Publications

In any application involving the production storage or use of hydrogen sensors are important devices for alerting to the presence of leaked hydrogen. Hydrogen sensors should be accurate sensitive and specific as well as resistant to long term drift and varying environmental conditions. Furthermore as an integral element in a safety system sensor performance should not be compromised by operational parameters. For example safety sensors may be required to operate at reduced oxygen levels relative to air. In this work we evaluate and compare a number of sensor technologies in terms of their ability to detect hydrogen under conditions of varying oxygen concentration.

The paper presents results of experimental investigations of different phlegmatizator substances and its binary compounds used for full hydrogen combustion suppression. The work was performed in experimental facilities of three different scales (small medium and large) at normal initial pressure and temperature range 20 ⎯ 120 °С. Ten individual substances and six binary compounds were tested in a small scale experiments. Three individual halogen containing substances capable of full suppression of hydrogen combustion were found in a series of small scale experiments (tube length – 1 m ID – 66 mm). The minimum concentration of the most effective substance was 11% at 20°С and 14% at 120°С in a small scale experiments. Medium scale confined and large scale unconfined experiments confirmed the possibility of full combustion suppression. The minimum concentration of the most effective binary mixture was found to be 12 % at 20°С in a large scale experiments.

In this study the flame propagation behavior and the intensity of blast wave by an accidental explosion of a hydrogen/air mixture in an open space have been measured simultaneously by using soap bubble method. The results show that the flame in lean hydrogen/air mixtures propagated with a wrinkled flame by spontaneous instability. The flame in rich hydrogen/air mixtures propagated smoothly in the early stage and was intensively wrinkled and accelerated in the later stage by different type of instability. The intensity of the blast wave of hydrogen/air mixtures is strongly affected by the acceleration of the flame propagation by these spontaneous flame disturbances.

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.

This experimental work analyzes the hydrogen embrittlement mechanism in quenched and tempered low-alloyed steels. Experimental tests were performed to study hydrogen diffusion under applied cyclic loading. The permeation curves were fitted by considering literature models in order to evaluate the role of trapping—both reversible and irreversible—on the diffusion mechanism. Under loading conditions a marked shift to the right of the permeation curves was noticed mainly at values exceeding the tensile yield stress. In the presence of a relevant plastic strain the curve changes due to the presence of irreversible traps which efficiently subtract diffusible atomic hydrogen. A significant reduction in the apparent diffusion coefficient and a considerable increase in the number of traps were noticed as the maximum load exceeded the yield strength. Cyclic loading at a tensile stress slightly higher than the yield strength of the material increases the hydrogen entrapment phenomena. The tensile stress causes a marked and instant reduction in the concentration of mobile hydrogen within the metal lattice from 55% of the yield strength and it increases significantly in the plastic field.

Since the rapid development of hydrogen stationary and vehicle fuel cells the last decade it is of importance to improve the prediction of overpressure generated during an accidental explosion which could occur in a confined part of the system. To this end small-scale vented hydrogen–air explosions were performed in a transparent cubic enclosure with a volume of 3375 cm3. The flame propagation was followed with a high speed camera and the overpressure inside the enclosure was recorded using high frequency piezoelectric transmitters. The effects of vent area and ignition location on the amplitude of pressure peaks in the enclosed volume were investigated. Indeed vented deflagration generates several pressures peaks according to the configuration and each peak can be the dominating pressure. The parametric study concerned three ignition locations and five square vent sizes.

Computational fluid dynamics is used to simulate the release of high pressure Hydrogen from a reservoir with an exit of increasing diameter. Abel-Noble real gas equation of state is used to accurately simulate this high pressure release. Parallel processing based on Message Passing Interface for domain decomposition is employed to decrease the solution time. The release exit boundary is increased in time to simulate a scenario when the exit area increases during the release. All nodes and elements are moved accordingly at each time step to maintain the quality of the mesh. Different speeds of increasing diameter are investigated to see the impact on this unsteady flow.

