Japan

Reversible solid oxide cells (r-SOCs) can be operated in either solid oxide fuel cell or solid oxide electrolysis cell mode. They are expected to become important in the support of renewable energy due to their high efficiency for both power generation and hydrogen generation. The exchange current density is one of the most important parameters in the quantification of electrode performance in solid oxide cells. In this study four different fuel electrodes and two different air electrodes are fabricated using different materials and the microstructures are compared. The temperature fuel humidification and oxygen concentration at the air electrode are varied to obtain the apparent exchange current density for the different electrode materials. In contrast to ruthenium-and-gadolinia-doped ceria (Rh-GDC) as well as nickel-and-gadolinia-doped ceria (Ni-GDC) electrodes significant differences in the apparent exchange current density were observed between electrolysis and fuel cell modes for the nickel-scandia-stabilized zirconia (Ni-ScSZ) cermet. Variation of gas concentration revealed that surface adsorption sites were almost completely vacant for all these electrodes. The apparent exchange current densities obtained in this study are useful as a parameter for simulation of the internal properties of r-SOCs.

It is necessary to investigate cylinder crush behavior for improvement of fuel cell vehicle crash safety. However there have been few crushing behaviour investigations of high pressurized cylinders subjected to external force. We conducted a compression test of pressurized cylinders impacted by external force. We also investigated the cylinder strength and crushing behaviour of the cylinder. The following results were obtained.

• The crush force of high pressurized cylinders is different from the direction of external force. The lateral crush force of high pressurized cylinders is larger than the external axial crush force.
• Tensile stress occurs in the boundary area between the cylinder dome and central portion when the pressurized cylinder is subjected to axial compression force and the cylinder is destroyed.
• However the high pressurized cylinders tested had a high crush force which exceeded the assumed range of vehicle crash test procedures

For the evaluation of hydrogen and fuel cell vehicle safety a new comprehensive facility was constructed in our institute. The new facility includes an explosion resistant indoor vehicle fire test building and high pressure hydrogen tank safety evaluation equipment. The indoor vehicle fire test building has sufficient strength to withstand even an explosion of a high pressure hydrogen tank of 260 liter capacity and 70 MPa pressure. It also has enough space to observe vehicle fire flames of not only hydrogen but also other conventional fuels such as gasoline or compressed natural gas. The inside dimensions of the building are a 16 meter height and 18 meter diameter. The walls are made of 1.2 meter thick reinforced concrete covered at the insides with steel plate. This paper shows examples of hydrogen vehicle fires compared with other fuel fires and hydrogen high pressure tank fire tests utilizing several kinds of fire sources. Another facility for evaluation of high pressure hydrogen tank safety includes a 110 MPa hydrogen compressor with a capacity of 200 Nm3/h a 300 MPa hydraulic compressor for burst tests of 70 MPa and higher pressure tanks and so on. This facility will be used for not only the safety evaluation of hydrogen and fuel cell vehicles but also the establishment of domestic/international regulations codes and standards.

This study investigated a pre-cooled turbojet engine for a Mach 5 class hypersonic transport aircraft. The engine was demonstrated under takeoff and Mach 2 flight conditions and a Mach 5 propulsion wind tunnel test is planned. The engine is composed of a pre-cooler a core engine and an afterburner. The engine was tested under simulated Mach 4 conditions using an air supply facility. High-temperature air under high pressure was supplied to the engine components through an airflow control valve and an orifice flow meter and liquid hydrogen was supplied to the pre-cooler and the core engine. The results confirmed that the starting sequence of the engine components was effective under simulated Mach 4 conditions using liquid hydrogen fuel. The pre-cooling effect caused no damage to the rotating parts of the core engine in the experiment.

Hydrogen is one of the important alternative fuels for future transportation. At the present stage research into hydrogen safety and designing risk mitigation measures are significant task. For compact storage of hydrogen in fuel cell vehicles storage of hydrogen under high pressure up to 40 MPa at refuelling stations is planned and safety in handling such high-pressure hydrogen is essential. This paper describes our experimental investigation into dispersion of high-pressure hydrogen gas which leaks through pinholes in the piping to the atmosphere. First in order to comprehend the basic behaviour of the steady dispersion of high-pressure hydrogen gas from the pinholes the time-averaged concentrations were measured. In our experiments initial release pressures of hydrogen gas were set at 20 MPa or 40 MPa and release diameters were in the range from 0.25 mm to 2 mm. The experimental results show that the hydrogen concentration along the axis of the dispersion plume can be expressed as a simple formula which is a function of the downwind distance X and the equivalent release diameter. This formula enables us to easily estimate the axial concentration (maximum concentration) at each downstream distance. However in order for the safety of flammable gas dispersion to be analyzed comparisons between time-averaged concentrations evaluated as above and lower flammable limit are insufficient. This is because even if time-averaged concentration is lower than the flammability limit instantaneous concentrations fluctuate and a higher instantaneous concentration occasionally appears due to turbulence. Therefore the time-averaged concentration value which can be used as a threshold for assessing safety must be determined considering concentration fluctuations. Once the threshold value is determined the safe distance from the leakage point can be evaluated by the above-mentioned simple formula. To clarify the phenomenon of concentration fluctuations instantaneous concentrations were measured with the fast-response flame ionization detector. A small amount of methane gas was mixed into the hydrogen as a tracer gas for this measurement. The relationship between the time-mean concentration and the occurrence probability of flammable concentration was analyzed. Under the same conditions spark-ignition experiments were also conducted and the relationship between the occurrence probability of flammable concentration and actual ignition probabilities were also investigated. The experimental results show that there is a clear correlation between the time-mean concentration the occurrence probability of flammable concentration flame length and occurrence probability of hydrogen flame.

To identify the safety issues associated with hydrogen fuelling stations incidents at such stations in Japan and the USA were analyzed considering the regulations in these countries. Leakage due to the damage and fracture of main bodies of apparatuses and pipes in Japan and the USA is mainly caused by design error that is poorly planned fatigue. Considering the present incidents in these countries adequate consideration of the usage environment in the design is very important. Leakage from flanges valves and seals in Japan is mainly caused by screw joints. If welded joints are to be used in hydrogen fuelling stations in Japan strength data for welded parts should be obtained and pipe thicknesses should be reduced. Leakage due to other factors e.g. external impact in Japan and the USA is mainly caused by human error. To realize self-serviced hydrogen fuelling stations safety measures should be developed to prevent human error by fuel cell vehicle users.

