical properties and extinguishing effects of various extinguishing agents on 243 Ah lithium iron phosphate (LFP) battery fires are investigated systematically. The extinguishing mechanisms are deeply analyzed and the performance is comprehensively evaluated from the aspects of thermal runaway (TR) and toxicity suppression, cooling and extinguishing efficiency. Compared with HFC-227ea, C 6 F 12 O can absorb more heat through vaporization, thereby improving extinguishing and cooling efficiency. The lack of chemical inhibition effect and the tiny droplet size make water mist unable to suppress the high-temperature jet fire, but it has the lowest toxicity and highest cooling efficiency of 54.6%. F-500 and FireIce can improve the extinguishing performance of the water mist by encapsulating and taking hydrocarbon fuel away from the fire zone and inhibiting free radicals in the flame, respectively. 3% F-500 has the extinguishing efficiency of 78.4% and TR efficiency of 64.1%, while maintaining the cooling performance well. In the future, a novel type of fire-extinguishing agent with high heat capacity and latent heat, excellent extinguishing performance, high wettability, low toxicity and insulating properties is expected to be developed for LIB fires. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogen, which is considered to be a promising clean energy source, has been studied and applied extensively in industries. In order to improve the safety of hydrogen energy application, an experimental study on the influence of multi-layer wire mesh on dynamics of premixed hydrogen-air flame propagation in a closed duct is conducted. Four different kinds of wire mesh with 40, 45, and 50 layers are chosen in the experiments. High speed schlieren photography is applied to capture the flame shape changes and determine the flame tip speed. Pressure transducer is used to measure the pressure transient. It is found that flame quenches in the cases of adding wire mesh of 60, 80, and 100 mesh with 45 and 50 layers, while for the wire mesh of 40 mesh, 50 layers cannot even quench the flame. Moreover, the multi-layer wire mesh can effectively suppress the flame tip speed, maximum pressure, and sound waves during premixed hydrogen-air flame propagation in the duct. The attenuated maximum pressure reaches approximately 78.6% in the case of adding wire mesh of 100 mesh-50 layers. [ABSTRACT FROM AUTHOR]

Research surrounding premixed flame propagation in ducts has a history of more than one hundred years. Most previous studies focus on the tulip flame formation and flame acceleration in pure gas fuel-air flame. However, the premixed natural gas-air flame may show different behaviors and pressure dynamics due to its unique composition. Natural gas, methane and acetylene are chosen here to conduct a comparison study on different flame behaviors and pressure dynamics, and to explore the influence of different compositions on premixed flame dynamics. The characteristics of flame front and pressure dynamics are recorded using high-speed schlieren photography and a pressure transducer, respectively. The results indicate that the compositions of the gas mixture greatly influence flame behaviors and pressure. Acetylene has the fastest flame tip speed and the highest pressure, while natural gas has a faster flame tip speed and higher pressure than methane. The Bychkov theory for predicting the flame skirt motion is verified, and the results indicate that the experimental data coincide well with theory in the case of equivalence ratios close to 1.00. Moreover, the Bychkov theory is able to predict flame skirt motion for acetylene, even outside of the best suitable expansion ratio range of 6 < E < 8. [ABSTRACT FROM AUTHOR]

To investigate the effects of the geometry of downstream pipes on the shock ignition and the formation of the shock waves during high-pressure hydrogen sudden expansion, a series of bench-mark experiments were designed and high-pressure hydrogen were released into five types of pipes with different angles (60, 90, 120, 150 and 180°). It was found that the geometry of downstream pipes had a significant influence on the shock ignition of hydrogen. The incident shock wave would be reflected at the corner of the pipes with angles of 60, 90, 120 and 150°. The intensity of the reflected shock wave is higher if the angle is smaller. In addition, the average velocity of the leading incident shock wave would decrease when it passed the corner of the pipe. Using a pipe with smaller angle significantly increases the likelihood of shock ignition and lowers the minimal required burst pressure for shock ignition. The overpressure of the incident shock waves inside the exhaust chamber (for the cases with the angles of 60, 90, 120 and 150°) decreases sharply. There are three flame propagation behaviors inside the exhaust chamber: flame quenching, flame separation and no flame separation. The results of this study have implications concerning designs for storage safety of hydrogen energy and may help get better understanding of shock ignition mechanism of high pressure hydrogen and effect of pipeline geometry on ignition. [ABSTRACT FROM AUTHOR]