A crucial problem of new hydrogen technologies is the lightweight and also safe storage of acceptable amounts of hydrogen for portable or mobile applications. A new and innovative technology based on capillary arrays has been developed. These systems ensure safe infusion storage and controlled release of hydrogen gas although storage pressures up to 1200 bar are applied. This technology enables the storage of a significantly greater amount of hydrogen than other approaches. In storage tests with first capillary arrays a gravimetric storage capacity of about 33% and a volumetric capacity of 28% was determined at a comparative low pressure of only 400 bar. This is much more than the actual published storage capacities which are to find for other storage systems. This result already surpassed the US Department of Energy's 2010 target and it is expected to meet the DOE's 2015 target in the near future.<br/>Different safety aspects have been evaluated. On the one hand experiments with single capillaries or arrays of them have been carried out. The capillaries are made of quartz and other glasses. Especially quartz has a three times higher strength than steel. At the same time the density is about three times lower which means that much less material is necessary to reach the same pressure resistance. The pressure resistance of single capillaries has been determined in dependence of capillary materials and dimensions wall thickness etc. in order to find out optimal parameters for the “final” capillaries. In these tests also the sudden release of hydrogen was tested in order to observe possible spontaneous ignitions. On the other hand a theoretical evaluation of explosion hazards was done. Different situations were analyzed e.g. release of hydrogen by diffusion or sudden rupture.

For the general public to use hydrogen as a vehicle fuel they must be able to handle hydrogen with the same degree of confidence as conventional liquid and gaseous fuels. The hazards associated with jet releases from accidental leaks in a vehicle-refuelling environment must be considered if hydrogen is stored and used as a high-pressure gas since a jet release can result in a fire or explosion. This paper describes the work done by us in modelling some of the consequences of accidental releases of hydrogen implemented in our Fire Explosion Release Dispersion (FRED) software. The new dispersion model is validated against experimental data available in the open literature. The model predictions of hydrogen gas concentration as a function of distance are in good agreement with experiments. In addition FRED has been used to model the consequence of the bursting of a vessel containing compressed hydrogen. The results obtained from FRED i.e. overpressure as a function of distance match well in comparison to experiments. Overall it is concluded that FRED can model the consequences of an accidental release of hydrogen and the blast waves generated from bursting of vessel containing compressed hydrogen

The International Energy Agency's Hydrogen Implementing Agreement (IEA HIA) was established in 1977 to pursue collaborative hydrogen research and development and information exchange among its member countries. Information and knowledge dissemination is a key aspect of the work within IEA HIA tasks and case studies technical reports and presentations/publications often result from the collaborative efforts. The work conducted in hydrogen safety under Task 31 and its predecessor Task 19 can positively impact the objectives of national programs even in cases for which a specific task report is not published. The interactions within Task 31 illustrate how technology information and knowledge exchange among participating hydrogen safety experts serve the objectives intended by the IEA HIA.

The California Fuel Cell Partnership (CaFCP) is currently working with key stakeholders like the US Department of Energy (DOE) and National Fire Protection Association (NFPA) to develop a national template for educating and training first responders about hydrogen fuel cell-powered vehicles (FCV) and hydrogen fuelling infrastructure. Currently there are several existing programs that either have some related FCV/hydrogen material or have plans to incorporate this in the future. To create a robust national emergency responder (ER) program the strongest elements from these existing programs are considered for incorporation into the template. Working with the key stakeholders the national template will be evaluated on a regular basis to ensure accurate and up to date information and resources and effective teaching techniques for the emergency response community. This paper describes the evaluation process discusses elements of the template and reports on the steps and progress to implementation; all in the effort to effectively support the emergency response community as hydrogen infrastructure develops and FCVs are leased or sold.

In future pressure relief devices (PRDs) should be installed on hydrogen vehicles to prevent a hydrogen container burst in the event of a nearby fire. Weakening of the container at elevated temperature could result in such burst. In this case the role of a PRD is to release some or all of the system fluid in the event of an abnormally high pressure. The paper analyzes the possibility of hydrogen self-ignition at PRD operation and ways of its prevention.

