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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]

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]

In order to explore methods for suppressing methane combustion and improve the safety of its engineering application. The effect of single-layer wire mesh on premixed methane-air flame behaviors and pressure dynamics in a closed pipe is experimentally investigated. Premixed methane-air mixture with stoichiometric ratio is used in our experiments. The wire mesh of seven different types are chosen. High-speed schlieren photography system and pressure transducers are adopted to record flame behaviors and pressure-time history, respectively. It is found that the flame can easily pass through the wire mesh of 12 and 20 mesh, but extinguishes under the effect of 30 mesh. For 40, 60, 80, and 100 mesh conditions, the flame presents salient quenching trend but finally passes through wire mesh. Meanwhile, the wire mesh has been seriously destroyed. The results indicate that anti-destructive is quite important for the fire resistance capacity of wire mesh. Moreover, the wire mesh significantly advances tulip flame formation time and makes flame front inversion extent weaker due to its effect on advancing and weakening the interactions between flame front and pressure waves. Furthermore, almost no suppression effect on flame tip speed is observed in the upstream pipe because the reduction of gas flow velocity is counteracted by the growth of gas combustion velocity. However, the flame propagation in the middle suppression section is significantly inhibited due to the great heat losses when touching wire mesh. Besides, the maximum pressure is decayed significantly. And the suppression effect is pretty enhanced as mesh of wire mesh increases. • Single-layer wire mesh makes tulip flame formation time significantly advanced. • Flame front inversion extent presents weaker under the impact of wire mesh. • Anti-destructive is quite important for the fire resistance capacity of wire mesh. • Almost no inhibition on flame propagation speed is obtained in the upstream pipe. • The maximum pressure is effectively decayed by increasing the mesh number. [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]

With the fast development of manufacturing industry, rotary swaging technology is applied more and more widely in automobile, aviation and aerospace industries, due to its advantages such as saving materials, reducing lead time and improving product quality. Rotary swaging technology is mainly used to fabricate tubes, rods or act as preprocessing of other process. For instance, it can conduct necking of the tube ends before tube hydroforming process and internal gear machining process. In this paper, finite-element simulations using Forge 2011 3D has been carried out to investigate the rotary swaging process of tubes. According to the swaging method and presence of mandrel, rotary swaging process of tubes includes four categories, infeed method without mandrel, infeed method with mandrel, recess method without mandrel and recess method with mandrel. Metal flow and stress state of those four kinds of method are investigated. For the infeed method without mandrel, the metal mainly flows radially at the sinking zone. At the sizing zone, the metal flows axially with small velocity. When a mandrel is used, the axial flow velocity at the sizing zone gets larger. For the recess method, the main deformation area is the forging zone. The metal mainly flows radially at the forging zone with large velocity. Experiments have been carried out. Discrepancy of the tube thickness between the experiments and simulations for the infeed swaging without mandrel is less than 1.1%. [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]

Aiming to gain sufficient data to develop methods capable of predicting and evaluating the danger of potential explosion or even detonation hazards associated with industrial process piping systems, this paper experimentally studied the effect of equivalence ratio on flame acceleration and deflagration-to-detonation transition (DDT) of hydrogen-oxygen mixture in a channel equipped with continuous triangular obstacles. This obstruction can simulate the effect of continuous blockage or rough walls in process pipelines. High-speed schlieren photography and OH* chemiluminescence recording were used for visualization. Results show that significant vortex motion accelerates the delayed combustion between obstacles and generates strong jet flow to promote flame acceleration. DDT occurs when the equivalence ratio (Φ) is from 0.25 to 2.5. Minimum detonation initiation time and distance are obtained at Φ = 1.0 and 1.1. The equivalence ratio significantly influences DDT by affecting deflagration speed and shock strength. DDT mechanism for equivalence ratios closer to 1.0 is the survival of local detonation generated by intricate flame-shock interactions. While for equivalence ratios far from 1.0, i.e., extremely lean or rich fuel (Φ = 0.25, 2.0 and 2.5), DDT can be formed due to a combined effect of viscous heating at the boundary layer and preheat caused by shock compression. [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]

