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The most influential factor for self-ignition of high-pressure hydrogen is known to be the strength of the shock. Thus, the self-ignition can be suppressed by weakening the shock strength, which is possible by reducing the area where the hydrogen is ejected in this study. To confirm the possibility of this method, experiments were done by controlling the burst pressure of up to 302 bar and the ratio of the opening area. The experimental results showed that the minimum burst pressure of self-ignition is increased exponentially as the opening area is reduced. This confirmed that reducing the opening area under the same burst pressure conditions has an effect on the suppression of self-ignition. However, it was also found that the minimum shock speed that causes self-ignition gradually decreases as the opening area becomes smaller, which results from an increasing in mixing. The CFD simulation results showed that the volume of the flammable region in the tube was increased and the hydrogen-air mixing efficiency also increased when the opening area became smaller. The results suggest that reduction of the opening area can suppress a self-ignition by weakening the shock strength, but it should be noted that an increase in mixing effect also occurs.

Hydrogen storage in activated carbons (ACs) has proven to be a realistic alternative to compression and liquefaction. Adsorption capacities up to 5.8 wt% have indeed been obtained. The amount of adsorbed hydrogen depends on the textural properties of ACs, such as specific surface area and total pore volume. The modified Dubinin-Astakhov (MDA) equation proved to be a good analytical tool for describing hydrogen adsorption in a wide range of pressures and temperatures and for several adsorbents. The parameters of this model have been found to be somehow related to the textural properties of the adsorbent. Thus, we applied this model to understand better hydrogen adsorption on ACs over a wide range of pressures in relation to the textural properties of the ACs. We applied the MDA equation to evaluate also the isosteric heat of hydrogen adsorption, which was found to be in the range of 5–9 kJ mol−1. We compared the results obtained by applying the MDA equation with those obtained by both the sorption isosteric method and the Sips equation. This allowed finding the temperature dependence of the isosteric heat of adsorption, as well as its variation with respect to the textural properties of the ACs.

Hydrogen is efficient and environmentally friendly, but the danger of self-ignition resulted from the leakage of high-pressure hydrogen cannot be ignored. In this work, the self-ignition of high-pressure hydrogen released through different conditions was studied. 700-mm-length tubes with different diameters were adopted in our experiments. It summarized the characteristics of shock waves' attenuation and evolution process of hydrogen jets in tubes. In addition, effects of the boundary layer on the leading shock waves, the contact surface, and expansion waves were discussed. Results indicate that minimum pressure when self-ignition occurs for 15-mm-diameter tube is similar to 10-mm-diameter. And they have closely velocity of shock waves. Simulations show that the greater the release pressure, the more ignition products of hydrogen. Higher release pressure and smaller diameter can create a thicker boundary layer in micro shock tubes, and the boundary layer can lead to a change in the velocity of shock waves’ structures.

A series of experiments were conducted to study the pressure and combustion characteristics of the high-pressure hydrogen during the occurrence of spontaneous ignition and the conversion from spontaneous ignition to a jet fire and explosion. Different initial conditions including release pressure (4–10 MPa), tube diameter (10/15 mm), and tube length (0.3/0.7/1.2/1.7/2.2/3 m) were tested. The variation of the pressure and flame signal inside and outside of the tube and the development of the jet flame were recorded. The experimental results revealed that the minimum ignition pressure required for self-ignition of hydrogen at different tube diameters decreased first and then increased with the extension of tubes. The minimum ignition pressure for tubes diameters of 10 mm and 15 mm is no more than 4 MPa and the length of the tubes is L = 1.7 m. The minimum release pressure required for spontaneous ignition of a tube D = 15 mm is always lower than that of a tube D = 10 mm at the same tube length. When the spontaneous ignition occurred, it did not absolutely trigger the jet fire. The transition from spontaneous ignition to a jet fire must go through the specific stages.

The aim of this paper is to study the effect of the displacement rate on the fracture toughness under internal hydrogen of two different structural steels grades used in energy applications. To this end, steel specimens were pre-charged with gaseous hydrogen at 19.5 MPa and 450 °C for 21 h and then fracture toughness tests were carried out in air at room temperature. Permeation experiments were also conducted to obtain the hydrogen diffusion coefficients of the steels. It was observed that the lower the displacement rate and the higher the steel yield strength, the stronger the reduction in fracture toughness due to the presence of internal hydrogen. A change in the fracture micromechanism was also detected. All these findings were justified in terms of hydrogen diffusion and accumulation in the crack front region in the different steel specimens.

In the study presented here, an apparatus that correctly measured pressure–composition isotherms (PCi) at high pressures (up to 100 MPa) and temperatures (up to 200 °C) was developed. The PCi characteristics of a vanadium–titanium–chromium alloy at high pressure and temperature were examined with the apparatus to develop a metal hydride (MH) compressor. It was revealed that it is possible to use a 40 V 20Ti 40Cr (at%) alloy with a heat source below 200 °C for hydrogen compression in the approximate range of 2.1–30.0 MPa. The compressed content reached approximately 1.8 wt%, which is almost the same as the reversible hydrogen capacity at 20 °C.

