Germany

Clarification of questions of safety represents a decisive contribution to the successful introduction of vehicles fuelled by hydrogen. At the moment the safety of hydrogen is being discussed and investigated by various bodies. The primary focus is on fuel-cell vehicles with hydrogen stored in gaseous form. This paper looks at the safety of hydrogen-fuelled vehicles with an internal combustion engine and liquefied hydrogen storage. The safety concept of BMW’s hydrogen vehicles is described and the specific aspects of the propulsion and storage concepts discussed. The main discussion emphasis is on the utilization of boil-off parking of the vehicles in an enclosed space and their crash behaviour. Theoretical safety observations are complemented by the latest experimental and test results. Finally reference is made to the topic-areas in the field of hydrogen safety in which cooperative research work could make a valuable contribution to the future of the hydrogen-powered vehicle.

An essential problem for the operation of high pressure water electrolyzers and fuel cells is the permissible contamination of hydrogen and oxygen. This contamination can create malfunction and in the worst case explosions in the apparatus and gas cylinders. In order to avoid dangerous conditions the exact knowledge of the explosion characteristics of hydrogen/air and hydrogen/oxygen mixtures is necessary. The common databases e.g. the CHEMSAFE® database published by DECHEMA BAM and PTB contains even a large number of evaluated safety related properties among other things explosion limits which however are mainly measured according to standard procedures under atmospheric conditions.<br/>Within the framework of the European research project “SAFEKINEX” and other research projects the explosion limits explosion pressures and rates of pressure rise (KG values) of H2/air and H2/O2 mixtures were measured at elevated conditions of initial pressures and temperatures by the Federal Institute of Materials Research and Testing (BAM). Empirical equations of the temperature influence could be deduced from the experimental values. An anomaly was found at the pressure influence on the upper explosion limits of H2/O2 and H2/air mixtures in the range of 20 bars. In addition explosion pressures and also rates of pressure rises have been measured for different hydrogen concentrations inside the explosion range. Such data are important for constructive explosion protection measures. Furthermore the mainly used standards for the determination of explosion limits have been compared. Therefore it was interesting to have a look at the systematic differences between the new EN 1839 tube and bomb method ASTM E 681-01 and German DIN 51649-1.

This paper presents a compilation of the results supplied by HySafe partners participating in the Standard Benchmark Exercise Problem (SBEP) V2 which is based on an experiment on hydrogen combustion that is first described. A list of the results requested from participants is also included. The main characteristics of the models used for the calculations are compared in a very succinct way by using tables. The comparison between results together with the experimental data when available is made through a series of graphs. The results show quite good agreement with the experimental data. The calculations have demonstrated to be sensitive to computational domain size and far field boundary condition.

This report commissioned by the Hydrogen Council and announced in conjunction with the launch of the initiative at the World Economic Forum in January 2017 details the future potential that hydrogen is ready to provide and sets out the vision of the Council and the key actions it considers fundamental for policy makers to implement to fully unlock and empower the contribution of hydrogen to the energy transition.

In this paper we explore the role of hydrogen in the energy transition including its potential recent achievements and challenges to its deployment. We also offer recommendations to ensure that the proper conditions are developed to accelerate the deployment of hydrogen technologies with the support of policymakers the private sector and society.

You can download the full report from the Hydrogen Council website here

Deployed at scale hydrogen could account for almost one-fifth of total final energy consumed by 2050. This would reduce annual CO2 emissions by roughly 6 gigatons compared to today’s levels and contribute roughly 20% of the abatement required to limit global warming to two degrees Celsius.

On the demand side the Hydrogen Council sees the potential for hydrogen to power about 10 to 15 million cars and 500000 trucks by 2030 with many uses in other sectors as well such as industry processes and feedstocks building heating and power power generation and storage. Overall the study predicts that the annual demand for hydrogen could increase tenfold by 2050 to almost 80 EJ in 2050 meeting 18% of total final energy demand in the 2050 two-degree scenario. At a time when global populations are expected to grow by two billion people by 2050 hydrogen technologies have the potential to create opportunities for sustainable economic growth.

“The world in the 21st century must transition to widespread low carbon energy use” said Takeshi Uchiyamada Chairman of Toyota Motor Corporation and co-chair of the Hydrogen Council. “Hydrogen is an indispensable resource to achieve this transition because it can be used to store and transport wind solar and other renewable electricity to power transportation and many other things. The Hydrogen Council has identified seven roles for hydrogen which is why we are encouraging governments and investors to give it a prominent role in their energy plans. The sooner we get the hydrogen economy going the better and we are all committed to making this a reality.”

Achieving such scale would require substantial investments; approximately US$20 to 25 billion annually for a total of about US$280 billion until 2030. Within the right regulatory framework – including long-term stable coordination and incentive policies – the report considers that attracting these investments to scale the technology is feasible. The world already invests more than US$1.7 trillion in energy each year including US$650 billion in oil and gas US$300 billion in renewable electricity and more than US$300 billion in the automotive industry.

“This study confirms the place of hydrogen as a central pillar in the energy transition and encourages us in our support of its large-scale deployment. Hydrogen will be an unavoidable enabler for the energy transition in certain sectors and geographies. The sooner we make this happen the sooner we will be able to enjoy the needed benefits of Hydrogen at the service of our economies and our societies” said Benoît Potier Chairman and CEO Air Liquide. “Solutions are technologically mature and industry players are committed. We need concerted stakeholder efforts to make this happen; leading this effort is the role of the Hydrogen Council.”

The launch of the new roadmap came during the Sustainability Innovation Forum in the presence of 18 senior members of the Hydrogen led by co-chairs Takeshi Uchiyamada Chairman of Toyota and Benoît Potier Chairman and CEO Air Liquide and accompanied by Prof. Aldo Belloni CEO of The Linde Group Woong-chul Yang Vice Chairman of Hyundai Motor Company and Anne Stevens Board Member of Anglo American. During the launch the Hydrogen Council called upon investors policymakers and businesses to join them in accelerating deployment of hydrogen solutions for the energy transition. It was also announced that Woong-chul Yang of Hyundai Motor Company will succeed Takeshi Uchiyamada of Toyota in the rotating role of the Council’s co-chair and preside the group together with Benoit Potier CEO Air Liquide in 2018. Mr Uchiyamada is planning to return as Co-chairman in 2020 coinciding with the Tokyo Olympic and Paalympic Games an important milestone for showcasing hydrogen society and mobility.