An experimental investigation of spontaneous ignition and flame propagation at high-pressure hydrogen release via cylindrical tubes with varying cross-section is presented. Tubes with different transverse cross-sections are considered in the experiments: (1) local contraction, (2) local enlargement, (3) abrupt contraction, and (4) abrupt enlargement. The results show that the presence of the varying cross-section geometries can significantly promote the occurrence of spontaneous ignition. Compared to the tube with constant cross-section, the minimum pressure release needed for spontaneous ignition for the varying cross-sections tubes is considerably lower. Moreover, the initial ignition location is closer to the disk in the presence of varying cross-section geometries in comparison with straight channel. As the flame emerges from the outlet of the tube, the velocity of the flame front in the vicinity of the nozzle increases sharply. Then, a deflagration develops across the mixing zone of hydrogen/air mixture. The maximum deflagration overpressure increases linearly with the release pressure. Subsequently, a hydrogen jet flame is produced and evolves different shapes at different release stages. A fireball is formed after the jet flame spouts in the open air. Later, the fireball develops into a jet flame which shifts upward and continues to burn in the vertical direction. [ABSTRACT FROM AUTHOR]

An experimental study on flow characteristics and spontaneous ignition produced by pressurized hydrogen release through an Omega-shaped tube into atmosphere was conducted. This paper aims to study the influence of geometry of downstream tube on the shock waves and the spontaneous ignition of pressurized hydrogen release. The tube used in present experiments is an Omega-shaped tube. It is found that the pressure of the tank will undergo an increase when hydrogen is releasing in the Omega-shaped tube because of the shock wave reflection which is detected by the piezoelectric pressure transducers. The pressure inside the Omega-shaped tube is much higher compared with straight tubes. Additionally, the spontaneous ignition even occurs inside the tube when burst pressure is as low as 2.19 MPa, which means that the geometry of downstream tube does have an important influence on the spontaneous ignition of hydrogen release and using an Omega-shaped tube reduces the critical pressure required for spontaneous ignition. When burst pressure is below 4.09 MPa, the spontaneous ignition occurs inside the tube and flame is formed inside the exhaust chamber but no flame separation happens. [ABSTRACT FROM AUTHOR]

Spontaneous ignition and subsequent flame propagation of high-pressure hydrogen release via a tube into air are experimentally investigated using pressure records, flame detection and direct high-speed photographs. The study shows that as the burst pressure increases the likelihood of spontaneous ignition increases and the initial ignition is closer to the burst disk. With the increase of tube length, the possibility of spontaneous ignition increases, while the critical release pressure for spontaneous ignition decreases. It is also found that a strong shock wave generated to trigger the ignition and a long tube to promote the growth of the flame are two key factors for the transition from spontaneous ignition inside the tube to jet flame in the air. After the flame exits from the tube, a flame envelope is formed in the front of the hydrogen jet, which gradually splits into upstream and downstream combustion regions. The upstream flame region propagates forward. However, the downstream flame region moves back toward the tube exit. The flame is then stabilized at the tube exit and gradually grows. Noticeable deflagration events were observed to occur successively in the semi-enclosed space. The deflagration leads to a significant increase of pressure in the chamber. And the overpressure of the deflagration is higher than that of the leading shock wave. Both the overpressures of the leading shock wave and the deflagration increase with the release pressure. A stable jet flame is formed outside the tube subsequent to the deflagration. And different jet flame configurations are observed at different controlling mechanisms of flow. [ABSTRACT FROM AUTHOR]

With the accelerating development of the hydrogen economy, more requirements are put forward for the detection capability of portable hydrogen sensors. Though the fast and accurate detection of hydrogen has been indispensable, there are still some challenges in the detection of extremely low concentrations of hydrogen. In this work, Pd-SnO 2 /rGO ternary nanocomposites with porous structures were synthesized by a facile template-free hydrothermal method. The effects of each element and its contents on the sensitivity and selectivity to hydrogen were systematically studied. The best hydrogen sensing property was produced by the synergistic effect of the 5.0 Pd-SnO 2 /rGO ternary nanocomposite, which showed a response of 32.38 toward 200 ppm hydrogen at 360 ℃. Especially, the response of 5.0 Pd-SnO 2 /rGO to 0.5 ppm (500 ppb) hydrogen reached 2.4, indicating the great potential in the detection of extremely low concentrations of hydrogen. The mechanism of high hydrogen sensitivity and selectivity was elaborated in combination with the analysis of band structure. All the as-prepared sensors exhibit quantitative concentration-response function relationships, favorable reversibility, and long-term stability. This work may provide a feasible strategy for the design of novel H 2 sensors with high sensitivity to extremely low concentrations of hydrogen. [Display omitted] • Self-assembled Pd-SnO 2 /rGO porous composites were synthesized by a facile method. • 5.0 Pd-SnO 2 /rGO exhibits an excellent response of 2.4 to ppb-level H 2 of 0.5 ppm. • Effects of different elements and contents on sensing properties were elucidated. • Excellent H 2 selectivity and stability were achieved by the synergistic effect. • The enhancement mechanism of sensing properties to H 2 is systematically studied. [ABSTRACT FROM AUTHOR]

