Publications

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

A real-size calculation is performed for high-pressure hydrogen release in a tube using the axisymmetric Navier–Stokes equations with the full hydrogen chemistry. A Harten–Yee-type total variation diminishing scheme and point-implicit method are used to integrate the governing equations. The calculated real-size results show that the leading shock wave velocity is similar to that calculated using a smaller tube. The mixing process and ignition behaviour of high-pressure hydrogen are explained in detail; the velocity shear layer and Kelvin–Helmholtz instability are the main causes of mixing of hydrogen with air and ignition in the high-temperature region behind the leading shock wave.

Turbulence is a key aspect in hydrogen explosions. Unfortunately only limited experimental data is available and the current understanding of flame turbulence interactions is too limited to permit safe predictions. New experimental data are presented in which the flame trajectory and pressure history are interpreted for unconfined explosions of H2/O2/N2 clouds of 7 m3. The intensity of the turbulence is varied between 0 and 5 m/s and the integral scale of the turbulence is on the order of 10 cm which is at least an order of magnitude larger than lab scale.

Experiments are described in which hydrogen was released at the center of the floor of a real-scale enclosure having dimensions of a typical two-car residential garage. Real-time hydrogen concentrations were monitored at a number of locations. The hydrogen/air mixtures were ignited at pre-determined local volume fractions ranging from 8% to 29%. The combustion behavior and structural effects were monitored using combinations of high-speed pressure transducers and ionization gauges standard thermocouples hydrogen sensors and digital infrared and high-speed video cameras. Experiments were performed both for empty garages and garages with conventional automobiles parked above the hydrogen release location.

In the present study the diffusion process of hydrogen leaking from a FCV (Fuel Cell Vehicle) in an underground parking garage is analyzed by numerical simulations in order to assess the risk of a leakage accident. The temporal and spatial evolution of the hydrogen concentration as well as the flammable region in the parking garage was predicted numerically. The effects of the leakage flow rate and an additional ventilation fan were investigated to evaluate the ventilation performance to relieve the accumulation of the hydrogen gas. The volume of the flammable region shows a non-linear growth in time and rapidly increases eventually. The present numerical analysis can provide a physical insight and quantitative data for safety of various hydrogen applications.

We present an experimental study on the dispersion of helium in an enclosure of 1 m3 with natural ventilation through one vent. Three vent geometries have been studied. Injection parameters have been varied so that the injection Richardson number ranges from 2·10−6 to 9 and the volume Richardson number which gives the ability of the release to mix the enclosure content ranges from 8·10−4 to 900. It has been found that the vertical distribution of helium volume fraction can exhibit significant gradient. Nevertheless the results are compared to the simple analytical model based on the homogenous mixture hypothesis which gives fairly good estimates of the maximum helium volume fraction.

In this paper a study on the comparison between the different methodologies for the determination of the safety distances proposed by Standard Organizations and national Regulations is presented. The application of the risk-informed approach is one of the methodologies used for the determination of safety distances together with the risk-based approach. One of the main differences between the various methodologies is the risk criterion chosen. In fact a critical point is which level of risk should be used and then which are the harm events that must be considered. The harm distances are evaluated for a specified leak diameter that is a consequence of some parameters used in the various methodologies. The values of the safety distances proposed by Standard Organizations and national Regulations are a demonstration of the different approaches of the various methodologies especially in the choice of the leak diameter considered.

During the current global financial crisis the term “Risk Management” is often heard. Just as the causes for the financial problems are elusive so is a complete definition of what Risk Management means. The answer is highly dependent upon your perceptions of “risk” and your appetite for assuming risks. The proposed paper will explore these issues with some brief case studies as they apply to hydrogen industrial applications hydrogen refuelling stations and fuel cell technologies for distributed generation.

Specifically the paper will identify the various risk exposures from the perspective of the project developers original equipment suppliers end users project funding sources and traditional insurance providers. What makes this evaluation intriguing is that it is a mixed bag of output capacities Combine Heat & Power (CHP) potential and technology maturity. Therefore the application considerations must be part of any overall Risk Management program.

An increase in the number of hydrogen-fuelled applications in the marketplace will require a better understanding of the potential for fires and explosion associated with the unintended release of hydrogen within a structure. Predicting the temporally evolving hydrogen concentration in a structure with unknown release rates leak sizes and leak locations is a challenging task. A simple analytical model was developed to predict the natural and forced mixing and dispersion of a buoyant gas released in a partially enclosed compartment with vents at multiple levels. The model is based on determining the instantaneous compartment over-pressure that drives the flow through the vents and assumes that the helium released under the automobile mixes fully with the surrounding air. Model predictions were compared with data from a series of experiments conducted to measure the volume fraction of a buoyant gas (at 8 different locations) released under an automobile placed in the center of a full-scale garage (6.8 m × 5.4 m × 2.4 m). Helium was used as a surrogate gas for safety concerns. The rate of helium released under an automobile was scaled to represent 5 kg of hydrogen released over 4 h. CFD simulations were also performed to confirm the observed physical phenomena. Analytical model predictions for helium volume fraction compared favourably with measured experimental data for natural and forced ventilation. Parametric studies are presented to understand the effect of release rates vent size and location on the predicted volume fraction in the garage. Results demonstrate the applicability of the model to effectively and rapidly reduce the flammable concentration of hydrogen in a compartment through forced ventilation.