You can download the full report from the Hydrogen Council website here

Composite cylinders with metal liner are used for the storage of compressed hydrogen in automotive application. These hybrid pressure cylinders are designed for a nominal working pressure of up to 70 MPa. They also have to withstand a temperature range between -40°C and +85°C according GRPE draft [1] and for short periods up to a maximum temperature of 140°C during filling (fast filling) [2]. In order to exploit the material properties efficiently with a high degree of lightweight optimization and a high level of safety on the same time a better understanding of the structural behavior of hybrid designs is necessary. Work on this topic has been carried out in the frame of a work package on safety aspects and regulation (Subproject SAR) of the European IP StorHy (www.storhy.net). The temperature influence on the composite layers is distinctive due to there typical polymer material behavior. The stiffness of the composite layer is a function of temperature which influences global strains and stress levels (residual stresses) in operation. In order to do an accurate fatigue assessment of composite hybrid cylinders a realistic modeling of a representative temperature load is needed. For this climate data has been evaluated which were collected in Europe over a period of 30 years [3]. Assuming that the temperature follows a Gaussian (normal) distribution within the assessed period of 30 years it is possible to generate a frequency distribution for different temperature classes for the cold extreme and the hot extreme. Combining these distributions leads to the overall temperature range distribution (frequency over temperature classes). The climatic temperature influence the filling temperature and the pressure load have to be considered in combination with the operation profile of the storage cylinder to derive a complete load vector for an accurate assessment of the lifetime and safety level.

The use of hydrogen as an energy carrier is going to widen exponentially in the next years. In order to ensure the public acceptance of the new fuel not only the environmental impact has to be excellent but also the risk management of its handling and storage must be improved. As a part of modern risk assessment procedure CFD modeling of the accident scenario development must provide reliable data on the possible pressure loads resulted from explosion processes. The expected combustion regimes can be ranged from slow flames to deflagration-to-detonation transition and even to detonation. In the last case the importance of the reliability of simulation results is particularly high since detonation is usually considered as a worst case state of affairs. A set of large-scale detonation experiments performed in Kurchatov Institute at RUT facility was selected as benchmark. RUT has typical industry-relevant characteristic dimensions. The CFD codes possibilities to correctly describe detonation in mixtures with different initial and boundary conditions were surveyed. For the modeling two detonation tests HYD05 and HYD09 were chosen; both tests were carried out in uniform hydrogen/air mixtures; first one with concentration of 20.0% vol. and the second one with 25.5% vol. In the present exercise three CFD codes using a number of different models were used to simulate these experiments. A thorough inter-comparison between the CFD results including codes models and obtained pressure predictions was carried out and reported. The results of this inter comparison should provide a solid basis for the further code development and detonation models’ validation thus improving CFD predictive capabilities.

In many areas European research has been largely fragmented. To support the required integration and to focus and coordinate related research efforts the European Commission created a new instrument the Networks of Excellences (NoEs). The goal of the NoE HySafe has been to provide the basis to facilitate the safe introduction of hydrogen as an energy carrier by removing the safety related obstacles. The prioritisation of the HySafe internal project activities was based on a phenomena identification and ranking exercise (PIRT) and expert interviews. The identified research headlines were “Releases in (partially) confined areas” “Mitigation” and “Quantitative Risk Assessment”. Along these headlines existing or planned research work was re-orientated and slightly modified to build up three large internal research projects “InsHyde” “HyTunnel” and “HyQRA”. In InsHyde realistic indoor hydrogen leaks and associated hazards have been investigated to provide recommendations for the safe use of indoor hydrogen systems including mitigation and detection means. The appropriateness of available regulations codes and standards (RCS) has been assessed. Experimental and numerical work was conducted to benchmark simulation tools and to evaluate the related recommendations. HyTunnel contributed to the understanding of the nature of the hazards posed by hydrogen vehicles inside tunnels and its relative severity compared to other fuels. In HyQRA quantitative risk assessment strategies were applied to relevant scenarios in a hydrogen refuelling station and the performance was compared to derive also recommendations. The integration provided by the network is manifested by a series of workshops and benchmarks related to experimental and numerical work. Besides the network generated the following products: the International Conference on Hydrogen Safety the first academic education related to hydrogen safety and the Safety Handbook. Finally the network initiated the founding of the International Association for Hydrogen Safety which will open up the future networking to all interested parties on an international level. The indicated results of this five years integration activity will be described in short.

Solutions that simulate hydrometallurgical base metal process streams with high nickel (Ni) and minor platinum (Pt) concentrations were used to create Pt/Ni nanoparticles on TiO₂ nanotube surfaces. For this electrochemical deposition – redox replacement (EDRR) was used that also allowed to control the nanoparticle size density and Pt/Ni content of the deposited nanoparticles. The Pt/Ni nanoparticle decorated titanium dioxide nanotubes (TiO₂ nanotubes) become strongly activated for photocatalytic hydrogen (H₂) evolution. Moreover EDRR facilitates nanoparticle formation without the need for any additional chemicals and is more effective than electrodeposition alone. Actually a 10000-time enrichment level of Pt took place on the TiO₂ surface when compared to Pt content in the solution with the EDRR method. The results show that hydrometallurgical streams offer great potential as an alternative raw material source for industrial catalyst production when coupled with redox replacement electrochemistry.

We demonstrate that the combination of hydrogen release from a Liquid Organic Hydrogen Carrier (LOHC) system with electrochemical hydrogen compression (EHC) provides three decisive advantages over the state-of-the-art hydrogen provision from such storage system: a) The EHC device produces reduced hydrogen pressure on its suction side connected to the LOHC dehydrogenation unit thus shifting the thermodynamic equilibrium towards dehydrogenation and accelerating the hydrogen release; b) the EHC device compresses the hydrogen released from the carrier system thus producing high value compressed hydrogen; c) the EHC process is selective for proton transport and thus the process purifies hydrogen from impurities such as traces of methane. We demonstrate this combination for the production of compressed hydrogen (absolute pressure of 6 bar) from perhydro dibenzyltoluene at dehydrogenation temperatures down to 240 °C in a quality suitable for fuel cell operation e.g. in a fuel cell vehicle. The presented technology may be highly attractive for providing compressed hydrogen at future hydrogen filling stations that receive and store hydrogen in a LOHC-bound manner.

In this work new insights into impacts of the polytetrafluoroethylene (PTFE) binder on high temperature polymer electrolyte fuel cells (HT-PEFCs) are provided by means of various characterizations and accelerated stress tests. Cathodes with PTFE contents from 0 wt% to 60 wt% were fabricated and compared using electrochemical measurements. The results indicate that the cell with 10 wt% PTFE in the cathode catalyst layer (CCL) shows the best performance due to having the lowest mass transport resistance and cathode protonic resistance. Moreover cyclic voltammograms show that Pt (100) edge and corner sites are significantly covered by PTFE and phosphate anions when the PTFE content is higher than 25 wt%. Open-circuit and low load-cycling conditions are applied to accelerate degradation processes of the HT-PEFCs. The PTFE binder shows a network structure in the pores of the catalyst layer which reduces phosphoric acid leaching during the aging tests. In addition the high binder HT-PEFCs more easily suffer from a mass transport problem leading to more severe performance degradation.