The premixed flame dynamics and pressure build-up in a closed duct with a 90° bend are experimentally and numerically investigated, and compared to a previous analytical theory. Emphasis is placed on the effect of the bend on the flame propagation, especially on the detailed flame front evolution. The results show that the finger flame is curved along the bend. A noticeable tulip flame is produced in the horizontal straight section as the upper parts of the indented flame nearly catches up with the lower parts. The lower parts tend to dominate the flame propagation after the complete formation of the tulip flame. The tulip flame disappears with the vanishing of the upper parts near the end of combustion. The flame dynamics in the experiment is reasonably reproduced by the numerical simulations, especially with isothermal wall. It is found that the full formation of the tulip flame is accompanied by a second drastic flame deceleration arising from the rapid reduction of the surface area of the outer flame front near the outer sidewall. It is revealed that the takes on the appearance of a “trough” shape after the flame touches the outer walls. The flame is still concaved from the center toward the burnt gas after the disappearance of the tulip upper parts. The pressure rise is closely related to the flame behavior. The heat transfer through the duct walls has a significant influence on the combustion dynamics. Both the flame tip location and pressure rise in the later stages are greater in the case of adiabatic duct walls than in the experiment. The theoretical analysis demonstrates that the flame propagation mechanism in the early stages in the curved duct coincides with that in a straight duct despite the presence of the bend. However, the flame behavior after its contact with the duct sidewall and tulip formation differs from those in a straight duct under the effects of the bend. [ABSTRACT FROM AUTHOR]

The residual electricity contained in spent lithium-ion batteries probably triggers the thermal runaway and results in irreparable disaster during recycling. Chemical discharge is a common method to eliminate hazards by immersing batteries in an aqueous solution to release the remnant energy. However, a high-efficiency discharge solution usually causes severe corrosion of the battery shell, inducing safety accidents. In this work, theoretical and experimental studies are carried out in various solutions to investigate the efficiency and corrosion of chemical discharge strategy. The results suggest that zinc acetate solution is a potential discharge medium with excellent comprehensive properties compared with NaCl, MnSO 4 , FeSO 4 , and KAc solutions. Electrolytic reactions and external short circuit have been proved to be the essential causes of high discharge efficiency. Adsorption theory and Kolbe reaction are used to explain the low corrosion of battery shells in acetate solutions. Besides, the thermal stability of treated spent batteries also validates our discharge strategy's feasibility and ensures safety during transportation, storage, and recycling. The high-efficiency discharge mechanism and excellent corrosion inhibition of spent lithium-ion battery immersing in zinc acetate solution. [Display omitted] • Electrolysis and external short circuit ensure the high discharge efficiency. • Manganese sulfate cannot effectively discharge spent batteries. • Zinc acetate solution is first proposed as a potential discharge medium. • Adsorption theory and Kolbe reaction explain the low corrosion in acetate solution. [ABSTRACT FROM AUTHOR]

Shock waves and spontaneous ignition produced by pressurized hydrogen release through a tube into atmosphere are studied experimentally. The results showed that the speed of the leading shock wave increases at the initial stage and then decreases when propagating to the downstream inside the tube. The schlieren images of the of the hydrogen jet in the vicinity of the tube exit clearly show various classical flow structures, i.e. Mach disk, barrel shock, reflected shock and shock triple point. Due to the sharp decline of the strength of the shock wave, spontaneous ignition might be difficult to occur or quenched outside the tube. Additionally, Spontaneous ignition is more likely to happen in the downstream tube with small diameter and the possibility of spontaneous ignition increases with increasing the tube length. An accidental explosion was observed when the hydrogen jet was emitted into a semi-closed exhaust chamber. It is found that the rupture process of the diaphragm has an important influence on the formation of shock wave and spontaneous ignition. [ABSTRACT FROM AUTHOR]

Abstract: The dynamics of premixed hydrogen/air flame ignited at different locations in a finite-size closed tube is experimentally studied. The flame behaves differently in the experiments with different ignition positions. The ignition location exhibits an important impact on the flame behavior. When the flame is ignited at one of the tube ends, the heat losses to the end wall reduce the effective thermal expansion and moderate the flame propagation and acceleration. When the ignition source is at a short distance off one of the ends, the tulip flame dynamics closely agrees with that in the theory. And both the tulip and distorted tulip flames are more pronounced than those in the case with the ignition source placed at one of the ends. Besides, the flame–pressure wave coupling is quite strong and a second distorted tulip flame is generated. When the ignition source is in the tube center, the flame propagates in a much gentler way and the tulip flame can not be formed. The flame oscillations are weaker since the flame–pressure wave interaction is weaker. [Copyright &y& Elsevier]