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

The accidents that hydrogen ignites without ignition source are reported in several cases which phenomenon is called “auto-ignition.” Since the use of high pressure hydrogen will be increased for the hydrogen society it must be necessary to understand auto-ignition mechanism in detail to prevent such accidents. In this study we performed three-dimensional numerical simulations to clarify the autoignition mechanism using the three-dimensional compressive Navier-Stokes equations and a hydrogen chemical reaction model including nine species and twenty elementary reactions. We focus on the effects of the shape of the cross-section on the hydrogen auto-ignition mechanism applying for a rectangular and cylindrical tube. The results obtained indicate that the Richtmyer-Meshukov instability involves these auto-ignition.

The use of high-fidelity simulation methods based on large-eddy simulation (LES) are proving useful for understanding and mitigating the safety hazards associated with hydrogen releases from nuclear power plants. However accurate modelling of turbulent premixed hydrogen flames via LES can require very high resolution to capture both the large-scale turbulence and its interaction with the flame fronts. Standard meshing strategies can result in impractically high computational costs especially for the thin fronts of hydrogen flames. For these reasons the use of a recently formulated integral length scale approximation (ILSA) subfilter-scale model in combination with an efficient anisotropic block-based adaptive mesh refinement (AMR) technique is proposed and examined herein for performing LES of turbulent premixed hydrogen flames. The anisotropic AMR method allows dynamic and solution-dependent resolution of flame fronts and the grid-independent properties of the ILSA model ensure that numerical errors associated with implicitly-filtered LES techniques in regions with varying resolution are avoided. The combined approach has the potential to allow formally converged LES solutions (direct numerical simulation results are typically reached in the limit of very fine meshes with standard subgrid models). The proposed LES methodology is applied to combustion simulations of lean premixed hydrogen-air mixtures within closed vessels: a problem relevant to hydrogen safety applications in nuclear facilities. A progress variable-based method with a multi-phenomena burning velocity model is used as the combustion model. The present simulation results are compared to the available experiment data for several previously studied THAI vessel cases and the capabilities of the proposed LES approach are assessed.

Hydrogen absorption into steel during atmospheric corrosion has been of a strong concern during last decades. It is technically important to investigate if hydrogen absorbed under atmospheric exposure conditions can significantly affect mechanical properties of steels. The present work studies changes of mechanical properties of dual phase (DP) advanced high strength steel specimens with sodium chloride deposits during corrosion in humid air using Slow Strain Rate Test (SSRT). Additional annealed specimens were used as reference in order to separate the possible effect of absorbed hydrogen from that of corrosion deterioration. Hydrogen entry was monitored in parallel experiments using hydrogen electric resistance sensor (HERS) and thermal desorption mass spectrometry (TDMS). SSRT results showed a drop in elongation and tensile strength by 42% and 6% respectively in 27 days of atmospheric exposure. However this decrease cannot be attributed to the effect of absorbed hydrogen despite the increase in hydrogen content with time of exposure. Cross-cut analysis revealed considerable pitting which was suggested to be the main reason for the degradation of mechanical properties

Efficient storage of hydrogen is crucial for the success of hydrogen energy markets (early markets as well as transportation market). Hydrogen can be stored either as a compressed gas a refrigerated liquefied gas a cryo-compressed gas or in hydrides. This paper gives an overview of hydrogen storage technologies and details the specific issues and constraints related to the materials behaviour in hydrogen and conditions representative of hydrogen energy uses. It is indeed essential for the development of applications requiring long-term performance to have good understanding of long-term behaviour of the materials of the storage device and its components under operational loads.