• Different flame behaviors with three different ignition positions are compared. • A special tulip flame is observed when the flame starts near the metal wire mesh. • Pressure decay is advanced by setting ignition position closer to metal wire mesh. • Flame becomes easier to quench as ignition position be closer to metal wire mesh. For obtaining effective inhibitory strategies for hydrogen combustion in terms of safety, the effect of ignition position on premixed hydrogen-air flame quenching behaviors under action of metal wire mesh is experimentally analyzed. Combustible hydrogen/air gases with volume ratio of 2:3 is adopted. Metal wire mesh of 60 meshes-60 layers is selected as the flame inhibitory structure. Three different ignition positions are arranged for obtaining different stages of flame entering suppression section. The results indicate that ignition position affects flame quenching results significantly. The flame quenching difficulty increases as the distance between ignition position and wire mesh location increases. Besides, the ignition position influences flame behaviors greatly. Tulip flame is actually led by the vortices in IP1 case, and the internal mechanism is attributed to the interactions of flame front and pressure waves. However, for IP3, the special tulip flame with an extremely long inversion cusp is actually led by the enhanced reverse gas flow in burnt field, and the root cause is metal wire mesh enlarges the discrepancies of combustion intensity between flame propagating toward positive and negative directions. Moreover, the ignition position changes flame tip speed and pressure greatly. As ignition position changes from IP1 to IP2 and IP3, the maximum flame tip speed toward positive direction decreases from 120.5 m/s to 105.2 m/s and 56.9 m/s, separately. Also, the maximum pressure reduces from 0.13 MPa to 0.08 MPa and 0.07 MPa, respectively, which further proves a more pronounced inhibitory effect when setting ignition position closer to wire mesh. [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]

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]

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]

Thermal runaway propagation (TRP) of lithium iron phosphate batteries (LFP) has become a key technical problem due to its risk of causing large-scale fire accidents. This work systematically investigates the TRP behavior of 280 Ah LFP batteries with different SOCs through experiments. Three different SOCs including 40 %, 80 %, and 100 % are chosen. In addition to key TRP characteristic parameters such as temperature, TRP time and speed are analyzed, more importantly, the energy flow distribution during the TRP of large-size LFP module is also revealed. The results indicate that among the three groups of modules, TRP occurs only in the module with 100 % SOC, which is attributed to the higher internal energy (666.11 kJ) and heat transfer power (264.07 W). For the module with 100 % SOC, the TRP time interval fluctuates from 667 s to 1305 s, and the TRP speed is in the range of 0.05–0.12 mm/s. Furthermore, the energy flow distribution indicates that more than 75 % of the energy is used to heat battery itself, and approximately 20 % is carried out by ejecta. Less than 10 % can trigger neighboring batteries into thermal runaway. This work may provide important guidance for the process safety design of energy storage power stations. [ABSTRACT FROM AUTHOR]

• Upward leakage significantly increases the likelihood of hydrogen accumulation, resulting in higher concentrations of hydrogen near the roof of the leak location and its surrounding areas within the garage. • Hydrogen diffusion through the roof preferentially spreads from the leakage location to the four immediately adjacent areas. • The volume of hydrogen concentration surpassing the lower explosion limit of hydrogen (18.3 %) is particularly elevated in the case of vertical downward leakage, attributed to the accumulation of hydrogen beneath the vehicle. • Horizontal leakage emerges as the least severe among the three leakage directions, resulting in the smallest overrun volume. Hydrogen leakage in confined spaces poses significant safety risks in hydrogen energy applications, potentially leading to fires and explosions. This paper focuses on the accident scene of hydrogen leakage and dispersion in underground parking garages. A medium-scale model (1/10) of an underground parking garage is designed and built to study the characteristics of the dispersion of hydrogen leaked from hydrogen fuel cell vehicles (HFCVs) in underground garages using experimental and numerical simulation methods. This paper focused on analyzing the dispersion characteristics of hydrogen leaked from hydrogen fuel cell vehicles (HFCVs) within these environments, with particular attention given to the influence of leakage direction—upward, horizontal, and downward—on hydrogen concentration distribution over space and time. For instance, it was observed that under equivalent flow rates, upward leakage tends to result in higher hydrogen concentrations at the leakage site. Conversely, downward leakage promotes wider hydrogen diffusion around the source, particularly evident at higher flow rates. Horizontal leakage, comparatively, exhibits lower risk due to greater air volume absorption. Complementing the experimental data, numerical simulations revealed consistent patterns in hydrogen diffusion. Specifically, the simulations illustrated a cyclic accumulation-diffusion-accumulation process. Notably, vertical upward leakage demonstrated the largest volume of regions exceeding a 4 % hydrogen volume fraction, whereas vertical downward leakage resulted in the greatest volume of regions surpassing an 18.3 % hydrogen volume fraction. This disparity arises from hydrogen accumulation beneath the vehicle in cases of vertical downward leakage. Conversely, regions of high concentration induced by horizontal leakage were the smallest. The study offers valuable insights for the design and construction of HFCVs and parking facilities, providing a theoretical framework for enhancing safety measures. [ABSTRACT FROM AUTHOR]

