Safe,long range,inexpensive and rapidly refuelable hydrogen vehicles with cryogenic pressure vessels

Hydrogen storage is often cited as the greatest obstacle to achieving a hydrogen economy free of environmental pollution and dependence on foreign oil. A compact high-pressure cryogenic storage system has promising features to the storage challenge associated with hydrogen-powered vehicles. Cryogenic pressure vessels consist of an inner vessel designed for high pressure (350 bar) insulated with reflective sheets of metalized plastic and enclosed within an outer metallic vacuum jacket. When filled with pressurized liquid hydrogen, cryogenic pressure vessels become the most compact form of hydrogen storage available. A recent prototype is the only automotive hydrogen vessel meeting both Department of Energy's 2017 weight and volume targets. When installed onboard an experimental vehicle, a cryogenic pressure vessel demonstrated the longest driving distance with a single H₂ tank (1050 km). In a subsequent experiment, the vessel demonstrated unprecedented thermal endurance: 8 days parking with no evaporative losses, extending to a month if the vehicle is driven as little as 8 km per day. Calculations indicate that cryogenic vessels offer compelling safety advantages and the lowest total ownership cost of hydrogen storage technologies. Long-term (∼10 years) vacuum stability (necessary for high performance thermal insulation) is the key outstanding technical challenge. Testing continues to establish technical feasibility and safety.     

Vehicular storage of hydrogen in insulated pressure vessels

This paper describes an alternative technology for storing hydrogen fuel onboard vehicles. Insulated pressure vessels are cryogenic capable vessels that can accept cryogenic liquid hydrogen, cryogenic compressed gas or compressed hydrogen gas at ambient temperature. Insulated pressure vessels offer advantages over conventional storage approaches. Insulated pressure vessels are more compact and require less carbon fiber than compressed hydrogen vessels. They have lower evaporative losses than liquid hydrogen tanks, and are lighter than metal hydrides.

The paper outlines the advantages of insulated pressure vessels and describes the experimental and analytical work conducted to verify that insulated pressure vessels can be safely used for vehicular hydrogen storage. Insulated pressure vessels have successfully completed a series of certification tests. A series of tests have been selected as a starting point toward developing a certification procedure. An insulated pressure vessel has been installed in a hydrogen fueled truck and tested over a six month period.     

Thermal design analysis of a 1 L cryogenic liquid hydrogen tank for an unmanned aerial vehicle

Thermal design analysis of a 1-L cryogenic liquid hydrogen storage tank without vacuum insulation for a small unmanned aerial vehicle was carried out in the present study. To prevent excess boil-off of cryogenic liquid hydrogen, the storage tank consisted of a 1-L inner vessel, an outer vessel, insulation layers and a vapor-cooled shield. For a cryogenic storage tank considered in this study, the appropriate heat inleak was allowed to supply the boil-off gas hydrogen to a proton electrolyte membrane fuel cell as fuel. In an effort to accommodate the hydrogen mass flow rate required by the fuel cell and to minimize the storage tank volume, a thermal analysis for various insulation materials was implemented here and their insulation performances were compared. The present thermal analysis showed that the Aerogel thermal insulations provided outstanding performance at the non-vacuum atmospheric pressure condition. With the Aerogel insulation, the tank volume for storing 1-L liquid hydrogen at 20 K could be designed within a storage tank volume of 7.2 L. In addition, it was noted that the exhaust temperature of boil-off hydrogen gas was mainly affected by the location of a vapor-cooled shield as well as thermal conductivity of insulation materials.     

High-density automotive hydrogen storage with cryogenic capable pressure vessels

LLNL is developing cryogenic capable pressure vessels with thermal endurance 5–10 times greater than conventional liquid hydrogen (LH₂) tanks that can eliminate evaporative losses in routine usage of (L)H₂ automobiles. In a joint effort BMW is working on a proof of concept for a first automotive cryo-compressed hydrogen storage system that can fulfill automotive requirements on system performance, life cycle, safety and cost. Cryogenic pressure vessels can be fueled with ambient temperature compressed gaseous hydrogen (CGH₂), LH₂ or cryogenic hydrogen at elevated supercritical pressure (cryo-compressed hydrogen, CcH₂). When filled with LH₂ or CcH₂, these vessels contain 2–3 times more fuel than conventional ambient temperature compressed H₂ vessels. LLNL has demonstrated fueling with LH₂ onboard two vehicles. The generation 2 vessel, installed onboard an H₂-powered Toyota Prius and fueled with LH₂ demonstrated the longest unrefueled driving distance and the longest cryogenic H₂ hold time without evaporative losses. A third generation vessel will be installed, reducing weight and volume by minimizing insulation thickness while still providing acceptable thermal endurance. Based on its long experience with cryogenic hydrogen storage, BMW has developed its cryo-compressed hydrogen storage concept, which is now undergoing a thorough system and component validation to prove compliance with automotive requirements before it can be demonstrated in a BMW test vehicle.     