A systematic method for obtaining a novel electrode structure based on PtCoMn ternary alloy catalyst supported on graphitic carbon nanofibers (CNF) for hydrogen evolution reaction (HER) in acidic media is proposed. Ternary alloy nanoparticles (Co0.6Mn0.4 Pt) with a mean crystallite diameter under 10 nm were electrodeposited onto a graphitic support material using a two-step pulsed deposition technique. Initially a surface functionalisation of the carbon nanofibers is performed with the aid of oxygen plasma. Subsequently a short galvanostatic pulse electrodeposition technique is applied. It has been demonstrated that if pulsing current is employed compositionally controlled PtCoMn catalysts can be achieved. Variations of metal concentration ratios in the electrolyte and main deposition parameters such as current density and pulse shape led to electrodes with relevant catalytic activity towards HER. The samples were further characterised using several physico-chemical methods to reveal their morphology structure chemical and electrochemical properties. X-ray diffraction confirms the PtCoMn alloy formation on the graphitic support and energy dispersive X-ray spectroscopy highlights the presence of the three metallic components from the alloy structure. The preliminary tests regarding the electrocatalytic activity of the developed electrodes display promising results compared to commercial Pt/C catalysts. The PtCoMn/CNF electrode exhibits a decrease in hydrogen evolution overpotential of about 250 mV at 40 mA cm⁻² in acidic solution (0.5 M H₂SO₄) when compared to similar platinum based electrodes (Pt/CNF) and a Tafel slope of around 120 mV dec−1 indicating that HER takes place under the Volmer-Heyrovsky mechanismm

Iron aluminides have been among the most studied intermetallics since the 1930s when their excellent oxidation resistance was first noticed. Their low cost of production low density high strength-to-weight ratios good wear resistance ease of fabrication and resistance to high temperature oxidation and sulfurization make them very attractive as a substitute for routine stainless steel in industrial applications. Furthermore iron aluminides allow for the conservation of less accessible and expensive elements such as nickel and molybdenum. These advantages have led to the consideration of many applications such as brake disks for windmills and trucks filtration systems in refineries and fossil power plants transfer rolls for hot-rolled steel strips and ethylene crackers and air deflectors for burning high-sulfur coal. A wide application for iron aluminides in industry strictly depends on the fundamental understanding of the influence of (i) alloy composition; (ii) microstructure; and (iii) number (type) of defects on the thermo-mechanical properties. Additionally environmental degradation of the alloys consisting of hydrogen embrittlement anodic or cathodic dissolution localized corrosion and oxidation resistance in different environments should be well known. Recently some progress in the development of new micro- and nano-mechanical testing methods in addition to the fabrication techniques of micro- and nano-scaled samples has enabled scientists to resolve more clearly the effects of alloying elements environmental items and crystal structure on the deformation behavior of alloys. In this paper we will review the extensive work which has been done during the last decades to address each of the points mentioned above.

The ultrafine-grained (UFG) duplex microstructure of medium-Mn steel consists of a considerable amount of austenite and ferrite/martensite achieving an extraordinary balance of mechanical properties and alloying cost. In the present work two heat treatment routes were performed on a cold-rolled medium-Mn steel Fe-12Mn-3Al-0.05C (wt.%) to achieve comparable mechanical properties with different microstructural morphologies. One heat treatment was merely austenite-reverted-transformation (ART) annealing and the other one was a successive combination of austenitization (AUS) and ART annealing. The distinct responses to hydrogen ingression were characterized and discussed. The UFG martensite colonies produced by the AUS + ART process were found to be detrimental to ductility regardless of the amount of hydrogen which is likely attributed to the reduced lattice bonding strength according to the H-enhanced decohesion (HEDE) mechanism. With an increase in the hydrogen amount the mixed microstructure (granular + lamellar) in the ART specimen revealed a clear embrittlement transition with the possible contribution of HEDE and H-enhanced localized plasticity (HELP) mechanisms.

The engineering correlations for assessment of hazard distance defined by a size of fireball after either liquid hydrogen spill combustion or high-pressure hydrogen tank rupture in a fire in the open atmosphere (both for stand-alone and under-vehicle tanks) are presented. The term “fireball size” is used for the maximum horizontal size of a fireball that is different from the term “fireball diameter” applied to spherical or semi-spherical shape fireballs. There are different reasons for a fireball to deviate from a spherical shape e.g. in case of tank rupture under a vehicle the non-instantaneous opening of tank walls etc. Two conservative correlations are built using theoretical analysis numerical simulations and experimental data available in the literature. The theoretical model for hydrogen fireball size assumes complete isobaric combustion of hydrogen in air and presumes its hemispherical shape as observed in the experiments and the simulations for tank rupturing at the ground level. The dependence of the fireball size on hydrogen mass and fireball’s diameter-to-height ratio is discussed. The correlation for liquid hydrogen release fireball is based on the experiments by Zabetakis (1964). The correlations can be applied as engineering tools to access hazard distances for scenarios of liquid or gaseous hydrogen storage tank rupture in a fire in the open atmosphere

The main goal of the project is to enable the wide adoption of H2NG (hydrogen in natural gas) blends by closing knowledge gaps regarding technical impacts on residential and commercial gas appliances. The project consortium will identify and recommend appropriate codes and standards that should be adapted to answer the needs and develop a strategy for addressing the challenges for new and existing appliances.<br/>This deliverable on market segmentation is part of work package 2 and provides a quantitative segmentation of the gas appliance market in terms of appliance population numbers. It therefore prepares the project partners to perform the subsequent selection of the most representative product types to be tested in the laboratories of the THyGA partners.<br/>The classification is developed to categorise appliances installed in the field based on available statistics calculation methods and estimations. As a result appliance populations are provided for each technology segment that draw a representative picture of the installed end-use appliances within the European Union in 2020.

As hydrogen-air mixtures are flammable in a wide range of concentrations and the minimum ignition energy is low compared to hydrocarbon fuels the safe handling of hydrogen is of utmost importance. Additional hazards may arise with the accidental spill of liquid hydrogen. Such a release of LH2 leads to a formation of a cryogenic pool a dynamic vaporization process and consequently a dispersion of gaseous hydrogen into the environment. Several LH2 release experiments as well as modelling approaches address this phenomenology. In contrast to existing approaches a new CFD model capable of simulating liquid and gaseous distribution was developed at Forschungszentrum Jülich. It is validated against existing experiments and yields no substantial lacks in the physical model and reveals a qualitatively consistent prediction. Nevertheless the deviation between experiment and simulation raises questions on the completeness of the database in particular with regard to the boundary conditions and available measurements.