This paper shows the numerical investigation on the self-ignition behavior of high pressure hydrogen released from the tube. The present study aims to clarify the effect of parameters on the behavior and duration of self-ignition outside the tube using two-dimensional axisymmetric numerical simulation with detailed chemistry. The parameters in this study are release pressure tube diameter and tube length. The strength of the spherical shock wave to keep chemical reaction and expansion are important factors for self ignited hydrogen jet to be sustained outside the tube. The trend of strength of spherical shock wave is enhanced by higher release pressure and larger tube diameter. The chemical reaction weakens due to expansion and the degree of expansion becomes larger as the spherical shock wave propagates. The characteristic time for the chemical reaction becomes shorter in higher release pressure larger tube diameter and longer tube diameter cases from the induction time under constant volume assumption. The self ignited hydrogen jet released from the tube is sustained up to the distance where the characteristic time for chemical reaction is shorter than the characteristic time for the flow to expand and higher release pressure larger tube diameter and longer tube length expand the distance where the tip flame can propagate downstream. For the seed flame which is the key for jet fire the larger amount of the ignited volume when the shock wave reaches the tube exit contributes to the formation and stability of the seed flame. The amount of the ignited volume tends to be larger in the longer tube length higher release pressure and larger tube diameter cases.

Although many studies have looked at safety issues relating to hydrogen fuelling stations few studies have analyzed the security risks such as deliberate attack of the station by threats such as terrorists and disgruntled employees. The purpose of this study is to analyze security risks for a hydrogen fuelling station with an on-site production of hydrogen from methylcyclohexane. We qualitatively conducted a security risk analysis using American Petroleum Institute Standard 780 as a reference for the analysis. The analysis identified 93 scenarios including pool fires. We quantitatively simulated a pool fire scenario unique to the station to analyze attack consequences. Based on the analysis and the simulation we recommend countermeasures to prevent and mitigate deliberate attacks.

The hydrogen permeation coefficient (ϕ) is generally used as a measure to show hydrogen permeation ability through dense metallic membranes which is the product of the Fick’s diffusion coefficient (D) and the Sieverts’ solubility constant (K). However the hydrogen permeability of metal membranes cannot be analyzed consistently with this conventional description. In this paper various methods for consistent analysis of hydrogen permeability are reviewed. The derivations of the descriptions are explained in detail and four applications of the consistent descriptions of hydrogen permeability are introduced: (1) prediction of hydrogen flux under given conditions (2) comparability of hydrogen permeability (3) understanding of the anomalous temperature dependence of hydrogen permeability of Pd-Ag alloy membrane and (4) design of alloy composition of non-Pd-based alloy membranes to satisfy both high hydrogen permeability together with strong resistance to hydrogen embrittlement.

This paper addresses from both macro- and micro- areal coverage in introducing hydrogen system in terms of cost and performance where the produced hydrogen from surplus photovoltaic (PV) power is stored. Feed-in tariff in Japan had successful achievement for great expansion of renewable energy systems (RES) causing problematic operation due to excess power by overcapacity of RES. One of the candidate approaches to overcome this surplus energy by RES is Power to gas (P2G) system using electrolysis cells (ECs) fuel cells (FCs) or co-firing in gas turbines both for energy conversion as well as power balancing. Numerous studies had been investigated on P2G however within our knowledge no study had been addressed the system from both coverages with different capacity and scales. We investigate micro level (zero emission building in our university) and macro level (Kyushu one of big regions in Japan). We describe for macro side preliminary result on economic analysis of using surplus power of RES via production and storage of hydrogen while for micro side research design.

Ductile cast iron (DCI) is one of prospective materials used for the hydrogen equipment because of low-cost good workability and formability. The wide range of mechanical properties of DCI is obtained by controlling microstructural factors such as graphite size volume fraction of graphite matrix structure and so on. Therefore it is important to find out an optimal microstructural condition that is less susceptible to hydrogen embrittlement. In this study the effects of graphite size on the hydrogen absorption capability and the hydrogen-induced ductility loss of ferritic DCI were investigated.<br/>Several kinds of ferritic DCIs with a different graphite diameter of about 10 µm - 30 µm were used for the tensile test and the hydrogen content measurement. Hydrogen charging was performed prior to the tensile test by exposing a specimen to high-pressure hydrogen gas. Then the tensile test was performed in air at room temperature. The hydrogen content of a specimen was measured by a thermal desorption analyzer.<br/>It was found that the amount of hydrogen stored in DCI was dependent on the graphite size. As the graphite diameter increased the hydrogen content sharply increased at a certain graphite diameter and then it became nearly constant irrespective of increase in graphite diameter. In other words there was the critical graphite diameter that significantly changed the hydrogen absorption capability. The ductility was decreased by hydrogen and the hydrogen-induced ductility loss was dependent on the hydrogen content. Therefore the hydrogen embrittlement of DCI became remarkable when the graphite size was larger than the critical value.

The states of Regulations Codes and Standards (RCS) of hydrogen refueling stations (HRSs) in Japan and France are compared and specified items to understand correspondence and differences among each RCSs for realizing harmonization in RCS. Japan has been trying to reform its RCSs to reduce HRS installation and operation costs as a governmental target. Specific crucial regulatory items such as safety distances mitigation means materials for hydrogen storage and certification of anti-explosion proof equipments are compared in order to identify the origins of the current obstacles for disseminating HRS.