• The minimum release pressure for self-ignition is significantly higher. • The decrease of binary mixture self-ignition enhances with fuel molecular weight. • Nitrogen addition effectively inhibits flame development inside the tube. • Nitrogen-weaken ignited flame spouting from tube exit tends to blow out. • When self-ignition occurs, a partially premixed flame evolves first. This paper reports on the nitrogen addition effects on the self-ignition of high-pressure hydrogen leakage. It reveals that the intensity of produced incident shock decreases with more nitrogen addition, unbeneficial for self-ignition occurrence. Besides, nitrogen addition in hydrogen significantly reduces self-ignition possibilities inside the tube and self-sustained jet flame formation outside the tube. There exists a certain critical threshold of shock overpressure of about 1 MPa for self-ignition occurrence at different nitrogen additions. In our experiments, the impurity gases (N 2 , CO, CH 4) reduce the self-ignition possibilities in the same order as it reduces the shock intensity, namely, the effect of N 2 is similar to that of CO, larger than that of the same volume of CH 4. It suggests that the decrease of binary mixture self-ignition can be mostly explained by the reduction of shock intensity, and the decrease effect enhances with fuel molecular weight. Furthermore, nitrogen addition inhibits the flame development and propagation inside the tube. Nitrogen-weaken ignited flame barely survives during the expansion outside the tube or is soon extinguished inside the tube with more nitrogen addition. Moreover, the flame has a rapid flame length growth rate of 1–2 mm/μs in the initial stage, but the expanding velocity becomes lower to 0–1 mm/μs after a period of spread. Accordingly, a mechanism of the self-ignition process for high-pressure hydrogen release is proposed for cases with 0%-7.5% nitrogen addition. [ABSTRACT FROM AUTHOR]

• The internal temperature of the cell was measured to study the temperature rebound. • The cooling effect of intermittent spray with different periods and duty cycles were studied. • The gas toxicity of LIBs under a different SOC and water spray was evaluated. The fire extinguishing and cooling of lithium-ion battery thermal runaway have attracted significant research attention. In this study, an intermittent spray method for cooling lithium-ion battery during thermal runaway is proposed. The internal temperature and voltage of the battery, as well as the gases generated during thermal runaway are investigated. In addition, the extinguishing and cooling ability of the intermittent spray method at different intermittent periods (cycle consisting of a spray time and an interval time) and duty cycles (the percentage of the pulse duration occupied in a cycle) are compared and discussed. Furthermore, the toxic effects of the generated gases are evaluated. Experimental results reveal that the internal temperature of the battery is significantly higher than the surface temperature during the thermal runaway. Particularly, the internal temperature of the cell with 100% state of charge was as high as approximately 1000 ℃. In addition, the surface temperature of the cell may rebound after cooling owing to the insufficient heat transfer and a large radial temperature gradient of the battery. Furthermore, intermittent spray with more spray pulses of shorter duration performs better cooling effect. Particularly, the cooling effect initially increases, and then decreases with decreasing duty cycle. The major toxic gases produced during thermal runaway are CO and HF, whose yield increases with an increase in the state of charge, and the toxicity of these gases increases after the water spray. The findings of this study indicate that strict safety protection is needed when water spray is used to extinguish LIB fires. [ABSTRACT FROM AUTHOR]

Thermal runaway initiated in an individual cell may transfer heat to adjacent cells, and cause thermal runaway propagation. Thus, mitigation and prevention of thermal runaway propagation using extinguishing agents are significant. In this work, fire and extinguishing tests on 117 Ah LIBs with Li(Ni 0.8 Co 0.1 Mn 0.1)O 2 (NCM)/graphite electrodes are investigated. The suppression effects of different extinguishing agents including HFC-227ea, C 6 F 12 O and water spray on thermal runaway propagation in confined space were compared. Results show that thermal runaway propagation can occur in LIBs module even with thermal management measures. When activated immediately after the thermal runaway of the first cell, each agent can extinguish the LIBs module fire. However, the cooling capacity of extinguishing agent is the key factor to suppress thermal runaway propagation. The heat dissipation of HFC-227ea, C 6 F 12 O and water spray in fire extinguishing test is 24.8 kJ, 111 kJ and 459.8 kJ, respectively. Thus, HFC-227ea can hardly suppress the thermal runaway propagation. Although C 6 F 12 O can not prevent thermal runaway propagation, it can decrease the battery temperature, slow down the heat transfer rate and prolong the propagation time. While water spray has the best cooling effect, which can prevent thermal runaway propagation. [ABSTRACT FROM AUTHOR]