The dynamics of detonation transmission from a straight channel into a curved chamber was investigated as a function of initial pressure using a combined experimental and numerical study. Hi-speed Schlieren and *OH chemiluminescense were used for flow visualization; numerical simulations considered the two-dimensional reactive Euler equations with detailed chemistry. Results show the highly transient sequence of events (i.e. detonation diffraction re-initiation attempts and wave reflections) that precede the formation of a steadily rotating Mach detonation along the outer wall of the chamber. An increase in pressure from 15 kPa to 26 kPa expectedly resulted in detonations that are less sensitive to diffraction. Local quenching of the initial detonation occurred for all pressures considered. The location where this decoupling occurred along the inner wall determined the location where transition from regular reflection to a rather complex wave structure occurred along the outer wall. This complex wave structure includes a steadily rotating Mach detonation (stem) an incident decoupled shock-reaction zone region and a transverse detonation that propagates in pre-shocked mixture.

The acoustic to the parametric instability has been studied for H2-air mixtures at normal conditions. Two approaches for the investigation of the problem have been considered. The simplified analytical model proposed by Bychkov was selected initially. Its range of applicability resulted to be very restricted and therefore numerical solutions of the problem were taken into account. The results obtained were used to study the existence of spontaneous transition from the acoustic to the parametric instability for different fuel concentrations. Finally the growth rate of the instabilities was numerically calculated for a set of typical mixtures for hydrogen safety.

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 transition to a more sustainable personal transportation sector requires the widespread adoption of electric vehicles. However a dominant design has not yet emerged and a standards battle is being fought between battery and hydrogen fuel cell powered electric vehicles. The aim of this paper is to analyze which factors are most likely to influence the outcome of this battle thereby reducing the uncertainty in the industry regarding investment decisions in either of these technologies. We examine the relevant factors for standard dominance and apply a multi-criteria decision-making method best worst method to determine the relative importance of these factors. The results indicate that the key factors include technological superiority compatibility and brand reputation and credibility. Our findings show that battery powered electric vehicles have a greater chance of winning the standards battle. This study contributes to theory by providing further empirical evidence that the outcome of standards battles can be explained and predicted by applying factors for standard success. We conclude that technology dominance in the automotive industry is mostly driven by technological characteristics and characteristics of the format supporter.

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.

We present an experimental investigation of the different concentration build-up regimes encountered during a release of helium/air mixture in an empty enclosure without ventilation. The release is a vertical jet issuing from a nozzle located near the floor. The nozzle diameter the flow rate and the composition of the injected mixture have been varied such that the injection Richardson number ranges from 6 × 10−6 to 190. The volume Richardson number which gives the ability of the release to mix the enclosure content ranges from 2 × 10−3 to 2 × 104. This wide range allowed reaching three distinct regimes: stratified stratified with a homogeneous upper layer and homogenous.

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 this paper the detonation propensity of different compositions of mixtures of hydrogen propane and methane with air has been evaluated over a wide range of compositions. We supplement the conventional calculations of the induction delay with calculations of the characteristic acceleration parameter recently suggested by Radulescu Sharpeand Bradley(RSB) to characterize the instability of detonations. While it is well established that the ignition delay provides a good measure for detonability the RSB acceleration or its non-dimensionalform provides a further discriminant between mixtures with similar ignition delays. The present assessment of detonability reveals that while a stoichiometric mixture of hydrogen-air has an ignition delay one and two orders of magnitude shorter than respectively propane and methane hydrogen also has a parameter smaller by respectively one and two orders of magnitude. Its smaller propensity for instability is reflected by an RSB acceleration parameter similar to the two hydrocarbons. The predictions however indicate that lean hydrogen mixtures are likely to be much more unstable than stoichiometric ones. The relation between the parameter and potential to amplify an unstable transverse wave structure has been further determined through numerical simulation of decaying reactive Taylor-Sedov blast waves. Using a simplified two-step model calibrated for these fuels we show that methane mixtures develop cellular structures more readily than propane and hydrogen when observed on similar induction time scales. Future work should be devoted towards a quantitative inclusion of the RSB parameter in assessing the detonability of a given mixture.

