H2 refueling assessment of composite storage tank for fuel cell vehicle

Hydrogen as compressed gas is a promising option for zero-emission fuel cell vehicle. The fast and efficient refueling of high pressure hydrogen can provide a convenient platform for fuel cell vehicles to compete with conventional gasoline vehicles. This paper reports the finding of adiabatic simulation of the refueling process for Type IV tank at nominal working pressure of 70 MPa with considering the station refueling conditions. The overall heat transfer involved in refueling process was investigated by heat capacity model based on MC method defined by SAE J2601. The simulation results are validated against experimental data of European Commission's Gas Tank Testing Facility at Joint Research Centre (GasTef JRC), Netherlands. The results confirmed that end temperature and state of charge significantly depends on refueling parameters mainly supply hydrogen temperature and filling rate.     

Impact of hydrogen SAE J2601 fueling methods on fueling time of light-duty fuel cell electric vehicles

Hydrogen fuel cell electric vehicles (HFCEVs) are zero-emission vehicles (ZEVs) that can provide drivers a similar experience to conventional internal combustion engine vehicles (ICEVs), in terms of fueling time and performance (i.e. power and driving range). The Society of Automotive Engineers (SAE) developed fueling protocol J2601 for light-duty HFCEVs to ensure safe vehicle fills while maximizing fueling performance. This study employs a physical model that simulates and compares the fueling performance of two fueling methods, known as the “lookup table” method and the “MC formula” method, within the SAE J2601 protocol. Both the fueling methods provide fast fueling of HFCEVs within minutes, but the MC formula method takes advantage of active measurement of precooling temperature to dynamically control the fueling process, and thereby provides faster vehicle fills. The MC formula method greatly reduces fueling time compared to the lookup table method at higher ambient temperatures, as well as when the precooling temperature falls on the colder side of the expected temperature window for all station types. Although the SAE J2601 lookup table method is the currently implemented standard for refueling hydrogen fuel cell vehicles, the MC formula method provides significant fueling time advantages in certain conditions; these warrant its implementation in future hydrogen refueling stations for better customer satisfaction with fueling experience of HFCEVs.     

Determining correlations between final hydrogen temperature and refueling parameters from experimental and numerical data

During the hydrogen filling process, the excessive temperature rise may cause the hydrogen storage tank to fail. Therefore, preventing the temperature from rising too high is an important guarantee for the safety of the hydrogen storage cylinder. The analytical solution of a single-zone thermodynamic model for hydrogen refueling is obtained. Based on the analytical solution of the final hydrogen temperature derived from the hydrogen filling theoretical model, the relationship among the final hydrogen temperature and the initial temperature and the inlet temperature and the ambient temperature is obtained. The model is used to achieve correlations coefficients among the above parameters. Data of Type III 40L tank and Type IV 29L tank used in the model are from the experiment, and data of Type III 25L tank and Type IV 174L tank are from the simulation. The results show that our analytical solution is applicable for determining correlations between final hydrogen temperature and refueling parameters from experimental and numerical data. Our analytical solution is more accurate than the reduced model reported in reference. At the same time, the effects of the initial temperature and the inlet temperature on the final temperature are stronger in Type IV tank than in the Type III tank. This study may provide guides for improving hydrogen refueling standards.     

Liquid pump-enabled hydrogen refueling system for heavy duty fuel cell vehicles: Pump performance and J2601-compliant fills with precooling

We have developed a hydrogen (H₂) refueling solution capable of delivering precooled, compressed gaseous hydrogen for heavy duty vehicle (HDV) refueling applications. The system uses a submerged pump to deliver pressurized liquid H₂ from a cryogenic storage tank to a dispensing control loop that vaporizes the liquid and adjusts the pressure and temperature of the resulting gas to enable refueling at 35 MPa and temperatures as low as ?40 °C. A full-scale mobile refueler was fabricated and tested over a 6-month campaign to validate its performance. We report results from tests involving a total of 9000 kg of liquid H₂ pumped and 1350 filling cycles over a range of conditions. Notably, the system was able to repeatably complete multiple, back-to-back 30 kg filling cycles in under 6 min each, in full compliance with the SAE J2601-2 standard, demonstrating its potential for rapid-throughput HDV refueling applications.     