• Shock wave is temporarily weakened when the shock wave travels through obstacles. • Effects of obstacles in the tube on hydrogen self-ignition is investigated. • The further obstacles away from diaphragm, the more probability of flame enhancement. • Presence of obstacles in tube would only temporarily promote combustion inside tube. The spontaneous ignition and subsequent hydrogen combustion has become a great challenge for the safe use of hydrogen energy at high-pressure. The spontaneous ignition mechanism of high-pressure hydrogen in the tube with obstacles has still not fully understood. In this study, synchronization measurement was performed through simultaneous pressure and flame acquisition, and experiments of pressurized hydrogen sudden release through tubes with obstacles were conducted. Spontaneous ignition and subsequent hydrogen combustion were reproduced through varying initial burst pressure in different obstructed tubes, the presence of obstacles exhibit great influence on shock wave propagation and flame evolution inside the tube. The temporary weaken of shock wave strength caused by obstacles is not conducive for spontaneous ignition onset. At the contrary, the complex dynamic flow induced by obstacles facilitates the occurrence of the spontaneous ignition. The effect of obstacles on the spontaneous ignition onset can be further analyzed by the minimum burst pressure for spontaneous ignition. And it shows the effects of obstacles on spontaneous ignition onset depends on its comprehensive influences on the formation of hydrogen/air mixture and increment of temperature. Furthermore, locations of obstacles also play an essential role on spontaneous ignition onset and hydrogen combustion intensity inside tube. The pressure and flame dynamics evolution show that when increasing the distance between burst disk and obstacles, the obstacles exhibit less influence on the spontaneous ignition onset but temporarily enhance combustion inside tube. [ABSTRACT FROM AUTHOR]

This work investigated the effects of water spray on lithium-ion battery (LIB) fires. Experiments were conducted on single cell and multi-cell batteries to study the effect of water volume and spray pressure on the fire extinguishing and the effectiveness of preventing propagation of thermal runaway in LIB's. Meanwhile, the potential hazard of water spray as a fire extinguishing method was assessed by investigating the influence of water on combustion gas production during extinguishing. It was found from these experiments that water spray can effectively extinguish 21700 LIB fires and reduce the maximum surface temperature of LIB. But the water spray has no significant difference in cooling rate after temperature recovery. The contact efficiency between the water spray and batteries decreased with the increase in water pressure. With sufficient volume of water spray and high contact efficiency, water spray can inhibit the thermal runaway propagation. With insufficient volume of water spray or low contact efficiency, the time to onset of thermal runaway was delayed. Water affects combustion gas production during thermal runaway. When water was applied, the concentration of CO, H 2 and HF increased, while CO 2 decreased. • The cooling and suppression effect of water spray on LIBs fire were investigated. • The cooling efficiencies and mechanisms of water spray were studied. • The variations in gas production during the extinguishing process were investigated. [ABSTRACT FROM AUTHOR]

Larger thermal stress can lead to capacity fade and safety issue of lithium-ion batteries. Thermal expansion is induced by thermal stress due to the temperature deviation during charge-discharge cycles. In this study, the thermal expansion behavior for a 38 Ah prismatic ternary battery is identified by presenting a three dimensional thermal-mechanical model. Corresponding experiments are conducted to measure the internal resistance and Young's modulus that are decisive for the results. Then the model is validated by the temperature response at different discharge currents, and parameters sensitivity analysis is carried out to evaluate the uncertainty of the model. Based on the model, the temperature distribution is revealed over the cell that the temperature follows the sequence from high to low that is cell, positive tab, and negative tab; the temperature difference between two tabs is larger than that between positive tab and battery cell. The stress exhibits correlation with temperature gradient that enhanced von-Mises stress is observed at inner center of cell as elevated temperature levels. The simulation results also provide insight into the von-Mises stress and displacement along three directions (width, thickness and height) of the battery at different depth of discharge and current. It is found that larger thermal stress and expansion are observed with increasing current and depth of discharge, as well as at the boundary constraints. Besides, the battery expands more along the thickness direction and the tab portion where the temperature is higher. The maximum thermal average volume stain aroused by temperature difference during discharge at 1 C is 1.04 × 10 − 4 . • Implementation of a 3D fully-coupled thermal-mechanical model at cell level. • Expansion induced macroscopic mechanical stress due to thermal gradient. • Determination of Young's modulus and thermal validation for a 38 Ah prismatic cell. • Enhanced von-Mises stress at inner center of cell as elevated temperature levels. • Thermal expansion depends on the current, DOD and the location on cell. [ABSTRACT FROM AUTHOR]