High-pressure GH2 systems are of interest for storage and distribution of hydrogen. The dynamic blow-down process of a high-pressure GH2 reservoir in case of a small leak is a complex process involving a chain of distinct flow regimes and gas states which needs to be understood for safety investigations.<br/>This paper presents models to predict the hydrogen concentration and velocity field in the vicinity of a postulated small leak. An isentropic expansion model with a real gas equation of state for normal hydrogen is used to calculate the time dependent gas state in the reservoir and at the leak position. The subsequent gas expansion to 0.1 MPa is predicted with a zero-dimensional model. The gas conditions after expansion serve as input to a newly developed integral model for a round free turbulent H2-jet into ambient air. The model chain was evaluated by jet experiments with sonic hydrogen releases from different reservoir pressures and temperatures.<br/>Predictions are made for the blow-down of hydrogen reservoirs with 10 30 and 100 MPa initial pressure. The evolution of the pressure in the reservoir and of the H2 mass flux at the orifice are presented in dimensionless form which allows scaling to other system dimensions and initial gas conditions. Computed hydrogen concentrations and masses in the jet are given for the 100 MPa case. A normalized hydrogen concentration field in the free jet is presented which allows for a given leak scenario the prediction of the axial and radial range of burnable H2-air mixtures.

Hydrogen vehicles may emerge as a leading contender to replace today’s internal combustion engine powered vehicles. A Phenomena Identification and Ranking Table exercise conducted as part of the European Network of Excellence on Hydrogen Safety (HySafe) identified the use of hydrogen vehicles in road tunnels as a topic of important concern. An internal project called HyTunnel was duly established within HySafe to review identify and analyse the issues involved and to contribute to the wider activity to establish the true nature of the hazards posed by hydrogen vehicles in the confined space of a tunnel and their relative severity compared to those posed by vehicles powered by conventional fuels including compressed natural gas (CNG). In addition to reviewing current hydrogen vehicle designs tunnel design practice and previous research a programme of experiments and CFD modelling activities was performed for selected scenarios to examine the dispersion and explosion hazards potentially posed by hydrogen vehicles. Releases from compressed gaseous hydrogen (CGH2) and liquid hydrogen (LH2) powered vehicles have been studied under various tunnel geometries and ventilation regimes. The findings drawn from the limited work done so far indicate that under normal circumstances hydrogen powered vehicles do not pose a significantly higher risk than those powered by petrol diesel or CNG but this needs to be confirmed by further research. In particular obstructions at tunnel ceiling level have been identified as a potential hazard in respect to fast deflagration or even detonation in some circumstances which warrants further investigation. The shape of the tunnel tunnel ventilation and vehicle pressure relief device (PRD) operation are potentially important parameters in determining explosion risks and the appropriate mitigation measures.

Hydrogen energy is expanding world wide in recent years while hydrogen safety issues have drawn considerable attention. It is widely accepted that accidental hydrogen release in an open air environment will disperse quickly hence not causing significant hydrogen hazards. A hydrogen hazard is more likely to occur when hydrogen is accidentally released in a confined place i.e. parking garages and tunnels. Prediction the consequences of hydrogen detonation is important for hydrogen safety assessment and for ensuring the safety of installations during accidents. Hence an accident scenario of hydrogen release  nd detonation in a tunnel is analysed with GASFLOW-MPI in this paper. GASFLOW-MPI is a well validated parallel CFD code focusing on hydrogen transport combustion and detonation. GASFLOWMPI solves compressible Navier-Stokes equations with a powerful all-speed Arbitrary-Lagrangian-Eulerian (ALE) method hence it can cover both the non-compressible flow during the hydrogen relesase and dispersion phases and the compressible flow during combustion and detonation. A 3D model of a tunnel including eight cars is modelled. Firstly the hydrogen dispersion in the tunnel is calculated. Then the detonation in the tunnel is calculated by manually igniting the hydrogen at the top of the tunnel when the λ criterion is maximum. The pressure loads are calculated to evaluate the consequence of the hazard.

High-strength steels with yield strength of 960 MPa are susceptible to hydrogen-assisted cracking (HAC) during welding processing. In the present paper the implant test is used to study HAC in a quenched and tempered steel S960QL and a high-strength steel produced by thermo-mechanical controlled process S960MC. Welding is performed using the gas-metal arc welding process. Furthermore diffusible hydrogen concentration (H_D) in arc weld metal is determined. Based on the implant test results lower critical stress (LCS) for complete fracture critical implant stress (σ_krit) for crack initiation and embrittlement index (EI) are determined. At HD of 1.66 ml/100 g LCS is 605 MPa and 817 MPa for S960QL and S960MC respectively. EI is 0.30 and 0.46 for S960QL and S960MC respectively. Fracture surfaces of S960QL show higher degradation with reduced deformation. Both higher EI of S960MC and fractography show better resistance to HAC in the HAZ of S960MC compared to S960QL.

The recent growth of the net of hydrogen fuelling stations increases the demands to transport compressed hydrogen on road by battery vehicles or tube-trailers both in composite pressure vessels. As a transport regulation the ADR is applicable in Europe and adjoined regions and is used for national transport in the EU. This regulation provides requirements based on the behaviour of each individual pressure vessel regardless of the pressure of the transported hydrogen and relevant consequences resulting from generally possible worst case scenarios such as sudden rupture. In 2012 the BAM (German Federal Institute for Materials Research and Testing) introduced consequence-dependent requirements and established them in national transport requirements concerning the “UN service life checks” etc. to consider the transported volume and pressure of gases. This results in a requirement that becomes more restrictive as the product of pressure and volume increases. In the studies presented here the safety measures for hydrogen road transport are identified and reviewed through a number of safety measures from countries including Japan the USA and China. Subsequently the failure consequences of using trailer vehicles the related risk and the chance are evaluated. A benefit-related risk criterion is suggested to add to regulations and to be defined as a safety goal in standards for hydrogen transport vehicles and for mounted pressure vessels. Finally an idea is given for generating probabilistic safety data and for highly efficient evaluation without a significant increase of effort.

Liquid hydrogen (LH2) compared to compressed gaseous hydrogen offers advantages for large scale transport and storage of hydrogen with higher densities and potentially better safety performance. Although the gas industry has good experience with LH2 only little experience is available for the new applications of LH2 as an energy carrier. Therefore the European FCH JU funded project PRESLHY conducts pre-normative research for the safe use of cryogenic LH2 in non-industrial settings. The work program consists of a preparatory phase where the state of the art before the project has been summarized and where the experimental planning was adjusted to the outcome of a research priorities workshop. The central part of the project consists of 3 phenomena oriented work packages addressing Release Ignition and Combustion with analytical approaches experiments and simulations. The results shall improve the general understanding of the behavior of LH2 in accidents and thereby enhance the state-of-the-art what will be reflected in appropriate recommendations for development or revision of specific international standards. The paper presents the status of the project at the middle of its terms.