Thermodynamic modeling of hydrogen refueling for heavy-duty fuel cell buses and comparison with aggregated real data

The foreseen uptake of hydrogen mobility is a fundamental step towards the decarbonization of the transport sector. Under such premises, both refueling infrastructure and vehicles should be deployed together with improved refueling protocols. Several studies focus on refueling the light-duty vehicles with 10 kg_H2 up to 700 bar, however less known effort is reported for refueling heavy-duty vehicles with 30–40 kg_H2 at 350 bar. The present study illustrates the application of a lumped model to a fuel cell bus tank-to-tank refueling event, tailored upon the real data acquired in the 3Emotion Project. The evolution of the main refueling quantities, such as pressure, temperature, and mass flow, are predicted dynamically throughout the refueling process, as a function of the operating parameters, within the safety limits imposed by SAE J2601/2 technical standard. The results show to refuel the vehicle tank from half to full capacity with an Average Pressure Ramp Rate (APRR) equal to 0.03 MPa/s are needed about 10 min. Furthermore, it is found that the effect of varying the initial vehicle tank pressure is more significant than changing the ambient temperature on the refueling performances. In conclusion, the analysis of the effect of different APRR, from 0.03 to 0.1 MPa/s, indicate that is possible to safely reduce the duration of half-to-full refueling by 62% increasing the APRR value from 0.03 to 0.08 MPa/s.     

Optimization of hydrogen vehicle refueling via dynamic simulation

A dynamic model has been developed to analyze and optimize the thermodynamics and design of hydrogen refueling stations. The model is based on Dymola software and incorporates discrete components. Two refueling station designs were simulated and compared. The modeling results indicate that pressure loss in the vehicle's storage system is one of the main factors determining the mass flow and peak cooling requirements of the refueling process. The design of the refueling station does not influence the refueling of the vehicle when the requirements of the technical information report J2601 from Society of Automotive Engineers are met. However, by using multiple pressure stages in the tanks at the refueling station (instead of a single high-pressure tank), the total energy demand for cooling can be reduced by 12%, and the compressor power consumption can be reduced by 17%. The time between refueling is reduced by 5%, and the total amount of stored hydrogen at high pressure is reduced by 20%.     

Estimation of final hydrogen temperature from refueling parameters

Compressed hydrogen storage is currently widely used in fuel cell vehicles due to its simplicity in tank structure and refueling process. For safety reason, the final gas temperature in the hydrogen tank during vehicle refueling must be maintained under a certain limit, e.g., 85 °C. Many experiments have been performed to find the relations between the final gas temperature in the hydrogen tank and refueling conditions. The analytical solution of the hydrogen temperature in the tank can be obtained from the simplified thermodynamic model of a compressed hydrogen storage tank, and it serves as function formula to fit experimental temperatures. From the analytical solution, the final hydrogen temperature can be expressed as a weighted average form of initial temperature, inflow temperature and ambient temperature inspired by the rule of mixtures. The weighted factors are related to other refueling parameters, such as initial mass, initial pressure, refueling time, refueling mass rate, average pressure ramp rate (APRR), final mass, final pressure, etc. The function formula coming from the analytical solution of the thermodynamic model is more meaningful physically and more efficient mathematically in fitting experimental temperatures. The simple uniform formula, inspired by the concept of the rule of mixture and its weighted factors obtained from the analytical solution of lumped parameter thermodynamics model, is representatively used to fit the experimental and simulated results in publication. Estimation of final hydrogen temperature from refueling parameters based on the rule of mixtures is simple and practical for controlling the maximum temperature and for ensuring hydrogen safety during fast filling process.     