• The critical pressure for ignition increases with methane addition concentration. • Methane addition can effectively inhibit flame development in the tube. • Three mechanisms of self-ignition for hydrogen with methane addition is proposed. • Hydrogen-methane flame spouting from tube exit tends to blow out. • The hydrogen-methane mixture brings greater combustion overpressure in chamber. In this paper, experimental investigations are carried out to study the effects of methane addition (2.5%, 5% and 7.5% vol.) on self-ignition and subsequent flame propagation of pressurized hydrogen release via a tube. The visualization method utilizing the high-speed direct photography and the measurements of pressure and light sensors are applied in this study. The result shows that the existence of methane can reduce the shock wave overpressure and the temperature of shock-heated air. Therefore, it has great effects on the self-ignition possibility. The minimum burst pressure required for self-ignition increases from 2.89 MPa (0% CH 4) up to 6.05 MPa (7.5% CH 4). Besides, methane addition can extremely reduce flame intensity and inhibit flame development inside the tube. Three possible self-ignition mechanisms for the hydrogen with methane addition are discussed. Under the effects of methane addition, hydrogen flame spouting from tube exit tends to blow out. In all cases with 7.5% methane addition, no self-sustained jet flame is formed outside the tube for burst pressure up to 10.0 MPa. When self-sustained flame is formed in a confined space, a great rise in overpressure is generated due to the intense combustion. It is suggested that more methane addition can reduce the self-ignition probability and the formation of self-sustained flame. However, with the increasing of CH 4 additions, once the jet fire is formed in a confined space, it may cause greater overpressure and thus bring greater casualties and property losses. [ABSTRACT FROM AUTHOR]

In this study, an experimental investigation is conducted to study the effects of CO addition (0%–7.5% vol.) on the self-ignition of pressurized hydrogen leakage. The result shows that more CO addition significantly decreases the likelihood of self-ignition inside the tube and the formation of self-sustained jet flame outside the tube. This can be mostly explained by the reduction of leading shock intensity inside the tube. Furthermore, CO addition effectively inhibits the flame propagation and development inside the tube. For pure hydrogen, the ignited flame quickly develops an intense flame spanning the tube width and eventually form a jet flame in ambient air. However, the H 2 –CO diffusion flame initiated approaching tube sidewall tends to propagate adjacent to the wall or be soon quenched with more CO addition. If the CO-weakened flame spouts to the tube exit, it may not survive the expansion at the tube exit and thus it is quenched. • The shock intensity is reduced in the presence of CO. • The critical pressure for self-ignition increases with CO addition concentration. • Shock intensity variation by CO addition is the main factor affecting self-ignition onset. • Small CO addition can effectively inhibit flame development inside the tube. • H 2 –CO flame spouting from the tube exit tends to be blown out. [ABSTRACT FROM AUTHOR]

Spontaneous ignition induced by high-pressure hydrogen release is one of the huge potential risks in the promotion of hydrogen energy. However, the understanding of the microscopic dynamic characteristics of spontaneous ignition, such as ignition initiation and flame development, remains unresolved. In this paper, the spontaneous ignition caused by high-pressure hydrogen release through a tube is investigated by two-dimensional numerical simulation at burst pressure ranging from 2.67 to 15 MPa. Especially, the thermal and species characteristics in hydrogen shock-induced ignition under different strengths of shock wave are discussed carefully. The results show that the stronger shock wave caused by higher burst pressure leads to larger heating area and higher heating temperature inside the tube, increasing the possibility of spontaneous ignition. The shortening effect of initial ignition time and initial ignition distance will decrease with the increase of the burst pressure. Ignition will be initiated when the temperature is raised to about 1350–1400 K under the heating effect of shock waves. It is also found that the ignition occurs under the lean-fuel condition firstly on the upper and lower walls of the tube. The flame branch after spontaneous ignition is observed in the mixing layer. Two ignition kernels show different characteristics during the process of combustion and flow. The evolution of HRR and mass fraction of key species (OH, H, HO 2) are also compared to identify the flame front. The mass fraction of H has the better trend with HRR. It is suggested that H radical is a more reasonable choice as the indicator of the flame front. • The spontaneous ignition of the high-pressure hydrogen is numerically investigated. • Ignition will be initiated when the temperature rises to 1350–1400 K. • Ignition occurs under the lean-fuel condition firstly. • Branch of flame is observed in the mixing layer after spontaneous ignition. • The evolution of HRR and key species is analyzed. [ABSTRACT FROM AUTHOR]