Exposure of LIB to high temperatures may cause certain damage or even fail to work. In this study, the electrochemical performance, the thermal stability and the critical heat of 18650 LIBs with/without water mist after high-temperature impact are experimental investigated. The results demonstrate that water mist raises the critical temperature of battery damage by about 40 °C. With increasing temperature, the electrochemical performance of the battery decreases, primarily caused by loss of lithium-ion. Moreover, water mist also improves the thermal stability of batteries after high-temperature impact, as demonstrated by the higher onset temperature of thermal runaway and activation barriers. Under the use of water mist, the critical heat that the battery performance is not affected and the critical heat for battery damage are obtained based on the increase and distribution of temperature and double integral, which are 2489.46 ± 47.7 J and 4777.63 ± 71.55 J, respectively. This work reveals that water mist could alleviate the damage to the battery caused by high-temperature impact, but when the heat exceeds the critical heat, the damage is irreversible. These findings could provide suggestions for the use of water mist in the thermal safety design of batteries in the future. [ABSTRACT FROM AUTHOR]

• 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]

With the increasing deployment of large-scale lithium ion batteries (LIBs), thermal runaway (TR) and fire behavior are significant potential risks, especially for high energy density cells. A series of thermal abuse tests and hazard analysis on 117 Ah LiNi 0.8 Co 0.1 Mn 0.1 O 2 /graphite LIBs were performed under two conditions, "open space" and "confined space". In open space tests, the fire behavior of LIBs was characterized with respect to the TR process, temperature characteristics, mass variation, voltage, heat release rate and gas release. To simulate the application scenarios in electric vehicles, a confined cabinet was introduced. The effects of state of charge and confined cabinet on the fire behavior of individual cell were analyzed. Furthermore, a real-scale scenario was considered for the evaluation of fire-induced toxicity using Fractional Effective Dose (FED) and Fractional Effective Concentration (FEC) models. The obtained results show that the effects of asphyxiant gases are more significant than those of irritant gases. The maximum FEC and FED values are greater than the critical threshold of 1, indicating the catastrophic toxicity in such fire scenarios. The minimum fresh air renewal rate required is computed to provide quantitative guides for ventilation management, firefighting and rescue. [ABSTRACT FROM AUTHOR]

Amongst the background of the popularization of the lithium-ion battery (LIB), the thermal issues have attracted a significant amount of attention. In the present paper, a novel integrated system is proposed with thermal management and rapid cooling based on C 6 F 12 O spray cooling in a closed loop. Through experiments using a 4 × 4 dummy 18650 cylindrical battery pack, the cooling performance of the battery thermal management system (BTMS) based on the C 6 F 12 O spray cooling is demonstrated to be effective. Further, the controllable heat generation benefits for the analysis of heat dissipation mechanisms. For the condition of 6 cm spray height with 2.05 g/s flow rate, the heat is taken away by the liquid film accounted for around 30% of the total heat dissipation, while that of direct spray cooling accounted for around 70%. In the rapid cooling experiment, compared with the blank experiment, the thermal runaway maximum temperature significantly decreased by 517.1 °C and the thermal runaway of the first battery is delayed by 229 s. Owing to the significantly effective heat removal ability of C 6 F 12 O spray cooling, the propagation of the thermal runaway is cut off. • A novel integrated system with thermal management and rapid cooling is proposed. • The effects of spray height, flow rate, and heat generation are explored. • The effectiveness of the proposed management system is proved experimentally. • The propagation of thermal runaway is cut off with the application of spray cooling. [ABSTRACT FROM AUTHOR]