A series of experiments on hydrogen flame propagation in a thin layer geometry is presented. Premixed hydrogen-air compositions in the range from 6 to 15%(vol.) H2 are tested. Semi-open vertical combustion chamber consists of two transparent Plexiglas side walls with main dimensions of 90x20 cm with a gap from 1 to 10 mm in between. Test mixtures are ignited at the open end of the chamber so that the flame propagates towards the closed end. Ignition position changes from top to bottom in order to take into account an effect of gravity on flame propagation regimes. High-speed shadow imaging is used to visualize and record the combustion process. Thermal-diffusion and Darrieus-Landau instabilities are governing the general flame behaviour. Heat losses to side walls and viscous friction in a thin layer may fully suppress the flame propagation with local or global extinction. The sensitivity to heat losses can be characterized using a Peclet number as a ratio of layer thickness to laminar flame thickness. Approaching to critical Peclet number Pec = 42 the planar or wrinkled flame surface degradants to one-or two-heads "finger" flame propagating straight (for two-heads flame) or chaotic (for one-head "finger" flame). Such a "fingering" of the flame is found for the first time for gaseous systems and very similar to that reported for smouldering or filtering combustion of solid materials and also under micro-gravity conditions. The distance between "fingers" may depend on deficit of limiting component. The processes investigated can be very important from academic and practical points of view with respect to safety of hydrogen fuel cells.

This paper analyzes the behavior of residential solar-powered electrical energy storage systems. For this purpose a simulation model based on MATLAB/Simulink is developed. Investigating both short-time and seasonal hydrogen-based storage systems simulations on the basis of real weather data are processed on a timescale of 15 min for a consideration period of 3 years. A sensitivity analysis is conducted in order to identify the most important system parameters concerning the proportion of consumption and the degree of self-sufficiency. Therefore the influences of storage capacity and of storage efficiencies are discussed. A short-time storage system can increase the proportion of consumption by up to 35 percentage points compared to a self-consumption system without storage. However the seasonal storing system uses almost the entire energy produced by the photovoltaic (PV) system (nearly 100% self-consumption). Thereby the energy drawn from the grid can be reduced and a degree of self-sufficiency of about 90% is achieved. Based on these findings some scenarios to reach self-sufficiency are analyzed. The results show that full self-sufficiency will be possible with a seasonal hydrogen-based storage system if PV area and initial storage level are appropriate.

A hydrogen purification system based on the technology of the electrochemical hydrogen compression and purification is introduced. This system is developed within the scope of the project MEMPHYS. Therefore the project its targets and the different work stages are presented. The technology of the electrochemical purification and the state of the art of hydrogen purification are described. Early measurements in the project have been carried out and the results are shown and discussed. The ability of the technology to recover hydrogen from a gas mixture can be recognized and an outlook into further optimizations shows the future potential. A big advantage is the simultaneous compression of the purified hydrogen up to 200 bar therefore facilitating the transportation and storage.

In the present work a newly developed CFD deflagration model incorporated into the ADREA-HF code is evaluated against hydrogen vented deflagrations experiments carried out by KIT and FM-Global in a medium (1 m3) and a real (63.7 m3) scale enclosure respectively. A square vent of 0.5 m2 and 5.4 m2 respectively is located in the center of one of side walls. In the case of the medium scale enclosure the 18% v/v homogeneous hydrogen-air mixture and back-wall ignition case is examined. In the case of the real scale enclosure the examined cases cover different homogeneous mixture concentrations (15% and 18% v/v) different ignition locations (back-wall and center) and different levels of initial turbulence. The CFD model accounts for flame instabilities that develop as the flame propagates inside the chamber and turbulence that mainly develops outside the vent. Pressure predictions are compared against experimental measurements revealing a very good performance of the CFD model for the back-wall ignition cases. For the center ignition cases the model overestimates the maximum overpressure. The opening of the vent cover is identified as a possible reason for the overprediction. The analysis indicates that turbulence is the main factor which enhances external explosion strength causing the sudden pressure increase confirming previous findings.

Magnesium hydride owns the largest share of publications on solid materials for hydrogen storage. The “Magnesium group” of international experts contributing to IEA Task 32 “Hydrogen Based Energy Storage” recently published two review papers presenting the activities of the group focused on magnesium hydride based materials and on Mg based compounds for hydrogen and energy storage. This review article not only overviews the latest activities on both fundamental aspects of Mg-based hydrides and their applications but also presents a historic overview on the topic and outlines projected future developments. Particular attention is paid to the theoretical and experimental studies of Mg-H system at extreme pressures kinetics and thermodynamics of the systems based on MgH₂ nanostructuring new Mg-based compounds and novel composites and catalysis in the Mg based H storage systems. Finally thermal energy storage and upscaled H storage systems accommodating MgH₂ are presented.

The effect of hydrogen atoms at grain boundaries in metals is usually detrimental to the cohesion of the interface. This effect can be quantified in terms of the strengthening energy which is obtained following the thermodynamic model of Rice and Wang. A critical component of this model is the bonding or solution energy of the atoms to the free surfaces that are created during decohesion. At a grain boundary in a multicomponent system it is not immediately clear how the different species would partition and distribute on the cleaved free surfaces. In this work it is demonstrated that the choice of partitioning pattern has a significant effect on the predicted influence of H and C on grain boundary cohesion. To this end the Σ3(112)[11¯0] symmetric tilt grain boundary in bcc Fe with different contents of interstitial C and H was studied taking into account all possible distributions of the elements as well as surface diffusion effects. H as a single element has a negative influence on grain boundary cohesion independent of the details of the H distribution. C on the other hand can act both ways enhancing or reducing the cohesion of the interface. The effect of mixed H and C compositions depends on the partition pattern. However the general trend is that the number of detrimental cases increases with increasing H content. A decomposition of the strengthening energy into chemical and mechanical contributions shows that the elastic contribution dominates at high C contents while the chemical contribution sets the trend for high H contents.