Hydrogen leakage in a closed space is one of the causes of serious accidents because of its high detonability. Assuming the situation that hydrogen is accumulated in a closed space two-dimensional numerical simulation for hydrogen oxygen detonation which propagates in stratified fuel and oxidizer with concentration gradient is conducted by using detailed chemical reaction model. The concentration gradient between fuel and oxidizer is expressed by changing the number of hydrogen moles by using sigmoid function. Strength of discontinuity at the boundary is controlled by changing the gain of the function. The maximum pressure history shows that the behaviour of triple points is different depending on the strength of discontinuity between the two kind of gas. In without concentration gradient case the transverse waves are reflected at the boundary because of the sudden change of acoustic impedance ratio between two kind of gas. In contrast in with concentration gradient case the transverse wavs are not reflected in the buffer zone and they are flowed into the oxidizer as its structures are kept. As a result the confined effect declines as the strength of discontinuity between the two kind of gas is weakened and the propagating distance of detonation changes

Hydrogen has emerged as an important part of the clean energy mix needed to ensure a sustainable future. Falling costs for hydrogen produced with renewable energy combined with the urgency of cutting greenhouse-gas emissions has given clean hydrogen unprecedented political and business momentum.



This paper from the International Renewable Energy Agency (IRENA) examines the potential of hydrogen fuel for hard-to-decarbonise energy uses including energy-intensive industries trucks aviation shipping and heating applications. But the decarbonisation impact depends on how hydrogen is produced. Current and future sourcing options can be divided into grey (fossil fuel-based) blue (fossil fuel-based production with carbon capture utilisation and storage) and green (renewables-based) hydrogen. Green hydrogen produced through renewable-powered electrolysis is projected to grow rapidly in the coming years.



Among other findings:



Important synergies exist between hydrogen and renewable energy. Hydrogen can boost renewable electricity market growth and broaden the reach of renewable solutions.

• Electrolysers can add demand-side flexibility. In advanced European energy markets electrolysers are growing from megawatt to gigawatt scale.
• Blue hydrogen is not inherently carbon free. This type of production requires carbon-dioxide (CO2) monitoring verification and certification.
• Synergies may exist between green and blue hydrogen deployment given the chance for economies of scale in hydrogen use or logistics.
• A hydrogen-based energy transition will not happen overnight. Hydrogen use is likely to catch on for specific target applications. The need for new supply infrastructure could limit hydrogen use to countries adopting this strategy.
• Dedicated hydrogen pipelines have existed for decades and could be refurbished along with existing gas pipelines. The implications of replacing gas abruptly or changing mixtures gradually should be further explored.

Trade of energy-intensive commodities produced with hydrogen including “e-fuels” could spur faster uptake or renewables and bring wider economic benefits.

Multiple-energy-fuelling stations which can supply several types of energy such as gasoline CNG and hydrogen could guarantee the efficient use of space. To guide the safety management of hybrid hydrogen–gasoline fuelling stations which utilize liquid hydrogen as an energy carrier the scale of gasoline pool fires was estimated using the hazard assessment tool Toxic Release Analysis of Chemical Emissions (TRACE). Subsequently the temperature and the stress due to temperature distribution were estimated using ANSYS. Based on the results the safety of liquid hydrogen storage tanks was discussed. It was inferred that the emissivity of the outer material of the tank and the safety distance between liquid hydrogen storage tanks and gasoline dispensers should be less than 0.2 and more than 8.5 m respectively to protect the liquid hydrogen storage tank from the gasoline pool fire. To reduce the safety distance several measures are required e.g. additional thermal shields such as protective intumescent paint and water sprinkler systems and an increased slope to lead gasoline off to a safe domain away from the liquid hydrogen storage tank

Hydrogen intrudes into the steel during pickling process which is a pre-processing before a joining process promoting crack formation. In a mechanical clinching which is one of joining method in the automotive industry cracks due to large strain sometimes forms. In order to guarantee reliability it is important to clarify the influence of hydrogen on crack formation of the joint. In this study we clarified the influence of hydrogen for the crack formation on the mechanical clinching. Hydrogen charge was carried out using an electrolytic cathode charge. After the charging mechanical clinching was performed. Mechanical clinching was carried out with steel plate and aluminium alloy plate. To clarify the influence of hydrogen mechanical clinching was conducted without hydrogen charring. To investigate the crack formation the test piece was cut and the cut surface was observed. When the joint was broken during the clinching the fracture surface was observed using an optical microscope and an electron microscope. The load-displacement diagram showed that without hydrogen charging the compressive load increased as the displacement increased. On the other hand the compressive load temporarily decreased with high hydrogen charging suggesting that cracks formed at the time. The cut surface observation showed that interlock was formed in both cases with low hydrogen charging and without hydrogen charging. With low hydrogen charging no cracks were formed in the joint. When high hydrogen charging was performed cracks were formed at the joining point. Fracture analysis showed brittle-like fracture surface. These results indicate that hydrogen induces crack formation in the mechanical clinching.

Effects of hydrogen on slow-strain-rate tensile (SSRT) and fatigue-life properties of 17-4PH H1150 martensitic stainless steel having an ultimate tensile strength of ~1GPa were investigated. Smooth and circumferentially-notched axisymmetric specimens were used for the SSRT and fatigue-life tests respectively. The fatigue-life tests were done to investigate the hydrogen effect on fatigue crack growth (FCG) properties. The specimens tested in air at ambient temperature were precharged by exposure to hydrogen gas at pressures of 35 and 100 MPa at 270°C for 200 h. The SSRT properties of the H-charged specimens were degraded by hydrogen showing a relative reduction in area (RRA) of 0.31 accompanied by mixed fracture surfaces composed of quasi-cleavage (QC) and intergranular cracking (IG). The fatigue-life tests conducted under wide test frequencies ranging from 10-3 Hz to 10 Hz revealed three distinct characteristics in low- and high-cycle regimes and at the fatigue limit. The fatigue limit was not degraded by hydrogen. In the high-cycle regime the hydrogen caused FCG acceleration with an upper bound ratio of 30 accompanied by QC surfaces. In the low-cycle regime the hydrogen caused FCG acceleration with a ratio of ~100 accompanied by QC and IG. The ordinary models such as process competition and superposition models hardly predicted the H-assisted FCG acceleration; therefore an interaction model successfully reproducing the experimental FCG acceleration was newly introduced.