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% H2) 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.

The fatigue limit properties of a carbon steel and a low-alloy Cr Mo steel were investigated via fully-reversed tension-compression tests, using smooth specimens in air and in 115-MPa hydrogen gas. With respect to the Cr Mo steel, specimens with sharp notches were also tested in order to investigate the threshold behavior of small cracks. The obtained S N data inferred that the fatigue limit was not negatively affected by hydrogen in either of the steels. Observation of fatigue cracks in the unbroken specimens revealed that non-propagating cracks can exist even in 115-MPa hydrogen gas, and that the crack growth threshold is not degraded by hydrogen. The experimental results provide justification for the fatigue limit design of components that are to be exposed to high-pressure hydrogen gas.

This paper describes experimental and numerical modelling results from an investigation into the flammability profiles associated with high pressure hydrogen jets released in close proximity to surfaces. This work was performed under a Transnational Access Agreement activity funded by the European Research Infrastructure project, H2FC. The experimental programme involved ignited and unignited releases of hydrogen at pressures of 150 and 425 barg through nozzles of 1.06 and 0.64 mm respectively. The proximity of the release to a ceiling or the ground was varied and the results compared with an equivalent free-jet test. During the unignited experiments concentration profiles were measured using hydrogen sensors. During the ignited releases thermal radiation was measured using radiometers and an infra-red camera. The results show that the flammable volume and flame length increase when the release is in close proximity to a surface. The increases are quantified and the safety implications discussed. Selected experiments were modelled using the CFD model FLACS for validation purposes and a comparison of the results is also included in this paper. Similarly to experiments, the CFD results show an increase in flammable volume when the release is close to a surface. The unstable atmospheric conditions during the experiments are shown to have a significant impact on the results.

A new non-destructive evaluation technique to detect cracks emanating from the inner surface (inner cracks) of a high-pressure hydrogen storage cylinder was developed by means of mechanoluminescence (ML) sensor consisting of SrAl2O4:Eu ML material and epoxy resin. To visualize the inner crack, a sheet ML sensor was attached onto the outer surface of the storage cylinder subjected to hydraulic pressure cycling with the maximum pressure of 45 MPa. The ML pattern was changed with an increase in the cycle number and the ML sensor could visualize the inner crack. The stress analysis by the finite element method clarified that the ML sensor provided unique equivalent strain distribution associated with stress concentration at the crack tip, i.e. the distance between two points having high equivalent strains was inversely proportional to the crack depth; consequently, the growth behavior of the inner crack was non-destructively quantified with the ML sensor attached on the outer surface.

The damage model described in [12] is used to predict the burst pressure and the burst mode of type IV hyperbaric tanks for hydrogen storage. The shape of the composite shell (as well as the fibre orientation at each point) ensuring the mechanical strength comes from the plug-in Wound Composite Modeler. The FE simulations are found not only to predict the global behaviour of the vessel (radial and axial displacement when undergoing an increasing inner pressure, burst pressure value), but also the damage modes at the ply scale. Thus, they are capable of explaining phenomena such as the non linearity due to the presence of a gap between the liner and the composite shell or the possible leaks due to delamination in the dome and providing the strain level in each composite layer.

Vehicle fires may cause localized fires on on-board high-pressure hydrogen storage tanks. To verify the safety performance of such tanks under localized fire exposure, a localized fire test was proposed in the Global Technical Regulation for Hydrogen Fuel Cell Vehicles. However, practicality and validity of the proposed test still require further verification. In this paper, this new fire test was experimentally investigated using the type 3 tanks. Influences of hydrogen and air as the filling media were studied. A three-dimensional computational fluid dynamics model was developed to analyze the effects of filling pressure and localized fire exposure time on the activation of thermally-activated pressure relief device (TPRD). The experimental results showed that temperature distribution on the tank surface was uneven around the circumference. The rising temperature of internal hydrogen or air contributed little to TPRD activation. The simulation results indicated that TPRD activation time was slightly affected by the variations of the filling pressures, but it increased when the localized fire exposure time was extended.