Hydrogen embrittlement which severely affects structural materials such as steel comprises several mechanisms at the atomic level. One of them is hydrogen enhanced decohesion (HEDE) the phenomenon of H accumulation between cleavage planes where it reduces the interplanar cohesion. Grain boundaries are expected to play a significant role for HEDE since they act as trapping sites for hydrogen. To elucidate this mechanism we present the results of first-principles studies of the H effect on the cohesive strength of α-Fe single crystal (001) and (111) cleavage planes as well as on the Σ5(310)[001] and Σ3(112)[11¯0] symmetrical tilt grain boundaries. The calculated results show that within the studied range of concentrations the single crystal cleavage planes are much more sensitive to a change in H concentration than the grain boundaries. Since there are two main types of procedures to perform ab initio tensile tests different in whether or not to allow the relaxation of atomic positions which can affect the quantitative and qualitative results these methods are revisited to determine their effect on the predicted cohesive strength of segregated interfaces

An essential part of a safety analysis to evaluate the risks of a liquid hydrogen (LH2) containing system is the understanding of cryogenic pool spreading and its vaporization. It represents the initial step in an accident sequence with the inadvertent spillage of LH2 e.g. after failure of a transport container tank or the rupture of a pipeline. This stage of an accident scenario provides pertinent information as a source term for the subsequent analysis steps of atmospheric dispersion and at presence of an ignition source the combustion of the hydrogen-air vapor cloud. A computer model LAUV has been developed at the Research Center Juelich which is able to simulate the spreading and vaporization of a cryogenic liquid under various conditions such as different grounds (solid water). It is based on the so-called shallow-layer differential equations taking into account physical phenomena such as ice formation if the cryogen is spilled on a water surface. The presentation will give a description of the computer model and its validation against existing experimental data. Furthermore calculational results will be analyzed describing the prediction and quantification of the consequences of an LH2 spill for different cases. They also include the comparison of an LH2 spillage versus the corresponding release of other cryogens such as liquid natural gas liquid oxygen and liquid nitrogen.

The largest known experiment on hydrogen-air deflagration in the open atmosphere has been analysed by means of the large eddy simulation (LES). The combustion model is based on the progress variable equation to simulate a premixed flame front propagation and the gradient method to decouple the physical combustion rate from numerical peculiarities. The hydrodynamic instability has been partially resolved by LES and unresolved effects have been modelled by Yakhot's turbulent premixed combustion model. The main contributor to high flame propagation velocity is the additional turbulence generated by the flame front itself. It has been modelled based on the maximum flame wrinkling factor predicted by Karlovitz et al. theory and the transitional distance reported by Gostintsev with colleagues. Simulations are in a good agreement with experimental data on flame propagation dynamics flame shape and outgoing pressure wave peaks and structure. The model is built from the first principles and no adjustable parameters were applied to get agreement with the experiment.

The successful Computational Fluid Dynamics (CFD) benchmarking activity originally started within the EC-funded Network of Excellence HySafe (2004-2009) continues within the research topics of the recently established “International Association of Hydrogen Safety” (IA-HySafe). The present contribution reports the results of the standard benchmark problem SBEP-V21. Focus is given to hydrogen dispersion and accumulation within a non-ventilated ambient pressure garage both during the release and post-release periods but for very low release rates as compared to earlier work (SBEP-V3). The current experiments were performed by CEA at the GARAGE facility under highly controlled conditions. Helium was vertically released from the centre of the 5.76 m (length) x 2.96 m (width) x 2.42 m (height) facility 22 cm from the floor from a 29.7 mm diameter opening at a volumetric rate of 18 L/min (0.027 g/s equivalent hydrogen release rate compared to 1 g/s for SBEP-V3) and for a period of 3740 seconds. Helium concentrations were measured with 57 catharometric sensors at various locations for a period up to 1.1 days. The simulations were performed using a variety of CFD codes and turbulence models. The paper compares the results predicted by the participating partners and attempts to identify the reasons for any observed disagreements.

Liquid Organic Hydrogen Carrier (LOHC) systems offer a very attractive way for storing and distributing hydrogen from electrolysis using excess energies from solar or wind power plants. In this contribution an alternative high-value utilization of such hydrogen is proposed namely its use in steady-state chemical hydrogenation processes. We here demonstrate that the hydrogen-rich form of the LOHC system dibenzyltoluene/perhydro-dibenzyltoluene can be directly applied as sole source of hydrogen in the hydrogenation of toluene a model reaction for large-scale technical hydrogenations. Equilibrium experiments using perhydro-dibenzyltoluene and toluene in a ratio of 1:3 (thus in a stoichiometric ratio with respect to H2) yield conversions above 60% corresponding to an equilibrium constant significantly higher than 1 under the applied conditions (270 °C).

The work was done with respect to hydrogen safety of ITER vacuum vessel in cases of loss of cooling and loss of vacuum accidents. Experiments were conducted at sub-atmospheric pressures from 1 bar to 200 mbar and elevated temperatures up to 300 oC. Hydrogen concentration was changed from lower to upper flammability limits in all the range of pressures and temperatures. The experiments were performed in a spherical explosion bomb equipped with two quartz windows. The flame propagation velocity was measured using pressure method and high speed shadow cinematography. The theoretical flame velocities were calculated by Cantera code using Lutz and Mueller mechanisms. The influence of the initial temperature and pressure conditions on the laminar flame speed SL overall reaction order n and Markstein length LM are presented in this work and compared with the results of a theoretical model.

With regard to the goals of the European HySafe Network research facilities are essential for the experimental investigation of relevant phenomena for testing devices and safety concepts as well as for the generation of validation data for the various numerical codes and models. The integrating activity ‘Integration of Experimental Facilities (IEF)’ has provided basic support for jointly performed experimental work within HySafe. Even beyond the funding period of the NoE HySafe in the 6th Framework Programme IEF represents a long lasting effort for reaching sustainable integration of the experimental research capacities and expertise of the partners from different research fields. In order to achieve a high standard in the quality of experimental data provided by the partners emphasis was put on the know-how transfer between the partners. The strategy for reaching the objectives consisted of two parts. On the one hand a documentation of the experimental capacities has been prepared and analysed. On the other hand a communication base has been established by means of biannual workshops on experimental issues. A total of 8 well received workshops has been organised covering topics from measurement technologies to safety issues. Based on the information presented by the partners a working document on best practice including the joint experimental knowledge of all partners with regard to experiments and instrumentation was created. Preserving the character of a working document it was implemented in the IEF wiki website which was set up in order to provide a central communication platform. The paper gives an overview of the IEF network activities over the last 5 years.

An increase in use of hydrogen for energy storage and clean energy supply in a future energy and mobility market will strengthen the focus on safety and the safe handling of hydrogen facilities. The ability to simulate the whole chain of physical phenomena that may occur during an accident is mandatory for future safety studies on an industrial or urban scale. Together with the RWTH Aachen University Forschungszentrum Jülich (JÜLICH) develops numerical methods to predict safety incidents connected with the release of either LH2 or GH2 using the commercial CFD code ANSYS CFX. The full sequence from the release distribution or accumulation of accidentally released hydrogen till the mitigation of accident consequences by safety devices is considered. For specific phenomena like spreading and vaporization of LH2 pools or the operational behavior of passive auto-catalytic recombiners (PAR) in-house sub-models are developed and implemented. The paper describes the current development status gives examples of the validation and concludes with future work to provide the full range of hydrogen release and recombination simulation.