The presented research focuses on an optimization design of a catalyst distribution inside a small-scale methane/steam reforming reactor. A genetic algorithm was used for the multiobjective optimization which included the search for an optimum of methane conversion rate and a minimum of the difference between highest and lowest temperatures in the reactor. For the sake of computational time the maximal number of the segment with different catalyst densities was set to be thirty in this study. During the entire optimization process every part of the reactor could be filled either with a catalyst material or non-catalytic metallic foam. In both cases the porosity and pore size was also specified. The impact of the porosity and pore size on the active reaction surface and permeability was incorporated using graph theory and three-dimensional digital material representation. Calculations start with the generation of a random set of possible reactors each with a different catalyst distribution. The algorithm calls reforming simulation over each of the reactors and after obtaining concentration and temperature fields the algorithms calculated fitness function. The properties of the best reactors are combined to generate a new population of solutions. The procedure is repeated and after meeting the coverage criteria the optimal catalyst distribution was proposed. The paper is summarized with the optimal catalyst distribution for the given size and working conditions of the system.

In this paper a multifunctional energy system (MES) is proposed for recovering energy from the extra of coke oven gas (COG) which is usually flared or vented out as a waste stream in coke making plants. The proposed system consists of a pressure swing adsorption (PSA) unit for extracting some of the hydrogen from COG a gas turbine for producing heat and power from PSA offgas and a heat recovery steam generator (HRSG) for generating the steam required by the plant's processes. o assess the performance of the system practically simulations are carried out on the basis of the design and operational conditions of Zarand Coke Making Plant in Iran. The results indicate that by utilizing about 4.39 tons of COG per hour 6.5 MW of net electric power can be approximately produced by the gas turbine which can supply the coke making plant's total electrical power demand. Furthermore through recovering heat from gas turbine's exhaust close to 57% of the plant's steam demand can be supplied by the HRSG unit. It is also found that around 350 kilograms per hour of nearly pure hydrogen (99.9% purity) at 200 bar can be produced by the PSA unit. According to the sensitivity analysis results if the hydrogen content of the coke oven gas decreases by about 10% the gross power output of the gas turbine also declines by around 5.2% due to the reduction of LHV of the PSA offgas. Moreover economic evaluation of the system shows that the payback period of the investment which is estimated at 36.1 M$ is about 5.5 years. The net present value (NPV) and internal rate of return on investment (ROI) are calculated to be 17.6% and 43.3 M$ respectively.

Hydrogen is a promising energy carrier in the clean energy systems currently being developed. However its effectiveness in mitigating greenhouse gas (GHG) emissions requires conducting a lifecycle analysis of the process by which hydrogen is produced and supplied. This study focuses on the hydrogen for the transport sector in particular renewable hydrogen that is produced from wind- or solar PV-powered electrolysis. A life cycle inventory analysis is conducted to evaluate the Well-to-Tank (WtT) GHG emissions from various renewable hydrogen supply chains. The stages of the supply chains include hydrogen being produced overseas converted into a transportable hydrogen carrier (liquid hydrogen or methylcyclohexane) imported to Japan by sea distributed to hydrogen filling stations restored from the hydrogen carrier to hydrogen and filled into fuel cell vehicles. For comparison an analysis is also carried out with hydrogen produced by steam reforming of natural gas. Foreground data related to the hydrogen supply chains are collected by literature surveys and the Japanese life cycle inventory database is used as the background data. The analysis results indicate that some of renewable hydrogen supply chains using liquid hydrogen exhibited significantly lower WtT GHG emissions than those of a supply chain of hydrogen produced by reforming of natural gas. A significant piece of the work is to consider the impacts of variations in the energy and material inputs by performing a probabilistic uncertainty analysis. This suggests that the production of renewable hydrogen its liquefaction the dehydrogenation of methylcyclohexane and the compression of hydrogen at the filling station are the GHG-intensive stages in the target supply chains.

Energies based on biomaterials attract a lot of interest as next-generation energy because biomaterials are environmentally friendly materials and abundant in nature. Fuel cells are also known as the clean and important next-generation source of energy. In the present study to develop the fuel cell based on biomaterials a novel biofuel cell which consists of collagen electrolyte and the hydrogen fuel generated from photochemical system II (PSII) in photosynthesis has been fabricated and its property has been investigated. It was found that the PSII solution in which PSII was extracted from the thylakoid membrane using a surfactant generates hydrogen by the irradiation of light. The typical hydrogen-generating rate is approximately 7.41 × 1014 molecules/s for the light intensity of 0.5 mW/cm2 for the PSII solution of 5 mL. The biofuel cell using the PSII solution as the fuel exhibited approximately 0.12 mW/cm2 . This result indicates that the fuel cell using the collagen electrolyte and the hydrogen fuel generated from PSII solution becomes the new type of biofuel cell and will lead to the development of the next-generation energy

The utilization of hydrogen energy is important for achieving a low-carbon society. Japan has set ambitious goals for hydrogen stations and fuel cell vehicles focusing on the introduction and dissemination of self-refuelling systems. This paper evaluates public trust in the fuel equipment and self-handling technology related to self-refuelling hydrogen stations and compares it with that for widespread gasoline stations. To this end the results of an online survey of 300 people with Japanese driver licenses are reported and analyzed. The results show that trust in the equipment and self-handling is more important for the user than trust in the fuel. In addition to introduce and disseminate new technology such as hydrogen stations users must be made aware of the risk of using the technology until it becomes as familiar as existing gasoline station technology.

To understand hydrogen uptake in porous carbon materials we developed machine learning models to predict excess uptake at 77 K based on the textural and chemical properties of carbon using a dataset containing 68 different samples and 1745 data points. Random forest is selected due to its high performance (R² > 0.9) and analysis is performed using Shapley Additive Explanations (SHAP). It is found that pressure and Brunauer-Emmett-Teller (BET) surface area are the two strongest predictors of excess hydrogen uptake. Surprisingly this is followed by a positive correlation with oxygen content contributing up to ∼0.6 wt% additional hydrogen uptake contradicting the conclusions of previous studies. Finally pore volume has the smallest effect. The pore size distribution is also found to be important since ultramicropores (dp < 0.7 nm) are found to be more positively correlated with excess uptake than micropores (d_p < 2 nm). However this effect is quite small compared to the role of BET surface area and total pore volume. The novel approach taken here can provide important insights in the rational design of carbon materials for hydrogen storage applications.