Although the thermal decomposition of nitrocellulose (NC) has been comprehensively examined, the effects of nitrogen content on the pyrolysis behavior of NC have not been clearly elucidated. In this work, the macro- and microstructures of NC samples with varying nitrogen contents were qualitatively and quantitatively analyzed. Higher nitrogen contents in NC samples were found to be associated with an increased number of nitro groups and cracks in the fiber surface. To elucidate the NC pyrolysis process and provide a theoretical basis for enhancing its stability, the pyrolytic behavior of NC was examined using thermogravimetric analysis-Fourier transform infrared spectrometry and pyrolysis-gas chromatography-mass spectrometry. The pyrolysis of NC primarily occurred within a temperature range of 180–240 °C; however, the peak temperature of the mass loss rate decreased with increasing nitrogen content. The initial nitrogen oxide produced by pyrolysis was nitrogen dioxide (NO 2). During the main stage of pyrolysis, a wider variety of gases was produced by NC having a higher nitrogen content, with more cyclization recombination forms occurring in the post-reaction stage of pyrolysis. Based on the findings of this study, a detailed process of NC pyrolysis has been proposed. [ABSTRACT FROM AUTHOR]

• Three kinds of 3D models with different units are proposed for a li-ion battery. • Thermal behavior is compared among the three models. • Several typical electrochemical properties are compared with the three models. • One unit model can replace the full-scale model for simplifying calculation. Recently, lithium-ion battery system appears to be an effective approach for energy storage due to their excellent performances. The internal structure of the lithium-ion pouch cell is laminated and is composed of several repeated units, and the unit includes five parts of positive current collector, positive electrode, separator, negative electrode and negative current collector. This structure brings great difficulties for simulator to develop full-scale model of the battery due to the complex calculation. In this paper, three kinds of three-dimensional layered electrochemical-thermal models with different unit numbers, one unit model (OUM), two unit model (TUM), and half-scale model (HSM) are established to study the effect of number of units on lithium-ion battery thermal behavior and electrochemical characteristics under adiabatic condition. The corresponding experimental procedure is performed for model validation, the simulation and experiment are in good agreement with temperature and discharge curves at four different discharge rates (0.5 C, 1 C, 1.5 C and 2 C). The results show that the temperature distribution and heat generation rate per volume as well as the representative electrochemical properties are almost the same of the three models; it is also found that each unit of the TUM and HSM is uniform and symmetrical distributed. Therefore, the HSM and full-scale model can be replaced by the OUM for lithium-ion pouch cell under adiabatic condition. The OUM can save 1/140 of computing time and greatly reduce the computational resources compared to HSM, which can facilitate the related research under adiabatic. [ABSTRACT FROM AUTHOR]

Because of the inconsistency in battery pack and failure of charging device, slight overcharging of lithium ion batteries appears and even causes to thermal runaway. The aging behavior and mechanisms of lithium ion battery under slight overcharging cycling are studied qualitatively and quantitatively based on incremental capacity analysis and electrochemical impedance spectroscopy in this work. The results show that slight overcharging accelerates battery aging because of the loss of active material. While, conductive loss influences capacity fading less. The effect of lithium density loss is in the middle level. So it is suggested that incremental capacity analysis and impedance estimation are used to detect overcharging cycling on-line. Furthermore, the thermal stability of aged batteries are studied using Extended Volume Accelerating Rate Calorimeter. The results show that the stability of aged batteries become worse. The anode plays a key role in the thermal stability changes because of lithium plating under overcharging. The cathode dominates the stability after 70% SOH because of structure damage of cathode. • Thermal stability of aged battery caused by slight overcharging cycling is studied. • Aging behavior and mechanisms of slight overcharging cycling are revealed. • Cathode and anode play different roles in different aging stages. • Changes of thermal stability of aged battery are explained by aging mechanisms. [ABSTRACT FROM AUTHOR]

