Safety

The  storage  of  hydrogen  poses  inherent  weight  volume  and  safety  obstacles.  An  innovative technology which allows for the storage of hydrogen in thin sealed glass capillaries ensures the safe infusion storage and controlled release of hydrogen gas under pressures up to 100 MPa. Glass is a non-flammable material which also guarantees high burst pressures. The pressure resistance of single and multiple capillaries has been determined for different glass materials. Borosilicate capillaries have been proven to have the highest pressure resistance and have therefore been selected for further series of  advanced testing.  The innovative  storage  system  is  finally  composed of  a  variable number  of modules. As such in the case of the release of hydrogen this modular arrangement allows potential hazards to be reduced to a minimum. Further advantage of a modular system is the arrangement of single modules in every shape and volume dependent on the final application. Therefore the typical locations of storage systems e.g. the rear of cars can be modified or shifted to places of higher safety and not directly involved in crashes. The various methods of refilling and releasing capillaries with compressed hydrogen the increase of burst pressures through pre-treatment as well as the theoretical analysis and  experimental results of  the resistance  of glass  capillaries will further  be discussed  in detail.

Vehicular use of hydrogen is the first attempt to apply hydrogen energy in consumers’ environment in large scale and has raised safety concerns in both public authorities and private bodies such as fire services and insurance companies. This paper analyzes typical accident progressions of hydrogen fuel cell vehicles in a road collision accident. Major hydrogen consequences including impinging jet fires and catastrophic tank ruptures are evaluated separately in terms of accident duration and hazard distances. Results show that in a 70 MPa fuel cell car accident the hazards associated with hydrogen releases would normally last for no more than 1.5 min due to the empty of the tank. For the safety of general public a perimeter of 100 m is suggested in the accident scene if no hissing sound is heard. However the perimeter can be reduced to 10 m once the hissing sound of hydrogen release is heard. Furthermore risks of fatalities injuries and damages are all quantified in financial terms to assess the impacts of the accident. Results show that costs of fatalities and injuries contribute most to the overall financial loss indicating that the insurance premium of fatalities and injuries should be set higher than that of property loss.

In this work we evaluate the consequences of the combustion of a stoichiometric mixture of hydrogen-air on a mechanical device which can be considered as a long tube. In order to choose the most dangerous combustion regime for the mechanical device we devote a particular attention to the investigation of the 1D deflagration-to-detonation transition. Then once established the most dangerous combustion regime we compute the reacting  flow and the stress and strain in the mechanical device. Analyses are performed using both semi-analytical solutions and Europlexus a computer program for the simulation of  fluid-structure systems under transient dynamic loading.

In a near future with an increasing use of hydrogen as an energy vector gaseous hydrogen transport as well as high capacity storage may imply the use of high strength steel pipelines for economical reasons. However such materials are well known to be sensitive to hydrogen embrittlement (HE). For safety reasons it is thus necessary to improve and clarify the means of quantifying embrittlement. The present paper exposes the changes in mechanical properties of a grade API X80 steel through numerous mechanical tests i.e. tensile tests disk pressure test fracture toughness and fatigue crack growth measurements WOL tests performed either in neutral atmosphere or in high-pressure of hydrogen gas. The observed results are then discussed in front of safety considerations for the redaction of standards for the qualification of materials dedicating to hydrogen transport.

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

Hydrogen gas explosions in homogeneous reactive mixtures have been widely studied both experimentally and numerically. However in practice combustible mixtures are usually inhomogeneous and subject to both vertical and horizontal concentration gradients. There is still very limited understanding of the hydrogen explosion characteristics in such situations. The present numerical investigation aims to study the effect of mixture concentration gradient on the process of Deflagration to Detonation Transition and the effect of different hydrogen concentration gradient in the obstructed channel of hydrogen/air mixtures. An obstructed channel with 30% blockage ratio (BR=30) and three different average hydrogen concentrations of 20 % 30% and 35% have been considered using a specially developed density-based solver within the OpenFOAM toolbox. A high-resolution grid was built with the using adaptive mesh refinement technique providing 10 grid points in half reaction length. The numerical results are in reasonably good agreement with the experimental  observations [1]. These studies show that the concentration gradient has a considerable effect on the accelerated flame tip speed and the location of transition to detonation in the obstructed channel. In all the three cases the first localised explosion occurred near the bottom wall where the shock and flame interacted and the mixture was most lean; and the second localised explosion occurred at the top wall due to the reflection of shock and flame front and later develops to form the leading detonation wave. The increase in the fuel concentration was found to increase the flame acceleration (FA) and having a faster transition to detonation.

A large number of natural gas vehicles (NGV) with composite cylinders run in the world. In order to store hydrogen using the composite cylinder has also reached commercialization for the hydrogen fuel cell vehicle (FCV) which is been developing on ECO Energy. Under these increasing circumstances the most important issue is that makes sure of safety of the hydrogen composite cylinder. In case of the composite cylinder a standards to verify the safety of cylinders obey several country's standards. For NGV ISO 11439 has adopted as international standards but for FCV it has been still developing and there is only ISO/TS 15869 as international technical standards. In contents of international standards the fire test is the weakest part. The fire test is that the pressure relief valves (PRD) normally operate or not in order to prevent cylinders bursting when a vehicle is covered by fire. However with present standards there is no method to check the problem from vehicles in local flame. This study includes fire test results that have been performed to establish the fire-test standards.

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

Hydrogen behavior at elevated pressures and temperatures was intensively studied by numerous investigators. Nevertheless there is a lack of experimental data on hydrogen ignition and combustion at reduced sub-atmospheric pressures. Such conditions are related to the facilities operating under vacuum or sub-atmospheric conditions for instance like ITER vacuum vessel. Main goal of current work was an experimental evaluation of such fundamental properties of hydrogen–air mixtures as flammability limits and laminar flame speed at sub-atmospheric pressures. A spherical explosion chamber with a volume of 8.2 dm3 was used in the experiments. A pressure method and high-speed camera combined with schlieren system for flame visualization were used in this work. Upper and lower flammability limits and laminar flame velocity have been experimentally evaluated in the range of 4–80% hydrogen in air at initial pressures 25–1000 mbar. An extraction of basic flame properties as Markstein length overall reaction order and activation energy was done from experimental data on laminar burning velocity.

We report the development and testing of a novel hydrogen sensor that shows a very peculiar response to hydrogen exposure due to its micro-structured palladium surface. The fabrication of the wrinkled Pd surface is obtained using an innovative fast and cheap technique based on the deposition of a thin Pd film on to a thermo-retractable polystyrene sheet that shrinks to 40% of its original size when heated. The buckling of the Pd surface induced by shrinking of the substrate produces nano and micro-wrinkles on the sensor surface. The micro-structured sensor surface is very stable even after repeated hydrogen sorption/desorption cycles. The hydrogen sensing mechanism is based on the transitory absorption of hydrogen atoms into the Pd layer leading to the reversible change of its electrical resistance. Interestingly depending on hydrogen concentration the proposed sensor shows the concurrent effect of both the usually described behaviors of increase or decrease of resistance related to different phenomena occurring upon hydrogen exposure and formation of palladium hydride. The study reports and discusses evidences for an activation threshold of hydrogen concentration in air switching the behavior of sensor performances from e.g. poor negative to large positive sensitivity and from slow to fast detection.