Hydrogen fuel cell vehicles are expected to play an important role in the future and thus have improved significantly over the past years. Hydrogen fuel cell motorcycles with a small container for compressed hydrogen gas have been developed in Japan along with related regulations. As a result national regulations have been established in Japan after discussions with Japanese motorcycle companies stakeholders and experts. The concept of Japanese regulations was proposed internationally and a new international regulation on hydrogen-fueled motorcycles incorporating compressed hydrogen storage systems based on this concept are also established as United Nations Regulation No. 146. In this paper several technical regulations on hydrogen safety specific to fuel cell motorcycles incorporating compressed hydrogen storage systems are summarized. The unique characteristics of these motorcycles e.g. small body light weight and tendency to overturn easily are considered in these regulations.

In order for fuel cell vehicles to develop a widespread role in society it is essential that hydrogen refuelling stations become established. For this to happen there is a need to demonstrate the safety of the refuelling stations. The work described in this paper was carried out to provide experimental information on hydrogen outflow dispersion and explosion behaviour. In the first phase homogeneous hydrogen-air-mixtures of a known concentration were introduced into an explosion chamber and the resulting flame speed and overpressures were measured. Hydrogen concentration was the dominant factor influencing the flame speed and overpressure. Secondly high-pressure hydrogen releases were initiated in a storage room to study the accumulation of hydrogen. For a steady release with a constant driving pressure the hydrogen concentration varied as the inlet airflow changed depending on the ventilation area of the room the external wind conditions and also the buoyancy induced flows generated by the accumulating hydrogen. Having obtained this basic data the realistic dispersion and explosion experiments were executed at full-scale in the hydrogen station model. High-pressure hydrogen was released from 0.8-8.0mm nozzle at the dispenser position and inside the storage room in the full-scale model of the refuelling station. Also the hydrogen releases were ignited to study the overpressures that can be generated by such releases. The results showed that overpressures that were generated following releases at the dispenser location had a clear correlation with the time of ignition distance from ignition point.

According to the Global technical regulation on hydrogen and fuel cell vehicles (FCV) fuel cell discharge system at the vehicle exhaust system`s point of discharge the hydrogen concentration level shall not exceed 4 % average by volume during any moving three-second time interval during normal operation including start-up and shut down [1]. FC stack need to washout by the concentrated hydrogen as the purge gas and how to exhaust gas without exceeding 4 % is the most concerns. Also how to measure hydrogen pulse of millisecond in exhaust is also the rising up issue. In this paper model of FCV hydrogen discharge system was composed and variety of simple experiments were carried out to control the H2 concentration and release. In the case which the semiconductor sensor with porous material (average size less than quench distance) were applied to check H2 concentration the short pulse of high concentration of H2 in millisecond was hard to find. In this experiment the simple exhaust gas model H2/N2 flow was used instead of Air/H2. In the exhaust gas test experiment was conducted under the atmospheric condition in room temperature with small pressure difference and the fast solenoid valve to create quick hydrogen control. Most of the experiments except the turbulent flow experiments laminar flow is expected to be dominated when steady state condition is satisfied but the most result discussed here is the measurement of H2 concentration during the start point at the time of discharge within seconds. The results showed when H2 was added to N2 flow the boundary layer between N2 and H2 contained the high concentration of H2 at the initial wave front and decrease to reach steady state. This H2 pulse is typical in the FCV exhaust gas and topics of this paper.

A reflected shock wave in two-dimensional shock tube is studied numerically using Navier-Stokes equations with the detailed oxy-hydrogen reaction mechanism. The results show detailed process of mild ignition. The interaction between the reflected shock wave and the boundary layer yielded behind the incident shock wave produces clockwise and counter-clockwise vortices. These vortices generate compression waves. The future study related wall conditions (adiabatic or isothermal) will be shown at the conference site.

A two-dimensional (2-D) simulation of spontaneous ignition of high-pressure hydrogen in a length of duct is conducted in order to explore its underlying ignition mechanisms. The present study adopts a 2-D rectangular duct (i.e. not axisymmetric geometry) and focuses on the effects of initial diaphragm shape on the spontaneous ignitions. The Navier-Stokes equations with a detailed chemical kinetics mechanism are solved in a manner of direct numerical simulation. The detailed mechanisms of spontaneous ignition are discussed for each initial diaphragm shape. For a straight diaphragm shape it is found that the ignition occurs only near the wall due to the adiabatic wall condition while the three ignition events: ignitions due to leading shock wave reflection at the wall hydrogen penetration into shock-heated air near the wall and deep penetration of hydrogen into shock-heated air behind the leading shock wave are identified for a largely deformed diaphragm shape.

Stationary pressure vessels for the storage of large volumes of gaseous hydrogen at high pressure (>70 MPa) are typically manufactured from Cr-Mo steels. These steels display hydrogen-enhanced fatigue crack growth but pressure vessels can be manufactured using defect-tolerant design methodologies. However storage volumes are limited by the wall thickness that can be reliably manufactured for quench and tempered Cr-Mo steels typically not more than 25-35 mm. High-hardenability steels can be manufactured with thicker walls which enables larger diameter pressure vessels and larger storage volumes. The goal of this study is to assess the fracture and fatigue response of high hardenability Ni-Cr-Mo pressure vessel steels for use in high-pressure hydrogen service at pressure in excess of 1000 bar. Standardized fatigue crack growth tests were performed in gaseous hydrogen at frequency of 1Hz and for R-ratios in the range of 0.1 to 0.7. Elastic-plastic fracture toughness measurements were also performed. The measured fatigue and fracture behavior is placed into the context of previous studies on fatigue and fracture of Cr-Mo steels for gaseous hydrogen.

R&D projects for establishing hydrogen supply chain have already been started in Japan in collaboration among the industry government and universities. One of the important subjects of the project is development of liquefied hydrogen tankers i.e. ships carrying liquefied hydrogen in bulk. In general basic safety requirements should be determined to design ships. However the existing regulations do not specify the requirements for hydrogen tankers while requirements for ships carrying many kinds of liquefied gases are specified in “International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk” (IGC Code) issued by the International Maritime Organization i.e. a special organization under the United Nations. Therefore the basic safety requirements for hydrogen tankers should be developed. We conducted bibliographic survey on the IGC Code ISO/TR 15916:2004 “Basic considerations for the safety of hydrogen systems” and so on; in order to provide safety requirements taking into account the properties of liquid and gaseous hydrogen. In this paper we provide safety requirements for liquefied hydrogen tankers as the basis for further consideration by relevant governments.