Hydrogen absorption/desorption properties of La(0.2)Y(0.8)Ni(5-x)Mn(x) (x = 0.2, 0.3, 0.4) alloys for high-pressure hydrogen compression application were investigated systematically. The Pressure Composition isotherms and absorption kinetics were measured at 293, 303 and 313 K by the volumetric method. XRD analyses showed that all the investigated alloys presented CaCu(5) type hexagonal structure and the unit cell volume increased in both a and c lattice axes with Mn substitution. Hydrogen absorption/desorption measurements revealed that Mn could lower the plateau pressure effectively, improve the hydrogen storage capacity and absorption kinetics but slightly increase the slope of the pressure plateau and hysteresis. The study results suggest that La(0.2)Y(0.8)Ni(4.8)Mn(0.2) is suitable for the high-pressure stage compression of the hydrogen compressor and the other two alloys, La(0.2)Y(0.8)Ni(4.7)Mn(0.3) and La(0.2)Y(0.8)Ni(4.6)Mn(0.4), for the preliminary stage. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Abstact The bonfire test is an important prototype test in the standard of hydrogen storage vessels. It is designed to demonstrate the safety performance of the vessel and the Pressure Relief Devices (PRD) under a specified fire condition. However, the required temperature of the thermocouples, which is one of the most relevant parameters, is still not unified. The fuel types and fuel flow, which may influence on the temperature distribution and the PRD activation time, are also not specified in the standards. In this paper, an experiment was carried out on a composite vessel filled with hydrogen and the experimental results of temperature and pressure were obtained. A 3D simulation model was developed to study the bonfire test. The effects of fuel type, fuel flow and filling medium on the temperature rising of internal gas were studied. It reveals that the influence of fuel type on the temperature rising is significant. In addition, the rate of temperature rising increases as the fuel flow increases. However, the filling medium has little effect on the temperature rising.

By combining the micromechanics and continuum damage mechanics, a theoretical model is proposed to perform the fatigue evaluation of high pressure hydrogen storage vessel under cyclic internal pressure, which concentrates on the fatigue properties of the aluminum liner. Results show that the fatigue lifetime of vessel relates to the finite element mesh size, crack density and ratio in an element, cyclic loading amplitude and stress status at the liner. Effects of the mesh size and crack density on the fatigue lifetime of vessel are discussed. In addition, numerical results are also compared with those by experiments.

Over the last century, there have been reports of high pressure hydrogen leaks igniting for no apparent reason, and several ignition mechanisms have been proposed. Although many leaks have ignited, there are also reported leaks where no ignition has occurred. Investigations of ignitions where no apparent ignition source was present have often been superficial, with a mechanism postulated which, whilst appearing to satisfy the conditions prevailing at the time of the release, simply does not stand up to rigorous scientific analysis. Some of these proposed mechanisms have been simulated in a laboratory under superficially identical conditions and appear to be rigorous and scientific, but the simulated conditions often do not have the same large release rates or quantities, mainly because of physical constraints of a laboratory. Also, some of the release scenarios carried out or simulated in laboratories are totally divorced from the realistic situation of most actual leaks. Clearly there are gaps in the knowledge of the exact ignition mechanism for releases of hydrogen, particularly at the high pressures likely to be involved in future storage and use. Mechanisms which have been proposed in the past are the reverse Joule–Thomson effect, electrostatic charge generation, diffusion ignition, sudden adiabatic compression, and hot surface ignition. Of these, some have been characterised by means of computer simulation rather than by actual experiment, and hence are not validated. Consequently there are discrepancies between the theories, releases known to have ignited, and releases which are known to have not ignited. From this, postulated ignition mechanisms which are worthy of further study have been identified, and the gaps in information have been highlighted. As a result, the direction for future research into the potential for ignition of hydrogen escapes has been identified.

For the low alloyed fine grained ferritic structural steel 15 MnNi 6 3 in a first step J-integral tests were performed at room temperature in argon, pure high pressure hydrogen gas as well as with admixtures of oxygen (10 vpm, 150 vpm) in the single specimen technique. The JR-curve received for pure hydrogen environment is essentially lower than the curve for argon. The JR-curve for hydrogen with 10 vpm oxygen is shifted towards the one for pure hydrogen whereas the admixture of 150 vpm oxygen results in a JR-curve near the argon curve. The JIc-value for 10 vpm oxygen admixture is approximately twice the one for pure hydrogen, for 150 vpm oxygen admixture about three times that for pure hydrogen. For the specimen fractured in argon a dimpled fracture surface, for the one tested in pure hydrogen a flat quasi-cleavage fracture was observed. With increasing oxygen admixture the portion of ductile fracture grows.

Many common structural alloys are subject to gross embrittlement by hydrogen. Since hydrogen-induced fracture in such cases can result in catastrophic failures of equipment, it is very important to consider appropriate design measures and alternative materials choices for hydrogen service. There are two areas of concern for hydrogen energy applications: systems to generate hydrogen or hydrogen-bearing gases at high temperatures and pressures, and high pressure hydrogen transmission and storage systems. It appears possible in each area to identify the desirable classes of structural materials for hydrogen service.

The influence of high purity hydrogen gas of 9 MPa on the ductility of a normalized steel 15 MnNi 6 3 and of a thermomechanically treated steel X 56 TM was investigated at room temperature by tensile tests with constant extension rate for smooth specimens. For both steels a remarkable decrease of reduction of area due to hydrogen was found. The change in fracture mode from dimple fracture in air to quasi cleavage fracture in hydrogen was revealed by fractography. Further constant extension rate tests on specimens with circumferential notches demonstrate the detrimental effect of notches on the amount of ductility in the presence of hydrogen.