Gas sensors are applied for facilitating the safe use of hydrogen in for example fuel cell and hydrogen fuelled vehicles. New sensor developments aimed at meeting the increasingly stringent performance requirements in emerging applications are presented based on in-house technical developments and a literature study. The strategy of combining different detection principles i.e. sensors based on electrochemical cells semiconductors or field effects in combination with thermal conductivity sensor or catalytic combustion elements in one new measuring system is reported. This extends the dynamic measuring range of the sensor while improving sensor reliability to achieve higher safety integrity through diverse redundancy. The application of new nanoscaled materials nano wires carbon tubes and graphene as well as the improvements in electronic components of field-effect resistive-type and optical systems are evaluated in view of key operating parameters such as sensor response time low energy consumption and low working temperature.

There is a significant potential for nuclear combined heat and power (CHP) in quite a number of industries. The reactor concepts of the next generation would be capable to open up in particular the high temperature heat market where nuclear energy is applicable to the production processes of hydrogen (or liquid fuels) by steam reforming or water splitting. Due to the need to locate a nuclear facility near the hydrogen plant an overall safety concept has to deal with the question of safety of the combined nuclear/industrial system by taking into account a qualitatively new class of events characterized by interacting influences. Specific requirements will be determined by such factors as the reactor type the nature of the industrial process the separation distances of the industrial facility and population centers from the nuclear plant and prevailing public attitudes. Based on the Japanese concept of the GTHTR300C nuclear reactor for electricity and hydrogen cogeneration theoretical studies were conducted on the release dispersive transport and explosion of a hydrogen cloud in the atmosphere for the sake of assessing the required minimum separation distance to avoid any risk to the nuclear plant's safety systems. In the case of sulfur-iodine water splitting the accidental release of process intermediates including large amounts of sulfur dioxide sulfur trioxide and sulfuric acid need to be investigated as well to estimate the potential risk to nuclear installations like the operators' room and estimate appropriate separation distances against toxic gas propagation. Results of respective simulation studies will be presented.

Zero Emission Vehicles (ZEVs) are necessary to help reduce the emissions in the transportation sector which is responsible for 40% of overall greenhouse gas emissions. There are two types of ZEVs Battery Electric Vehicles (BEVs) and Fuel Cell Electric Vehicles (FCEVs) Commercial Success of BEVs has been challenging thus far also due to limited range and very long charging duration. FCEVs using H2 infrastructure with SAE J2601 and J2799 standards can be consistently fuelled in a safe manner fast and resulting in a range similar to conventional vehicles. Specifically fuelling with SAE J2601 with the SAE J2799 enables FCEVs to fill with hydrogen in 3-5 minutes and to achieve a high State of Charge (SOC) resulting in 300+ mile range without exceeding the safety storage limits. Standardized H2 therefore gives an advantage to the customer over electric charging. SAE created this H2 fuelling protocol based on modelling laboratory and field tests. These SAE standards enable the first generation of commercial FCEVs and H2 stations to achieve a customer acceptable fueling similar to today's experience. This report details the advantages of hydrogen and the validation of H2 fuelling for the SAE standards.

The BMW Hydrogen 7 is the world’s first premium sedan with a bi-fuelled internal combustion engine concept that has undergone the series development process. This car also displays the BMW typical driving pleasure. During development the features of the hydrogen energy source were emphasized. Engine tank system and vehicle electronics were especially developed as integral parts of the vehicle for use with hydrogen. The safety-oriented development process established additional strict hydrogen-specific standards for the Hydrogen 7. The fulfilment of these standards were demonstrated in a comprehensive experimentation and testing program which included all required tests and a large number of additional hydrogen-specific crash tests such as side impacts to the tank coupling system or rear impacts. Furthermore the behaviour of the hydrogen tank was tested under extreme conditions for instance in flames and after strong degradation of the insulation. Testing included over 1.7 million km of driving; and all tests were passed successfully proving the intrinsic safety of the vehicle and also confirming the success of the safety-oriented development process which is to be continued during future vehicle development. A safety concept for future hydrogen vehicles poses new challenges for vehicles and infrastructure. One goal is to develop a car fuelled by hydrogen only while simultaneously optimizing the safety concept. Another important goal is removal of (self-imposed) restrictions for parking in enclosed spaces such as garages. We present a vision of safety standards requirements and a program for fulfilling them.

Hydrogen is expected to become a key component in the decarbonized energy systems of the future. Its unique chemical characteristics make hydrogen a carbon-free fuel that is suitable to be used as broadly as fossil fuels are used today. Since hydrogen can be produced by splitting water molecules using electricity as the only energy input needed hydrogen offers the opportunity to produce a fully renewable fuel if the electricity input also only stems from renewable sources. Once renewable electricity is converted into hydrogen it can be stored over long periods of time and transported over long even intercontinental distances. Underground hydrogen storage pipelines compressors liquefaction-units and transportation ships are infrastructures and suitable technologies to establish a global hydrogen energy system. Several chemical synthesis routes exist to produce more complex products from green hydrogen to fulfil the demands of various end-users and industries. One exemplary power-to-gas product is methane which can be used as a natural gas substitute. Furthermore ammonia alcohols kerosene and all other important products from hydrocarbon chemistry can be synthesized using green hydrogen.

Structures formed during gas mixing following an injection of a gas into atmosphere are analyzed using optic methods based on the detection of density non-uniformities. Methods for determination of fractal parameters for a random distribution of these non-uniformities are described and information revealed on the gas mixing structure is analyzed. The BOS (background oriented schlieren) technique is utilized to obtain the optical image of the forming structures which afterward is processed using the correlation procedure allowing to extract the quantitative information on the mixing. Additionally a possibility to link the characteristics of the injected gas source and the system fractal parameters was demonstrated. The method can be used in the development of the non-contact methods for the evaluation of the gaseous system parameters based on the optical diagnostics and potentially for the obtaining more detailed information of the gaseous turbulence.