The succinonitrile (SN) plastic crystal electrolyte with excellent comprehensive properties such as high room temperature (RT) ionic conductivity, wide electrochemical window and low cost, making it a promising candidate for RT solid-state lithium batteries (SSLBs). However, severe spontaneous chemical reactions between SN and active Li anode cause serious damage to the electrolyte/electrode interface, which still needs to be further improved. In this work, an in-situ polymerized SN-based composite solid-state electrolyte (CSE) is exploited to conquer the severe side-reactions between SN-based electrolyte and Li anode, the PALA0.5@-CSE (polyacrylonitrile (PAN): modified-Li l.3 Al 0.3 Ti l.7 (PO 4) 3 (LATP@) = 1:0.5, w/w) demonstrates an outstanding ionic conductivity (0.45 mS cm−1), high electrochemical stability (5.1 V) and improved Li+ transference number (0.67) at RT. The Li symmetric cells with PALA0.5@-CSE shows a high critical current density (CCD) of 1.2 mA cm−2, and the Li symmetric cells deliver excellent cycle stability over 500 h, demonstrating the superior ability of PALA0.5@-CSE to suppress the side-reactions between SN and Li anode and the rapid growth of Li dendrite. In Li||LiFePO 4 (LFP) full cell, the SSLBs provide excellent RT rate capability and stable cycling performance. Moreover, the PALA0.5@-CSE possesses high thermal stability and incombustibility, demonstrating its superior safety for the future utilization of SN-based SSLBs. The modification of LATP was effective at stabilizing the interface, the formed robust SEI film could alleviate the severe interfacial side reactions between SN and Li anode. [Display omitted] • High ionic conductivity (0.45 mS cm−1) and Li+ transference number (0.67) is achieved. • The robust SEI film effectively mitigates the uncontrollably parasitic side-reactions. • The PALA0.5@-CSE exhibits high thermal stability and nonflammable. • Solid-state SN-based lithium batteries show superior performances at room temperature. [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]

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]

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]

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]

• 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]

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]

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]

The vital physical and chemical properties of the lithium conducting salt, solvent/co-solvent and functional additive determine the overall properties and performance of the resulting electrolyte formulation. Explorations on right combinations of the carefully selected electrolyte components are expected to further balance the electrochemical and safety performances of chosen electrolyte formulations in given cell chemistries. In this study, a new nonaqueous aprotic electrolyte is designed by using lithium difluoro(oxalato)borate (LiODFB) as conducting salt, diethyl ethylphosphonate (DEEP) as solvent, and fluoroethylene carbonate (FEC) as co-solvent to achieve a nonflammable electrolyte formulation with competent electrochemical performance. The LiODFB and FEC are believed to take part in complex interfacial interactions with a synergistic effect. LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)‖Li cells using the optimized electrolyte formulation of 1.3 M LiODFB/DEEP 30% FEC exhibits a stable long-term cycling performance at 1.0 C with a reversible average specific discharge capacity of 169.5 mAh g−1 during 100 cycles, which is comparable to cells using commercial electrolytes. Furthermore, the 1.3 M LiODFB/DEEP 30% FEC electrolyte shows good thermal stability and effectively reduces the heat generation during thermal decomposition of NCM811 cathode. The results provide a good reference for the design of next generation of safe, nonflammable electrolytes for lithium-based battery application. • A nonflammable electrolyte with competent electrochemical performance is designed. • A stable and high-voltage cycling performance is realized for 100 cycles. • Heat generation of NCM811 decomposition is effectively reduced by DEEP electrolyte. [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]