Modeling of sudden hydrogen expansion from cryogenic pressure vessel failure

We have modeled sudden hydrogen expansion from a cryogenic pressure vessel. This model considers real gas equations of state, single and two-phase flow, and the specific “vessel within vessel” geometry of cryogenic vessels. The model can solve sudden hydrogen expansion for initial pressures up to 1210 bar and for initial temperatures ranging from 27 to 400 K. For practical reasons, our study focuses on hydrogen release from 345 bar, with temperatures between 62 K and 300 K. The pressure vessel internal volume is 151 L. The results indicate that cryogenic pressure vessels may offer a safety advantage with respect to compressed hydrogen vessels because i) the vacuum jacket protects the pressure vessel from environmental damage, ii) hydrogen, when released, discharges first into an intermediate chamber before reaching the outside environment, and iii) working temperature is typically much lower and thus the hydrogen has less energy. Results indicate that key expansion parameters such as pressure, rate of energy release, and thrust are all considerably lower for a cryogenic vessel within vessel geometry as compared to ambient temperature compressed gas vessels. Future work will focus on taking advantage of these favorable conditions to attempt fail-safe cryogenic vessel designs that do not harm people or property even after catastrophic failure of the inner pressure vessel.     

The storage performance of automotive cryo-compressed hydrogen vessels

Cryo-compressed hydrogen storage promises to deliver the highest system storage density leading to practical vehicles with range comparable to today's gasoline vehicles and fundamental cost and safety advantages. However, cryogenic vessels are complex systems, continuously drifting in thermodynamic space depending on use patterns, insulation performance, vessel characteristics, liquid hydrogen pump performance, and para-H₂ to ortho-H₂ conversion. In this paper, cryogenic vessel fill density results from a previous publication are extended to calculate system storage performance, including volumetric (gH₂/L), gravimetric (H₂ weight fraction), and vent losses over a broad range of conditions. The results confirm previous experiments and models indicating that cryogenic pressure vessels have maximum system density of all available storage technologies while avoiding vent losses in all but the most extreme situations. Design pressures in the range 250–350 bar seem most advantageous due to high system density and low weight and cost, although determining an optimum pressure demands a complete economic and functional analysis. Future insulation, vessel, and liquid hydrogen pump improvements are finally analyzed that, while not experimentally demonstrated to date, show promise of being feasible in the future as their level of technical maturity increases, leading to maximum H₂ storage performance for cryo-compressed storage. If proven feasible and incorporated into future cryogenic vessels, these improvements will enable 50 + gH₂/L system density at 10+% H₂ weight fraction.     

Mixing and warming of cryogenic hydrogen releases

Laboratory measurements were made on the concentration and temperature fields of cryogenic hydrogen jets. Images of spontaneous Raman scattering from a pulsed planar laser sheet were used to measure the concentration and temperature fields from varied releases. Jets with up to 5 bar pressure, with near-liquid temperatures at the release point, were characterized in this work. This data is relevant for characterizing unintended leaks from piping connected to cryogenic hydrogen storage tanks, such as might be encountered at a hydrogen fuel cell vehicle fueling station. The average centerline mass fraction was observed to decay at a rate similar to room temperature hydrogen jets, while the half-width of the Gaussian profiles of mass fraction were observed to spread more slowly than for room temperature hydrogen. This suggests that the mixing and models for cryogenic hydrogen may be different than for room temperature hydrogen. Results from this work were also compared to a one-dimensional (streamwise) model. Good agreement was seen in terms of temperature and mass fraction. In subsequent work, a validated version of this model will be exercised to quantitatively assess the risk at hydrogen fueling stations with cryogenic hydrogen on-site.     