The unconfined release of high-pressure hydrogen can create a large flammable jet with the potential to generate significant damage. To properly understand the separation distances necessary to protect the immediate surroundings it is important to accurately assess the potential consequences. In these events the possibility for a detonation cannot be excluded and would generally result in the worst case scenario from the standpoint of damaging overpressure. The strong concentration gradients created by a jet release however raises the question of what portion of the flammable cloud should be considered. Often all of the fuel within the limits of fast-flame acceleration or even all of the fuel within the flammability range is considered which typically comprises the majority of the flammable cloud. In this work prior detonation studies are reviewed to illustrate the inherently unstable nature of detonations with a focus on the critical dimensions and concentration gradients that can support a propagating detonation wave. These criteria are then applied to the flammable cloud concentration distributions generated by an unconfined jet release of hydrogen. By evaluating these limits it is found that the portion of the flammable cloud that is likely to participate is significantly reduced. These results are compared with existing experimental data on the ignition of unconfined hydrogen releases and the peak pressures that were measured are consistent with a detonation of a mass of fuel that is equivalent to the model prediction for the mass of fuel within the detonable limits. This work demonstrates how the critical conditions for detonation propagation can be used to estimate the portion of a hydrogen release that could participates in a detonation and how these criteria can be readily incorporated into existing dispersion modelling approaches.

Simulation of hydrogen embrittlement (HE) requires a coupled approach; on one side the models describing hydrogen transport must account for local mechanical fields while on the other side the effect of hydrogen on the accelerated material damage must be implemented into the model describing crack initiation and growth. This study presents a review of coupled diffusion and cohesive zone modelling as a method for numerically assessing HE of a steel structure. While the model is able to reproduce single experimental results by appropriate fitting of the cohesive parameters there appears to be limitations in transferring these results to other hydrogen systems. Agreement may be improved by appropriately identifying the required input parameters for the particular system under study.

Link to document download on Royal Society Website 

The Fuel Cells and Hydrogen Joint Undertaking (FCH JU) has supported a range of initiatives in recent years designed to develop hydrogen fuel cell buses to a point where they can fulfil their promise as a mainstream zero emission vehicle for public transport.<br/>Within this study 90 different European cities and regions have been supported in understanding the business case of fuel cell bus deployment and across these locations. The study analyses the funding and financing for fuel cell bus deployment to make them become a mainstream zero emission choice for public transport providers in cities and regions across Europe. It also outlines possible solutions for further deployment of FC buses beyond the subsidised phase.<br/>In the light of the experience of the joint tender process in the UK and in Germany the study highlights best practices for ordering fuel cell buses. Other innovative instruments explored in other countries for the orders of large quantities of fuel cells buses are presented: Special Purpose Vehicles and centralised purchase office. Finally the study deeply analyses the funding and financing for fuel cell bus deployment to make them become a mainstream zero emission choice for public transport providers in cities and regions across Europe.

An underground mining ventilation testing facility (VTF) was designed and constructed at the HySA facility at the North-West University South Africa. The purpose was to evaluate risks associated with different hydrogen storage technologies in a confined environment. The work included initial calculations of hydrogen movement in specific spaces and the development of simulation tools to compare these modelled results with experimental work. For this purpose hydrogen sensors that could accurately measure hydrogen concentrations during a controlled hydrogen leak at the VTF were required. Hazardous hydrogen sensors capable of measuring >4% hydrogen are not readily available commercially. Typically hydrogen sensors rated for hazardous environments are designed for safety actions (e.g. activating emergency measures when hydrogen is detected) at concentrations of 8%. (Measuring concentrations higher than this is not required for commercial use hence there is no market for such sensors.) At the VTF it is necessary to be able to measure hydrogen concentrations >4% in order to obtain information on the flammable hydrogen concentrations at specified distances and orientations around a controlled hydrogen leak. Initial experimental work was conducted at low pressures resulting in very low hydrogen concentrations. Commercial available original equipment manufacturer (OEM) hydrogen sensors were capable of measuring 0.2% hydrogen which for the low pressures and gas flows here proved sufficient to enable us to make sensible conclusions. However higher pressures and gas flows are essential in practical use hence higher concentrations of hydrogen need to be measured. A custom sensor was developed by HySA while commercial sensors (OEM) were investigated. This work reports on the testing and evaluation of several hydrogen sensors. Results of initial ventilation tests are presented.

Ferrosilicon 75 a 50:50 mixture of silicon and iron disilicide has been activated toward hydrogen generation by processing using ball milling allowing a much lower concentration of sodium hydroxide (2 wt %) to be used to generate hydrogen from the silicon in ferrosilicon with a shorter induction time than has been reported previously. An activation energy of 62 kJ/mol was determined for the reaction of ball-milled ferrosilicon powder with sodium hydroxide solution which is around 30 kJ/mol lower than that previously reported for unmilled ferrosilicon. A series of composite powders were also prepared by ball milling ferrosilicon with various additives in order to improve the hydrogen generation properties from ferrosilicon 75 and attempt to activate the silicon in the passivating FeSi2 component. Three different classes of additives were employed: salts polymers and sugars. The effects of these additives on hydrogen generation from the reaction of ferrosilicon with 2 wt% aqueous sodium hydroxide were investigated. It was found that composites formed of ferrosilicon and sodium chloride potassium chloride sodium polyacrylate sodium polystyrene sulfonate-co-maleic acid or fructose showed reduced induction times for hydrogen generation compared to that observed for ferrosilicon alone and all but fructose also led to an increase in the maximum hydrogen generation rate. In light of its low cost and toxicity and beneficial effects sodium chloride is considered to be the most effective of these additives for activating the silicon in ferrosilicon toward hydrogen generation. Materials characterisation showed that neither ball milling on its own nor use of additives was successful in activating the FeSi2 component of ferrosilicon for hydrogen generation and the improvement in rate and shortening of the induction period was attributed to the silicon component of the mixture alone The gravimetric storage capacity for hydrogen in ferrosilicon 75 is therefore maintained at only 3.5% rather than the 10.5% ideally expected for a material containing 75% silicon. In light of these results ferrosilicon 75 does not appear a good candidate for hydrogen production in portable applications.