• As the preload force increases, the safety vent opens earlier. • The battery expansion behavior has a mitigating effect on the gas pressure. • By constructing a TR hazard assessment model, the TR hazard is smallest at 3 kN. In electrochemical energy storage systems, large-format LiFePO 4 (LFP) batteries are usually formed the battery pack under preload force. However, the preload force effect on the safety of the batteries remains unclear. In this study, the TR and gas venting of the 280 Ah LFP batteries at 100% state of charge under four preload forces (0, 3, 6, and 9 kN) are investigated experimentally. The novelty compared to previous studies is that the fixture with a pressure sensor is used to set different preload forces before the experiment and monitor the expansion behavior of the LFP batteries during TR. The results quantitatively analyse the relationship between preload force and TR hazard of prismatic LFP battery. Two important results are presented: (I) the gas release inside LFP battery is horizontal and vertical at the same time, and the battery expansion behavior has a mitigating effect on gas pressure. (II) the TR hazard assessment model is pioneered to assess the TR hazard of batteries under four preload forces. The results show that the TR hazard is minimal at 3 kN. These results provide an effective guide to the setting of preload force and the emergency response to TR. [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]

Lithium-ion batteries are a promising technology for efficient energy conversion. Despite the significant advancements made in capacity and lifespan, a suitable battery thermal management system is necessary for more safety and reliability. The heat generation rate and core temperature are critical parameters for the design of the battery thermal management system and the monitoring signals for the battery management system, respectively. In consideration of said critical parameters, in the present paper, a novel algorithm for heat generation and core temperature is proposed based on single-temperature in-situ measurement of lithium-ion batteries. The in-situ measurement is ensured by introducing the calculation of the local equivalent convection heat transfer coefficient, and only obtaining the surface temperature. To verify the proposed method, cylindrical 5 Ah 26,700 lithium-ion batteries were used as test samples. The results of the experiment reveal that the error between the calculated core temperature and the measured core temperature was less than 4% during the entirety of the 2 C and 1.5C discharging processes. The efficacy and accuracy of the core temperature demonstrate that the proposed method could be a reliable tool in practice for battery thermal management and fault monitoring. • A novel in-situ estimation for heat generation and the core temperature is proposed. • Only the surface temperature is required in the algorithm. • The local equivalent convection heat transfer coefficient is derived. • The heat generation and the core temperature are obtained simultaneously. [ABSTRACT FROM AUTHOR]

[Display omitted] With increasingly more electrochemical energy storage systems installed, the safety issues of lithium batteries, such as fire explosions, have aroused greater concerns. In this study, the thermal runaway behaviors of two different structures of lithium–iron-phosphate battery packs were compared. A fire explosion occurred in battery pack I, which had a small venting area and void volume, but battery pack II with a large venting area and the void volume kept safe. To explain these phenomena, a new experimental method coupling multiple measurements was proposed in this study to survey the velocity, composition, and temperature of venting gas. The venting gas velocity had two peaks, with its maximum value reaching about 270 m/s. Besides, the venting gas was mainly composed of hydrogen and carbon dioxide, accounting for around 30.33% and 38.86%, respectively. With the experimental data used as boundary conditions in a mathematical model, the diffusion behaviors of the venting gas within these two battery packs were derived. By comparing the flammable gas concentration with their lower explosion limits and upper limits, this study found that the high concentration of hydrogen and ethylene might bear the main responsibility for the fire explosion in battery pack I. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries are widely used in electric vehicles to solve the problems of greenhouse gas emission. However, overcharging occurs due to the inconsistency of lithium-ion batteries, malfunction of charge control and inappropriate battery management. In order to solve the safety and cycle life problems of batteries suffering slight overcharging, quantitative analysis of the aging behavior, aging mechanisms and detection of slight overcharging cycling are studied in this manuscript. The results indicate that the cycle life of battery decreases linearly and exponentially with the upper cut-off voltage increasing when capacity and resistance are used as the threshold of the end of life respectively. The batteries have tolerance to slight overcharging with voltage lower than 4.6 V. The generated gas is not the main aging mechanism. Loss of active material is the main aging mechanism when the batteries are cycled at 4.4 V. Charging stress is the key factor triggering the loss of active material. The main aging mechanism becomes to be loss of lithium with the increase of voltage and cycle number due to the electrolyte oxidation, reduction and lithium plating. The differential voltage, coulombic efficiency and fast resistance increase are used as warming parameters of slight overcharging cycling. • Battery aging induced by slight overcharging cycling is analyzed quantitatively. • Slight overcharging influences power fading of battery more. • Lithium plating and electrolyte oxidation, reduction are the key factors of aging. • Warming parameters are extracted to detect slight overcharging cycling. [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]