Analysis of multilayered carbon fiber winding of cryo-compressed hydrogen storage vessel

In order to meet the hydrogen storage requirements of fuel cell vehicles, and improve the storage density of hydrogen, a cryo-compressed hydrogen storage method was proposed. The performance of cryo-compressed hydrogen storage vessel was analyzed in this paper. Based on the classical laminate theory and heat transfer solution, the stress and displacement of carbon fiber were precisely calculated to guarantee the cryo-compressed vessel severing in the cryogenic condition. Subsequently, the Tsai-Wu failure criterion was used to judge the failure of carbon fiber reinforced plastics layers. The stacking sequence, winding angle, comparison of the vessel's performance at room temperature and low temperature were conducted. The numerical results showed that the properties of storage vessel decreased at cryogenic condition, and the thickness of carbon fiber at cryogenic temperature at least increased by 47.06% than that at the room temperature. Mainly influence of low temperature on the cryo-compressed vessel were concentrated on the hoop stress of helical winding and the axial stress of hoop winding. For the vessel design, it is achievable to increase these two parts by using higher strength resin materials.     

The fill density of automotive cryo-compressed hydrogen vessels

Cryo-compressed hydrogen storage promises to deliver highest system storage density leading to fundamental cost and safety advantages. However, cryogenic vessels are complex systems, continuously drifting in thermodynamic space depending on use patterns, insulation performance, vessel characteristics, liquid hydrogen pump performance, and para-H₂ to ortho-H₂ conversion. This paper shows a comprehensive evaluation of all factors affecting cryogenic vessel fill density, in an effort to evaluate system performance vs. operational parameters over a broad range of conditions. The results confirm previous experiments and models indicating that cryogenic vessels have maximum fill density of all available storage technologies, and fill density is most sensitive to daily driving distance and insulation performance. It is finally predicted that para-H₂ to ortho-H₂ conversion will affect most automobiles, increasing fill density by up to 5.3%. In a future world dominated by cryogenic H₂ fueled vehicles, para-H₂ to ortho-H₂ conversion inside the vessel will be the closest contact an average person will have with quantum mechanics outside of consumer electronics.     

Development potentials for small mobile storage tanks with vacuum powder insulations

Vehicle cryofuel tanks for LNG and liquid hydrogen are currently multilayer vacuum superinsulated (MLVSI). MLVSI are known for thermal conductivities as low as 10⁻⁶W(mK)⁻¹ at cryogenic temperatures. Due to high system costs, these tanks burden the economy of cryofueled vehicles. In search of low tank costs, powdrous load-bearing insulations, applied to large storage and transport vessels today, were examined for their MLVSI-replacement potential.Thermal conductivities of some popular powders were measured to about 2–8 mW (m K)⁻¹ at zero and full external loads representing vacuum pressure enforced on the insulation layer. Furthermore, a transient simulation program was written to examine the influence of various operational parameters on powder insulated cryofuel tanks onboard passenger cars and trucks. The results were interpreted mainly for LNG fuel tanks with perspectives for liquid hydrogen.     

A landscape of hydride compounds for off-board refilling of transport vehicles

The authors compare the energy consumption of hydrogen cars (using fuel cells) with electric cars (using batteries) and conventional petrol cars finding that hydrogen cars are preferable to electric cars for long distances. They evaluate several types of hydrogen storage materials in terms of off-board refilling, in which hydrogen uptake takes place outside the vehicle. Literature values for enthalpy and entropy of formation etc. are used to calculate hydrogen densities, heat production and theoretical desorption temperature. Additionally, experimental literature values for temperature and pressure of (de)hydrogenation, kinetics and cycling stability are summarized. The results are discussed assuming that hydrogen refilling takes place in a replaceable tank outside the vehicle, which reduces the DOE requirements to high volumetric and gravimetric density, moderate release temperature, sufficiently fast release and high reversibility. They are fulfilled by materials like NaAlH₄, while even better performance can be expected from compounds like LiBH₄+MeH_x or Mg-Ti composites.     