Renewable energy is free abundant clean and could contribute towards a significant reduction of the global warming emissions. It is massively introduced as a source of electricity production across the globe and is expected to become the primary source of energy within the following decades. However despite the naturally replenished energy the supply is not always available. For this reason it is necessary at times of excess energy any surplus quantity to be sufficiently captured stored and later used when a deficit occurs. In this paper an overview of a backup power system operating with a hydrogen-biodiesel dual-fuel internal combustion engine is provided. The system is utilizing the organic chemical hydride method for safe hydrogen storage and transportation. The high energy content of hydrogen stored in the form of an organic hydride under ambient conditions makes it an ideal energy backup medium for large-scale and long-term applications. The research work focusses on the operation and emissions output of the dual-fuel internal combustion engine running on fully renewable fuels and the results are compared with the conventional petroleum-derived diesel engine. Biodiesel-hydrogen operation shows significant benefits in the reduction of carbon and soot emissions but deteriorates the NOx formation compared to the conventional diesel-powered engines. The operation of the engine at high loads can provide high exhaust thermal energy while alternative combustion strategies are necessary to be implemented at low load conditions for the optimum operation of the backup power system.

Fuel cell vehicles and some compressed natural gas vehicles are equipped with carbon fiber reinforced plastic (CFRP) composite cylinders. Each of the cylinders has a pressure relief device designed to detect heat and release the internal gas to prevent the cylinder from bursting in a vehicle fire accident. Yet in some accident situations the fire may be extinguished before the pressure relief device is activated leaving the high-pressure fuel gas inside the fire-damaged cylinder. To handle such a cylinder safely after an accident it is necessary that the cylinder keeps a sufficient post-fire strength against its internal gas pressure but in most cases it is difficult to accurately determine cylinder strength at the accident site. One way of solving this problem is to predetermine the post-fire burst strengths of cylinders by experiments. In this study automotive CFRP cylinders having no pressure relief device were exposed to a fire to the verge of bursting; then after the fire was extinguished the residual burst strengths and the overall physical state of the test cylinders were examined. The results indicated that the test cylinders all recorded a residual burst strength at least twice greater than their internal gas pressure for tested cylinders with new cylinder burst to nominal working pressure in the range 2.67–4.92 above the regulated ratio of 2.25.

A public survey was conducted in March 2015 in Japan asking public awareness knowledge perception and acceptance regarding hydrogen hydrogen infrastructure and fuel cell vehicle adopting the same key questions contained in the public surveys conducted six and seven years ago. Changes in answers between two different times of survey implementation were analyzed by comparing results of current survey to those of the previous surveys. Regression analyses were conducted and revealed influence of respondents’ awareness knowledge and perception about hydrogen hydrogen infrastructure and fuel cell vehicle on their acceptance on hydrogen station. We found a large increase in the awareness and relatively a small improvement on knowledge on hydrogen energy hydrogen infrastructure and fuel cell vehicle from the previous surveys. In contrast we did not find much changes in perception of risk and benefit perception on hydrogen society and hydrogen station and public acceptance of hydrogen infrastructure. Through the regression analyses we found large influences of negative risk perception of hydrogen itself and technology of hydrogen station and perception of necessity of hydrogen station on public acceptance of hydrogen station and the small influence of time background on the acceptance. Through the results of analyses implications to public communication in building public infrastructure are presented.

We conducted a fuelling test with hydrogen gas for a safety evaluation of the nozzle/receptacle at a controlled temperature and humidity. Test results confirmed that the nozzle/receptacle froze under specific conditions. However freezing did not cause apparatus damage nor hydrogen leakage. The nozzle/receptacle is thus able to fuel safely even if the nozzle/receptacle is stuck due to ice. In addition we quantified the water volume that causes freezing.

In the accident of Fukushima Daiichi nuclear power plants hydrogen was accumulated in the reactor buildings and exploded. To prevent such explosions hydrogen venting from reactor buildings is considered. When the gas mixture is released to a reactor building through a reactor containment together with the hydrogen some amount of steam might also be released. The steam condenses if the building atmosphere is below the saturation temperature and it affects the hydrogen behaviour. In this study the condensation effect to the hydrogen venting is evaluated using CFD analyses by comparing the case where a hydrogen-nitrogen mixture is released and the case where a hydrogen-steam mixture is released.

Propagation characteristics of hydrogen-air deflagration need to be understood for an accurate risk assessment. Especially flame propagation velocity is one of the most important factors. Propagation velocity of outwardly propagating flame has been estimated from burning velocity of a flat flame considering influence of thermal expansion at a flame front; however this conventional method is not enough to estimate an actual propagation velocity because flame propagation is accelerated owing to cellular flame front caused by intrinsic instability in hydrogen-air deflagration. Therefore it is important to understand the dynamic propagation characteristics of hydrogen-air deflagration. We performed explosion tests in a closed chamber which has 300 mm diameter windows and observed flame propagation phenomena by using Schlieren photography. In the explosion experiments hydrogen-air mixtures were ignited at atmospheric pressure and room temperature and in the range of equivalence ratio from 0.2 to 1.0. Analyzing the obtained Schlieren images flame radius and flame propagation velocity were measured. As the result cellular flame fronts formed and flame propagations of hydrogen–air mixture were accelerated at the all equivalence ratios. In the case of equivalent ratio φ = 0.2 a flame floated up and could not propagate downward because the influence of buoyancy exceeded a laminar burning velocity. Based upon these propagation characteristics a favorable estimation method of flame propagation velocity including influence of flame acceleration was proposed. Moreover the influence of intrinsic instability on propagation characteristics was elucidated.