Most studies on blast waves generated by gas explosions have focused on gas explosions occurring in open spaces. However accidental gas explosions often occur in confined spaces and the blast wave generates from a bursting vessel as a result of an increase in pressure caused by the gas explosion. In this study blast waves from bursting plastic vessels in which gas explosions occurred are investigated. The flammable mixtures used in the experiments were hydrogen-air mixtures at several equivalence ratios and a stoichiometric methane-air mixture. The overpressures of the blast waves were generated by venting high-pressure gas in the enclosure and volumetric expansion with a combustion reaction. The measured intensities of the blast waves were greater than the calculated values resulting from high-pressure bursting without a combustion reaction. The intensities of the blast waves resulting from the explosions of hydrogen-air mixtures were much greater than those of the methane-air mixture.

In this study the spread of cryogenic liquid due to a limited period of release is investigated for the first time to clarify the unclear conventional concept regarding two release types continuous and instantaneous release. In describing instantaneous release a discharge time has been assumed to be infinitesimally small; however such an assumption is unreal because there exists a finite period of release no matter how rapid it is. If the discharge time is less than the entire time domain the instantaneous release model should be added to the continuous model from the end of the time. This combined release that consists of the initial continuous model and subsequent instantaneous model is more realistic than the instantaneous release. The physical phenomenon is governed by three parameters: the evaporation rate per unit area release time and spill quantity. Third-order perturbation solutions are obtained and compared with a numerical solution to verify the perturbation solution. For the same spill quantity the combined model that consists of continuous and subsequent instantaneous model is necessary for small release times whereas the continuous model is only required for large release times. Additionally the combined release model is necessary for a small spill quantity at a fixed release time. These two release models are clearly distinguished using the perturbation solution.

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.

Metal hydrides are used for hydrogen storage. AlH3 shows a capacity to store about 10 wt% hydrogen. Its hydrogen is split-off in the temperature interval of 400–500 K. On dehydrogenation a nano-structured Al material emerges with specific surfaces up to 15–20 m2/g. The surface areas depend on the heating rate because of a temperature dependent crystallite growth. The resulting Al oxidizes up to 20–25% weight on air access forming an alumina passivation layer of 3–4 nm thickness on all exposed surfaces. The heat released from this Al oxidation induces a high risk to this type of hydrogen storage if the containment might be destroyed accidentally. The kinetics of the dehydrogenation and the subsequent oxidation is investigated by methods of thermal analysis. A reaction scheme is confirmed which consists of a starting Avrami-Erofeev mechanism followed by formal 1st order oxidation on unlimited air access. The kinetic parameters activation energies and pre-exponentials are evaluated and can be used to calculate the reaction progress. Together with the heat of the Al oxidation the overall heat release and the related rate can be estimated.

Sandia National Laboratories has worked with stakeholders and original equipment manufacturers (OEMs) to develop scientific data that can be used to create risk-informed hydrogen codes and standards for the safe operation of indoor hydrogen fuel-cell forklifts. An important issue is the possibility of an accident inside a warehouse or other enclosed space where a release of hydrogen from the high-pressure gaseous storage tank could occur. For such scenarios computational fluid dynamics (CFD) simulations have been used to model the release and dispersion of gaseous hydrogen from the vehicle and to study the behavior of the ignitable hydrogen cloud inside the warehouse or enclosure. The overpressure arising as a result of ignition and subsequent deflagration of the hydrogen cloud within the warehouse has been studied for different ignition delay times and ignition locations. Both ventilated and unventilated warehouses have been considered in the analysis. Experiments have been performed in a scaled warehouse test facility and compared with simulations to validate the results of the computational analysis.