燃料电池车车载储氢系统的技术发展与应用现状

综述了燃料电池车车载储氢系统技术，包括高压氢、液氢、金属氢化物、低温吸附、纳米碳管高压吸附以及液体有机氢化物等的研究进展及其车载应用现状。参照燃料电池车对车载储氢系统单位重量储氢密度与体积储氢密度的目标要求，对目前已应用和处于研发阶段的一些储氢技术的性能指标和存在问题进行了分析讨论。同时对目前该领域的若干新的研究报道，如超高压轻质复合容器、混合储氢容器、b.c．c．储氢合金、超级活性碳和“浆液”双相储氢等，也作了简要介绍。     

Hydrogen: The future cryofuel in internal combustion engines

The characteristics of cryogenic hydrogen, such as high density and considerable cooling effect, favor the fuel injection, the mixing process and thus the combustion process. In addition to the preferred use of liquid hydrogen due to its range per tank filling and low amount of mass for storage in the vehicle, the cryogenic characteristics of hydrogen provide significant advantages. In addition to engine operation with external mixture formation, considerable success was achieved with internal mixture formation with injection of cryogenic high pressure hydrogen. Only pressurization of cryogenic hydrogen can be accomplished without investing a considerable amount of engine power. Hybrid mixture formation, a proper combination of external and internal mixture formation with suitably pressurized cryogenic hydrogen, is very attractive with respect to power and torque as well as other positive characteristics under steady and intermittent operating conditions.The state of the art technology of liquid hydrogen represents a suitable base for large scale demonstration projects now. Additional aims of more intense R&D work relate to internal mixture formation and improved engine drivability, as well as utility vehicle application including trucks and buses. With respect to fuel costs there will be an increased demand in developing hydrogen production free from CO₂ emissions even from fossil sources such as crude oil or natural gas.     

Integration of a light mobility urban scale hydrogen refuelling station for cycling purposes in the transportation market

Road transportation consists of a significant contributor to total greenhouse gas emissions in developed countries. New alternative technologies in transportation such as electric vehicles aim to reduce substantially vehicle emissions, particularly in urban areas. Incentives of using two-wheel electric vehicles such as bicycles in big cities centres are promoted by local governments, and in fact, some countries are already trying to adopt this transition. An interesting case consists of the use of hydrogen fuel cells in such vehicles to increase their driving range under short refuelling times. To this end, this paper investigated the social and financial prospects of hydrogen infrastructure for city-oriented fuel cell electric vehicles such as bicycles. The results of the research indicated that a light mobility urban hydrogen refuelling station able to provide refuelling processes at pressures of 30 bar with a hydrogen fuel cost of 34.7 €/kgH₂ is more favourable compared to larger stations.     

Review on optimization design,failure analysis and non-destructive testing of composite hydrogen storage vessel

Composite hydrogen storage vessels have been increasingly applied to hydrogen fuel cell vehicles. This review focuses on optimization design, failure analysis and nondestructive testing for enhancing the safety of composites hydrogen storage vessels in service. The optimization designs of the composite vessel components help to improve the durability and strength of composite vessels subjected to burst pressure and fatigue loads. In complex service environments, composite vessels may suffer from various failure forms (burst failure, fatigue failure and impact failure) which involve different damage processes and influence factors. More importantly, this review discusses the applications of acoustic emission, digital image correlation, optical fiber in studying the residual performance (burst pressure and fatigue life) and damage modes of the composite vessel. It is expected that the combination of nondestructive testing techniques plays an increasingly important role in developing the composite vessel for structural health monitoring.     

Assessing the operation and different refuelling cost scenarios of a fuel cell electric bicycle under low-pressure hydrogen storage

The transition to low- or zero-emission vehicles in the transportation sector is a challenging task toward meeting the greenhouse gas emission targets set by the majority of countries. One way of achieving this goal is to utilise hydrogen gas via fuel cell electric vehicles. This paper investigates the operation, driving range and refuelling process of a fuel cell electric bicycle. The methodology applied includes an estimation of the bike's range under different routes and riders, the riders' opinions and a financial evaluation of the hydrogen fuel cost compared to other urban vehicle alternatives. The results showed a minimum median range-to-energy consumption ratio of 20.5 km/kWh, while the maximum hydrogen cost was found to reach 0.025 €/km when refuelling the hydrogen bicycle in an autonomous hydrogen station. The outcome of this study indicates that the introduction of light-duty hydrogen vehicles in urban transportation may adequately meet the average daily driving distance of city residents.     