[Display omitted] • MOF-derived porous xPd-NPs@ZIF-8/ZnO were prepared by optimized heat treatment. • Ultrafast high response properties of the sensors were achieved under UV excitation. • Coupling effects of photoexcitation and thermal excitation were explored in detail. • The sensing mechanism of the superior performances were systematically studied. Metal-organic frameworks (MOFs) have been regarded as a potential candidate with great application prospects in the field of gas sensing. Although plenty of previous efforts have been made to improve the sensitivity of MOF-based nanocomposites, it is still a great challenge to realize ultrafast and high selectivity to typical flammable gases in a wide range. Herein, porous xPd-NPs@ZnO were prepared by optimized heat treatment, which maintained the controllable morphology and high specific surface area of 471.08 m2g−1. The coupling effects of photoexcitation and thermal excitation on the gas-sensing properties of nanocomposites were systematically studied. An ultrafast high response of 88.37 % towards 200 ppm H 2 was realized within 1.2 s by 5.0Pd-NPs@ZnO under UV photoexcitation. All xPd-NPs@ZnO exhibited favorable linearity over an extremely wide range (0.2–4000 ppm H 2) of experimental tests, indicating the great potential in quantitative detection. The photoexcited carriers enabled the nanocomposites a considerable response at lower operating temperatures, which made diverse applications of the sensors. The mechanisms of high sensing performances and the photoexcitation enhancement were systematically explained by DFT calculations. This work provides a solid experimental foundation and theoretical basis for the design of controllable porous materials and novel photoexcited gas detection. [ABSTRACT FROM AUTHOR]

This paper studies the effects of triangle obstacles inside the tube on the ignition mechanism and subsequent flame development in a semi-confined space when high-pressure hydrogen sudden release. Smooth tube and obstructed tube with optical glasses are constructed where controlled high-pressure hydrogen are released. High-speed direct photography is used to image the flame evolution while pressure transducers are used to obtain pressure-time traces both inside the tube and exhaust chamber. These cases that hydrogen with various burst pressure jets into the smooth and obstructed tubes are tested. It is found that spontaneous ignition occurs in the boundary layer of the tube in the smooth tube, a complete fire spanning the cross-section is reached as the flame propagates within the mixing region. The appearance of obstacles is found to have a significant effect on the ignition mechanism and flame structure. A two-way dissemination reflected shock wave forms and three possible ignition region emerges surrounding the obstacles. The flame propagation restricted between the leading shock wave and hydrogen jet. The flame experiences a split that the front flame in the vicinity of the obstacle gradually dies out and the rear flame continues propagating within the mixing region. The flame evolution and pressure variation in the exhaust chamber show that obstacles inside the tube do not aggravate the disaster in the semi-confined chamber. [ABSTRACT FROM AUTHOR]

Hydrogen, as the promising clean alternative energy in the future, is in the spotlight now all over the world. However, its flammable and explosive hazards should be highly considered during its practical application. In this study, the experiments are performed to study premixed hydrogen-air flame propagation in the duct with pellets bed, especially for fuel-rich condition. High-speed schlieren photography is employed to capture flame front development during the experiments. As well as the pressure transducer, is used to track the pressure buildup in the flame propagation process. Different diameters of pellets and different concentrations of gas mixture are considered in this experimental study. The typical evolutions about the tulip flame are similar in all cases, although the tulip flame formation time caused by the laminar flame speed are different. The flame propagation velocity is pretty enhanced in fuel-lean mixture under the effect of large diameter pellets bed, but it is significantly suppressed in fuel-rich conditions. While for the small diameter pellets (d = 3 mm), the suppression effect on flame propagation and pressure is obtained over a wider range of equivalence ratios, especially a better suppression effect is generated near the stoichiometric condition. • Tulip flame formation time is influenced by the pellets bed only at Ф = 5.6. • Suppression effects on flame velocity and pressure are shown at fuel-rich condition. • The smaller pellets or porosity, the better effect on absorbing pressure. • The flame may accelerate in the interaction process between flame and pellets bed. • Small diameter pellets present suppression effect both for lean and rich condition. [ABSTRACT FROM AUTHOR]

For the purpose of solving the safety problems of fire and explosion which may occur during hydrogen pipeline transportations, this paper experimentally investigates premixed hydrogen-air flame quenching behaviors under action of metal wire mesh in a closed tube. High-speed schlieren photography system is employed to reveal flame quenching results. Pressure transducer is adopted to test pressure changes. View from schlieren images, it is found that the wire mesh significantly enhances wrinkles of inverted flame front in lean-fuel combustion case (Φ = 0.42), but weakens the flame inversion extent for Φ = 1.00, 1.59, and 2.38 conditions. In addition, the results indicate that the flame quenching performance is improved pretty as the volume of metal wire mesh (V M) increases. Besides, compared with lean-fuel combustion cases, the wire mesh presents a more effective suppression effect on rich-fuel cases due to the coupling suppression effects on pressure waves and combustion process together. Moreover, it is found that the critical quenching speed increases linearly as V M increases, but the maximum critical quenching pressure is always kept at a constant value of approximately 0.115 MPa. The results may provide a significant reference for designing hydrogen flame arrestors to improve the safety of hydrogen pipeline transportations and engineering applications. [ABSTRACT FROM AUTHOR]