Shipping accounts for about 3% of global CO2 emissions. In order to achieve the target set by the Paris Agreement IMO introduced their GHG strategy. This strategy envisages 50% emission reduction from international shipping by 2050 compared with 2008. This target cannot be fulfilled if conventional fuels are used. Amongst others hydrogen is considered to be one of the strong candidates as a zero-emissions fuel. Yet concerns around the safety of its storage and usage have been formulated and need to be addressed. “Safety” in this article is defined as the control of recognized hazards to achieve an acceptable level of risk. This article aims to propose a new way of comparing two systems with regard to their safety. Since safety cannot be directly measured fuzzy set theory is used to compare linguistic terms such as “safer”. This method is proposed to be used during the alternative design approach. This approach is necessary for deviations from IMO rules for example when hydrogen should be used in shipping. Additionally the properties of hydrogen that can pose a hazard such as its wide flammability range are identified.

Hydrogen energy applications often require that systems are used indoors (e.g. industrial trucks for materials handling in a warehouse facility fuel cells located in a room or hydrogen stored and distributed from a gas cabinet). It may also be necessary or desirable to locate some hydrogen system components/equipment inside indoor or outdoor enclosures for security or safety reasons to isolate them from the end-user and the public or from weather conditions.<br/>Using of hydrogen in confined environments requires detailed assessments of hazards and associated risks including potential risk prevention and mitigation features. The release of hydrogen can potentially lead to the accumulation of hydrogen and the formation of a flammable hydrogen-air mixture or can result in jet-fires. Within Hyindoor European Project carried out for the EU Fuel Cells and Hydrogen Joint Undertaking safety design guidelines and engineering tools have been developed to prevent and mitigate hazardous consequences of hydrogen release in confined environments. Three main areas are considered: Hydrogen release conditions and accumulation vented deflagrations jet fires and including under-ventilated flame regimes (e.g. extinguishment or oscillating flames and steady burns). Potential RCS recommendations are also identified.

The flame velocities of unconfined gas explosions depend on the cloud size and the distance from the initiating source. The mechanisms for this effect are not fully understood; a possible explanation is turbulence generated by the propagating flame front. The molecular bands in the flame front are exposed to continuously increasing radiation intensity of water bands in the interior of the reaction product ball. A first approach to verifying this assumption is described in this paper. The flame propagation was observed by high speed video techniques including time resolved spectroscopy in the UV-Vis-NIR spectral range with a time resolution up to 3000 spectra/s. Ignition flame head velocity flame contours reacting species and temperatures were evaluated. The evaluation used video brightness subtraction and 1-dimensional image contraction to obtain traces of the movements perpendicular to the direction of propagation. Flame front velocities are found to be between 16m/s and 25 m/s. Analysis focused in particular on the flame front which is not smooth. Salients emerge on the surface to result in the well-known cellular structures. The radiation of various bands from the fire ball on the reacting species is estimated to have an influence on the flame velocity depending on the distance from initiation. Evaluation of OH-band and water band spectra might indicate might indicate higher temperatures of the flame front induced by radiation of the fireball. But it is difficult to verify the effect relative to competing flame acceleration mechanisms.

The possibility of flame acceleration (FA) and deflagration-to-detonation transition (DDT) when homogeneous hydrogen-carbon monoxide-air (H2-CO-air) mixtures are used rises the need for an efficient simulation approach for safety assessment. In this study a modelling approach for H2-CO-air flames incorporating deflagration and detonation within one framework is presented. It extends the previous work on H2-air mixtures. The deflagration is simulated by means of the turbulent flame speed closure model incorporating a quenching term. Since high flow velocities e.g. the characteristic speed of sound of the combustion products are reached during FA the flow passing obstacles generates turbulence at high enough levels to partially quench the flame. Partial flame quenching has the potential to stall the onset of detonation. An altered formulation for quenching is introduced to the modelling approach to better account for the combustion characteristics for accelerating lean H2-CO-air flames. The presented numerical approach is validated with experimental flame velocity data of the small-scale GraVent test rig [1] with homogeneous fuel contents of 22.5 and 25.0 vol-% and fuel compositions of 75/25 and 50/50 vol-% H2/CO respectively. The impact of the quenching term is further discussed on simulations of the FZK-7.2m test rig [2] whose obstacle spacing is smaller than the spacing in the GraVent test rig.

Gas systems can provide considerable flexibility in integrated energy systems to accommodate hydrogen produced from Power-to-Hydrogen units using excess volatile renewable energy generation. To use the flexibility in integrated energy systems while ensuring a secure and reliable system operation gas system operators need to accurately and easily analyze the effects of varying hydrogen levels on the dynamic gas behavior and vice versa. Existing methods for hydrogen tracking however either solve the hydrogen propagation and dynamic gas behavior separately or must cope with a large inaccuracy. Hence existing methods do not allow an accurate and coupled analysis of gas systems in integrated energy systems considering varying hydrogen levels. This paper proposes a calorific-value-gradient method which can accurately track the propagation of varying hydrogen levels in a gas system even with large simulation time increments of up to one hour. The new method is joined and simultaneously solved with an implicit finite difference scheme describing the transient gas behavior in a single equation system in a coupled Newton–Raphson gas flow calculation. As larger simulation time increments can be chosen without reducing the accuracy the computation time can be strongly reduced compared to existing Euler-based methods. With its high accuracy and its coupled approach this paper provides gas system operators a method to accurately analyze how the propagation of hydrogen affects the entire gas system. With its coupled approach the presented method can enhance the investigation of integrated energy systems as the transient gas behavior and varying hydrogen propagation of the gas system can be easily included in such analyses.

In order to simulate an accidental hydrogen release from the low pressure pipe system of a hydrogen vehicle a systematic study on the nature of transient hydrogen jets into air and their combustion behaviour was performed at the FZK hydrogen test site HYKA. Horizontal unsteady hydrogen jets with an amount of hydrogen up to 60 STP dm3 and initial pressures of 5 and 16 bar have been investigated. The hydrogen jets were ignited with different ignition times and positions. The experiments provide new experimental data on pressure loads and heat releases resulting from the deflagration of hydrogen-air clouds formed by unsteady turbulent hydrogen jets released into a free environment. It is shown that the maximum pressure loads occur for ignition in a narrow position and time window. The possible hazard potential arising from an ignited free transient hydrogen jet is described.

In order to simulate an accidental hydrogen release from the high pressure pipe system of a hydrogen facility a systematic study on the nature of transient hydrogen jets into air and their combustion behavior was performed at the KIT hydrogen test site HYKA. Horizontal unsteady hydrogen jets from a reservoir of 0.37 dm3 with initial pressures of up to 200 bar have been investigated. The hydrogen jets released via round nozzles 3 4 and 10 mm were ignited with different ignition times and positions. The experiments provide new experimental data on pressure loads and heat releases resulting from the deflagration of hydrogen–air clouds formed by unsteady turbulent hydrogen jets released into a free environment. It is shown that the maximum pressure loads occur for ignition in a narrow position and time window. The possible hazard potential arising from an ignited free transient hydrogen jet is described.