Modelling and simulation of a zero-emission hybrid power plant for a domestic ferry

This paper presents a simulation tool for marine hybrid power-plants equipped with polymer exchange membrane fuel cells and batteries. The virtual model, through the combination of operational data and dynamically modelled subsystems, can simulate power-plants of different sizes and configurations, in order to analyze the response of different energy management strategies. The model aims to replicate the realistic behavior of the components included in the vessel's grid, to asses if the hardware selected by the user is capable of delivering the power set-point requested by the energy management system. The model can then be used to optimize key factors such as hydrogen consumption. The case study presented in the paper demonstrates how the model can be used for the evaluation of a retrofitting operation, replacing a diesel electric power-plant with fuel cells and batteries. The vessel taken into consideration is a domestic ferry, operating car and passenger transport in Denmark. The vessel is outfitted with a diesel electric plant and an alternative hybrid power-plant is proposed. The hybrid configuration is tested using the model in a discrete time-domain.     

Hydrogen decompression analysis by multi-stage Tesla valves for hydrogen fuel cell

Hydrogen fuel cell is an ideal power source for electric vehicles. For a hydrogen fuel cell electric vehicle, the hydrogen is reserved in a high pressure level to promote the recharge mileage while relatively low-pressure hydrogen is demanded for proper functioning of the fuel cell stack, so that decompression of hydrogen is needed before hydrogen flowing into the fuel cell. With a reverse flow through Tesla valves, there appears a large pressure drop between the inlet and outlet, which can be used for hydrogen decompression nicely. However, a single-stage Tesla valve cannot meet the pressure drop requirement, so multi-stage Tesla valves are utilized. In this paper, numerical simulations of reversed hydrogen flow through multi-stage Tesla valves are carried out. The stage number of multi-stage Tesla valves and the inlet/outlet pressure ratio are both studied, and the distributions of temperature, pressure, and velocity inside multi-stage Tesla valves are all investigated. Results show that as the stage number increases or the inlet/outlet pressure ratio decreases, the pressure and the velocity inside multi-stage Tesla valves decrease, and the less the stage number, the more possibility for the velocity higher than local acoustic speed. Besides, a power-law relationship between the flow rate, the stage number and pressure ratio is summarized.     

System design and control strategy of the vehicles using hydrogen energy

This paper presented a system design review of fuel cell hybrid vehicle. Fuel supply, hydrogen storage, DC/DC converters, fuel cell system and fuel cell hybrid electric vehicle configurations were also reviewed. We explained the difference of fuel supply requirement between hydrogen vehicle and conventional vehicles. Three different types of hydrogen storage system for fuel supply are briefly introduced: high pressure, liquid storage and metal oxides storage. Considering of the potential risk of explosion, a security hydrogen storage system is designed to restrict gas pressure in the safe range. Due to the poor dynamic performance of fuel cells, DC/DC converters were added in hybrid vehicle system to improve response to the changes of power demand. Requirements that in order to select a suitable DC/DC converter for fuel-cell vehicles design were listed. We also discussed three different configurations of fuel-cell hybrid vehicles: “FC + B”, “FC + C”, and “FC + B + C”, describing both disadvantages and advantages. “FC + B + C” structure has a better performance among three structures because it could provide or absorb peak current during acceleration and emergency braking. Finally, the energy management strategies of fuel cell and were proposed and the automotive energy power requirement of an application example was calculated.     

Vacuum generation by hydrogen permeation to atmosphere through austenitic and nickel-base-alloy vessel walls at temperatures from 573 K to 773 K

The permeation of hydrogen through metals is of great concern in hydrogen containment systems. In this study, hydrogen contained in seamless coiled tube vessels made of SUS 316L and Inconel 625 permeated the vessel walls at temperatures from 573 K to 773 K, and the decreasing interior pressure of the vessels was monitored for an extended period to characterize the behavior of the pressure change. It was found that the pressure became lower than the surrounding atmospheric pressure, and the vessels reached a vacuum. Hydrogen permeabilities through SUS 316L and Inconel 625 were determined from the pressure drop measurements. In order to ensure the reliability of the measurements, the permeabilities were also determined with a gas chromatograph that measured the concentration of hydrogen completely permeating the vessel wall. The permeabilities obtained with the two methods were in good agreement with each other. The pressure drop behavior was compared to, and found to be consistent with, theoretical calculations performed using the obtained permeabilities based on Fick’s law of diffusion.