To develop ultra high-strength cold stamping steels for automobile frame parts the effects of alloying elements on hydrogen embrittlement properties of ultra high-strength low alloy transformation induced plasticity (TRIP)-aided steels with a martensite matrix (TM steels) were investigated using the four-point bending test and conventional strain rate tensile test (CSRT). Hydrogen embrittlement properties of the TM steels were improved by the alloying addition. Particularly 1.0 mass% chromium added TM steel indicated excellent hydrogen embrittlement resistance. This effect was attributed to (1) the decrease in the diffusible hydrogen concentration at the uniform and fine prior austenite grain and packet block and lath boundaries; (2) the suppression of hydrogen trapping at martensite matrix/cementite interfaces owing to the suppression of precipitation of cementite at the coarse martensite lath matrix; and (3) the suppression of the hydrogen diffusion to the crack initiation sites owing to the high stability of retained austenite because of the existence of retained austenite in a large amount of the martensite–austenite constituent (M–A) phase in the TM steels containing 1.0 mass% chromium

For massive utilization of hydrogen energy it is necessary to transport a large quantity of hydrogen by liquefied hydrogen carriers. However the current rule on ships carrying liquefied hydrogen in bulks do not address the maritime transport of liquefied hydrogen and the safety assessment of liquefied hydrogen carriage is thus very important. In the present study we spilled liquefied hydrogen and LNG (Liquefied Natural Gas) on the surface of various materials and compared the difference of their spread and dispersion. Liquefied hydrogen immediately dispersed upward compared to LNG. Furthermore we also measured the flammability limit of low temperature hydrogen gas. Its range at low temperature was narrower than the range at normal temperature.

Wide use of hydrogen faces significant studies to resolve hydrogen safety issues in industries worldwide. However widely acceptable safety level standards are not achieved in the present situation yet. The present paper deals with hydrogen leaks from a tube to ignite and explode in atmosphere. The experiments using a shock tube are performed to clarify the auto-ignition property of high pressure hydrogen jet spouting from a tube. In order to improve experimental repeatability and reliability the shock tube with a plunger system is applied where the PET diaphragm is ruptured by a needle in order to control a diaphragm burst pressure (hydrogen pressure). As a result it becomes possible to control the diaphragm burst pressure to obtain a local minimum value. The most important result obtained in the preset study is that the minimum diaphragm burst pressure for auto-ignition is found between 1.0 and 1.2 m of tube length using a longer tube than the one used in the previous study. This minimum tube size is not found elsewhere to suggest that the tube length has a limit size for auto-ignition. Furthermore auto-ignition and Mach disk at the tube exit are observed using a high speed camera which is set at the frame speed of 1x105 fps when the ignited hydrogen jet is spouted out the tube.

Fuel-cell vehicle run on hydrogen is known that it has better energy efficiency than existing gasoline cars. The vehicles are designed so that hydrogen leaks from the tank are stopped automatically upon detection of hydrogen leakage or detection of impact in a collision. However we investigated the characteristics of hydrogen leakage sound from a hydrogen-leaking vehicle and the threshold of discrimination of hydrogen leakage from noise at a crossing with much traffic to examine a method to rescue people safely depending on the sense of hearing in the event of a continuous hydrogen leak. Here in the discrimination threshold test we conducted the test by using helium which is alternative gas of hydrogen leakage sound. We clarified that hydrogen leakage sound from vehicles has directivity height dependence and distance dependence. Furthermore we confirmed the threshold flow rate for distinguishing hydrogen gas when hydrogen leakage is heard at a distance of 5–10 m from the center of the hydrogen leaking vehicle in a 74 dB traffic noise environment.

We at Kawasaki have proposed a “CO2 free H2 chain” using the abundant brown coal of Australia as a hydrogen source. We developed the basic design package and finished the Front End Engineering Design (FEED) in 2014. There are not only the hazards of the processing plant system but also the characteristic hazards of a hydrogen plant system. We considered and carried out Hazard Identification (HAZID) as the most appropriate approach for safety design in this stage. This paper describes the safety design and HAZID which we practiced for the CO2-Free Hydrogen Supply Chain FEED.

If Hydrogen is expected to be highly valuable some improvements should be conducted mainly regarding the storage safety. To prevent from high pressure hydrogen composite tanks bursting the comprehension of the thermo-mechanics phenomena in the case of fire should be improved. To understand the kinetic of strength loss the heat flux produced by fire of various intensities should be assessed. This is the objective of this real scale experimental campaign which will allow studying in future works the strength loss of composite high-pressure vessels in similar fire conditions to the ones determined in this study. Fire calibration tests were performed on metallic cylinder vessels. These tests with metallic cylinders are critical in the characterization of the thermal load of various fire sources (pool fire propane gas fire hydrogen gas fire) so as to evaluate differences related to different thermal load. Radiant panels were also used as thermal source for reference of pure radiation heat transfer. The retained thermal load might be representative of accidental situations in worst case scenarios and relevant for a standardized testing protocol. The tests performed show that hydrogen gas fires and heptane pool fire allow reaching the target in terms of absorbed energy regarding the results of risk analysis performed previously. Other considerations can be taken into account that will led to retain an hydrogen gas fire for further works. Firstly hydrogen gas fire is the more realistic scenario: Hydrogen is the combustible that we every time find near an hydrogen storage. Secondly as one of the objectives of the project is to make recommendations for standardization issues it's important to note that gas fires are not too complex to calibrate control and reproduce. Finally due to previous considerations Hydrogen gas fire will be retained for thermal load of composite cylinders in future works.

In order to determine appropriate value for threshold stress intensity factor for hydrogen-assisted cracking (KIH) constant-displacement and rising-load tests were conducted in high-pressure hydrogen gas for JIS-SCM435 low alloy steel (Cr-Mo steel) used as stationary storage buffer of a hydrogen refuelling station with 0.2% proof strength and ultimate tensile strength equal to 772 MPa and 948 MPa respectively. Thresholds for crack arrest under constant displacement and for crack initiation under rising load were identified. The crack arrest threshold under constant displacement was 44.3 MPa m1/2 to 44.5 MPa m1/2 when small-scale yielding and plane-strain criteria were satisfied and the crack initiation threshold under rising load was 33.1 MPa m1/2 to 41.1 MPa m1/2 in 115 MPa hydrogen gas. The crack arrest threshold was roughly equivalent to the crack initiation threshold although the crack initiation threshold showed slightly more conservative values. It was considered that both test methods could be suitable to determine appropriate value for KIH for this material.