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

This document summarizes current hydrogen technologies and communicates the U.S. Department of Energy (DOE) Office of Fossil Energy's (FE's) strategic plan to accelerate research development and deploymnet of hydrogen technologies in the United States. It also describes ongoing FE hydrogen-related research and development (R&D). Hydrogen from fossil fuels is a versatile energy carrier and can play an important role in the transition to a low-carbon economy.

This report is prepared by thirty of the largest global car manufacturers oil and gas companies utilities equipment manufacturers NGOs governmental and clean energy organisations with the collaboration of the Fuel Cells and Hydrogen Joint Undertaking.<br/>The analysis compares the economics sustainability and performance of the vehicles and infrastructures needed to reach the 80% decarbonisation goal set by the<br/>European Union and is an unprecedented effort from industry and other stakeholders to analyse the role of the various new car-types in meeting this objective on the basis of proprietary industrial data.

Liquid hydrogen has been studied for use in vehicles. However during the charging process liquid hydrogen is lost as gas. Therefore it is necessary to estimate and reduce this loss and simulate the charging process. In this study the initial charging process of a vehicle liquid hydrogen tank under room temperature and atmospheric pressure conditions was numerically investigated. A transient thermal-fluid simulation with a phase-change model was performed to analyze variations in the volume pressure mass flow rate and temperature. The results showed that the process could be divided into three stages. In the first stage liquid hydrogen was actively vaporized at the inner wall surface of the storage tank. The pressure increased rapidly and liquid droplets were discharged into the vent pipe during the second stage. In the third stage the mass flow rates of liquid and hydrogen gas at the outlet showed significant fluctuations owing to complex momentum generated by the evaporation and charging flow. The temperatures of the inner and outer walls and insulation layer decreased significantly slower than that of the gas region because of its high heat capacity and insulation effect. The optimal structure should be further studied because the vortex stagnation and non-uniform cooling of the wall occurred near the inlet and outlet pipes.

Explosion venting is a frequently used measure to mitigate the consequence of gas deflagrations in closed environments. Despite the effort to predict the vent area needed to achieved the protection through engineering formulas and CFD tools work has still to be done to reliably predict the outcome of a vented gas explosion. Blind-prediction exercises recently published show a large spread in the prediction of both engineering formula than CFD tools. University of Pisa performed experimental tests in a 25 m3 facility in inhomogeneous conditions and with the presence of simple obstacles constituted by plates bolted to HEB beams. The present paper is aimed to share the results of hydrogen dispersion and deflagration tests and discuss the comparison of maximum peak overpressure generated with different blockage ratio and repeated obstacles sets. Description of the experimental set-up includes all the details deemed necessary to reproduce the phenomenon with a CFD tool.

Hydrogen is an essential element in the energy transition and can account for 24% of final energy demand and 5.4m jobs by 2050 says the new study by the FCH JU “Hydrogen Roadmap Europe: A sustainable pathway for the European Energy Transition“. Developed with input from 17 leading European industrial actors the study lays out a pathway for the large-scale deployment of hydrogen and fuel cells until 2050 and quantifies the associated socio-economic impacts.<br/>The report makes the case that hydrogen is required to address the challenges ahead. At scale decarbonisation of key segments such as the gas grid transport (particularly as relates to heavy duty vehicles) industrial processes that use high-grade heat and hydrogen as chemical feedstock require the use of hydrogen in large quantities.<br/>In addition the electrification of the economy and the large scale integration of intermittent renewable energy sources require large scale energy storage enabling seasonal storage and the efficient transport of clean energy across regions at low cost. Hydrogen is the only at scale technology capable of addressing all of these challenges.<br/>Importantly there will be important socio-economic and environmental benefits associated with this deployment such as an EUR 820B per year market and a total of 560Mt CO2 abated. The report lays out a roadmap for the ramp-up of market deployment across applications setting specific milestones between now and 2050. It also calls for a coordinated approach from policy makers industry and investors in order to achieve the 2-degree scenario.