Hydrogen as a future energy carrier is receiving a significant amount of attention in Japan. From the viewpoint of safety risk evaluation is required in order to increase the number of hydrogen refuelling stations (HRSs) implemented in Japan. Collecting data about accidents in the past will provide a hint to understand the trend in the possibility of accidents occurrence by identifying its operation time However in new technology; accident rate estimation can have a high degree of uncertainty due to absence of major accident direct data in the late operational period. The uncertainty in the estimation is proportional to the data unavailability which increases over long operation period due to decrease in number of stations. In this paper a suitable time correlation model is adopted in the estimation to reflect lack (due to the limited operation period of HRS) or abundance of accident data which is not well supported by conventional approaches. The model adopted in this paper shows that the uncertainty in the estimation increases when the operation time is long owing to the decreasing data.

Risk assessment of hazardous material transport by road is critical in considering the spatial features of the transport route. However previous studies that focused on hydrogen transport were unable to reflect the spatial features in their risk assessments. Hence this study aims to assess the risk of hydrogen transport by road considering the spatial features of the transport route based on a geographic information system (GIS). This risk assessment method is conducted through a case study in Yokohama which is an advanced city for hydrogen economy in Japan. In our assessment the risk determined by multiplying the frequency of accidents with the consequence was estimated by road segments that constitute the entire transport route. The effects of the road structure and traffic volumes were reflected in the estimation of the frequency and consequence for each road segment. All estimations of frequency consequence and risk were conducted on a GIS compiled with the information regarding the road network and population. In the case study in Yokohama the route for the transport of compressed hydrogen was virtually set from the near-term perspectives. Based on the case study results the risks of the target transport route were assessed at an acceptable level under the previous risk criteria. The results indicated that the risks fluctuated according to the road segments. This implies that the spatial features of the transport route significantly affect the corresponding risks. This finding corroborates the importance of considering spatial features in the risk assessment of hydrogen transport by road. Furthermore the discussion of this importance leads to the capability of introducing hydrogen energy careers with high transport efficiency and transport routing to avoid high risk road segments as risk countermeasures.

The International Maritime Organization under the United Nations has developed safety requirements for seaborne transportation of hydrogen fuel cell vehicles in consideration of a recent increase in such transportation. Japan has led the development of new regulations in the light of some research outcomes including numerical simulations on hydrogen dispersion in a cargo space of a vehicle carrier in case of accidental leakage of hydrogen from the vehicle. Numerical results indicate that the region of space occupied by flammable hydrogen/air mixture strongly depends on the direction of ventilation openings. These findings have contributed to the development of new international regulations.

The fourth Strategic Energy Plan adopted in April 2014 stated ""a road map toward realization of a “hydrogen society” will be formulated and a council which comprises representatives of industry academia and government and which is responsible for its implementation will steadily implement necessary measures while progress is checked". Then the Council for a Strategy for Hydrogen and Fuel Cells which was held in June in the same year as a conference of experts from industry academia and government compiled a Strategic Roadmap for Hydrogen and Fuel Cells (hereinafter referred to as ""the Roadmap"") presenting efforts to be undertaken by concerned parties from the public/private sector aimed at building a hydrogen-based society.<br/>The Roadmap was revised in March 2016 in response to the progress of the efforts to include the schedule and quantitative targets to make the fuel cells for household use (Ene-Farm) fuel cell vehicles (FCVs) and hydrogen stations self-reliant. In April 2017 the first Ministerial Council on Renewable Energy Hydrogen and Related Issues was held. The Council decided to establish--by the end of the year--a basic strategy that would allow the government to press on with the measures in an integrated manner to realize a hydrogen-based society for the first time in the world. The second Ministerial Council on Renewable Energy Hydrogen and Related Issues was then held in December of that year to establish the Basic Hydrogen Strategy. The Strategy was positioned as a policy through which the whole government would promote relevant measures and proposed that hydrogen be another new carbon-free energy option. By setting a target to be achieved by around 2030 the Strategy provides the general direction and vision that the public and private sectors should share with an eye on 2050.<br/>Furthermore the fifth Strategic Energy Plan was adopted in July 2018. In order for hydrogen to be available as another new energy option in addition to renewable energy the Plan showed the correct direction of hydrogen energy in the energy policy specifically reducing the hydrogen procurement/supply cost to a level favorably comparable with that of existing energies while taking the calculated environmental value into account.

In the present study the self-ignition of high-pressure hydrogen released in atmospheric air through a diaphragm is visualized under various test conditions. The experimental results indicate that the hydrogen that jets through the rupturing diaphragm is mixed with the heated air near the tube wall. The self-ignition event originated from this mixing. The self-ignition was strongly dependent on the strength of an incident shock wave generated at the diaphragm rupture. As a result a cylindrical flame that formed after the self-ignition shows a tendency to become longer as it propagates in the downstream direction. The head velocities of the hydrogen-air mixture and the cylindrical flame are consistent with that of a contact surface calculated from the measured shock speed. A modified self-ignition mechanism is proposed based on the experimental observations.

Proper management of hydrogen gas is very important for safety security of nuclear power plants. Hydrogen removal by water formation reaction on a catalyst is one of the candidates for creating hydrogen free system. We observed in situ and time-resolved structure change of palladium metal nanoparticle catalyst during the water formation reaction by using X-ray absorption spectroscopy technique. A poisoning effect by carbon monoxide on catalytic activity was also studied. We have found that the creation of oxidized surface layer on palladium metal nanoparticles plays an important role for the water formation reaction process.

The pressure of compressed hydrogen changes with temperature when mass and volume are constant. Therefore when a compressed-hydrogen tank is filled with a certain amount of hydrogen it is necessary to adjust the filling pressure according to the gas temperature. In this study we conducted hydraulic pressure-cycle tests to investigate the fatigue life of Type-3 compressed-hydrogen tanks when environmental temperature and filling pressure are changed. The results indicated that the fatigue life at low temperatures (−40 °C 28 MPa) and room temperature (15 °C 35 MPa) was almost equal. However the fatigue life at high temperatures (85 °C 44 MPa) was shorter than that under other conditions suggesting that stress changes caused by thermal stress affect the fatigue life of the Type-3 tank.