Single-tank storage versus multi-tank cascade system in hydrogen refueling stations for fuel cell buses

Many countries in Europe are investing in fuel cell bus technology with the expected mobilization of more than 1200 buses across Europe in the following years. The scaling-up will make indispensable a more effective design and management of hydrogen refueling stations to improve the refueling phase in terms of refueling time and dispensed quantity while containing the investment and operation costs. In the present study, a previously developed dynamic lumped model of a hydrogen refueling process, developed in MATLAB, is used to analyze tank-to-tank fuel cell buses (30–40 kg_H2 at 350 bar) refueling operations comparing a single-tank storage with a multi-tank cascade system. The new-built Aalborg (DK) hydrogen refueling station serves as a case study for the cascade design. In general, a cascading refueling approach from multiple storage tanks at different pressure levels provides the opportunity for a more optimized management of the station storage, reducing the pressure differential between the refueling and refueled tanks throughout the whole refueling process, thus reducing compression energy. This study demonstrates the validity of these aspects for heavy-duty applications through the technical evaluation of the refueling time, gas heating, compression energy consumption and hydrogen utilization, filling the literature gap on cascade versus single tank refueling comparison. Furthermore, a simplified calculation of the capital and operating expenditures is conducted, denoting the cost-effectiveness of the cascade configuration under study. Finally, the effect of different pressure switching points between the storage tanks is investigated, showing that a lower medium pressure usage reduces the compression energy consumption and increases the station flexibility.     

Review on the research of hydrogen storage system fast refueling in fuel cell vehicle

A comprehensive review of the hydrogen storage systems and investigations performed in search for development of fast refueling technology for fuel cell vehicles are presented. Nowadays, hydrogen is considered as a good and promising energy carrier and can be stored in gaseous, liquid or solid state. Among the three ways, high pressure (such as 35 MPa or 70 MPa) appears to be the most suitable method for transportation due to its technical simplicity, high reliability, high energy efficiency and affordability. However, the refueling of high pressure hydrogen can cause a rapid increase of inner temperature of the storage cylinder, which may result not only in a decrease of the state of charge (SOC) but also in damages to the tank walls and finally to safety problems. In this paper, the theoretical analysis, experiments and simulations on the factors related to the fast refueling, such as initial pressure, initial temperature, filling rate and ambient temperature, are reviewed and analyzed. Understanding the potential relationships between these parameters and the temperature rise may shed a light in developing novel controlling strategies and innovative routes for hydrogen tank fast filling.     

Liquid pump-enabled hydrogen refueling system for heavy duty fuel cell vehicles: Fuel cell bus refueling demonstration at Stark Area Regional Transit Authority (SARTA)

We have demonstrated a hydrogen (H₂) refueling solution capable of delivering precooled, compressed gaseous hydrogen for heavy duty vehicle (HDV) refueling applications by refueling transit buses over a three-month period under real-world conditions. The system uses a submerged pump to deliver pressurized liquid H₂ from a cryogenic storage tank to a dispensing control loop that vaporizes the liquid and adjusts the pressure and temperature of the resulting gas to enable refueling at 35 MPa and temperatures as low as −40 °C, consistent with the SAE J2601 standard. Using our full-scale mobile refueler, we completed 118 individual bus filling events using 13 different vehicles, involving a total of 3,700 kg of H₂ dispensed. We report filling statistics from the entire campaign, details on individual fills (including fill times, final state of charge, benefits of pre-cooled fills, and back-to-back filling capabilities), and discuss transit agency feedback on technology performance. In our final test, the system successfully completed an endurance test using a single dispenser involving 52 consecutive individual fills over an 11.5-h period, dispensing 1,322 kg of H₂ with an average fill rate of 3.4 kg/min and peak rate of 7.1 kg/min, and reaching an average SOC of 97.6% across all fills.     

The design and optimization of a cryogenic compressed hydrogen refueling process

Cryo-compressed hydrogen storage has excellent volume and mass hydrogen storage density, which is the most likely way to meet the storage requirements proposed by United States Department of Energy（DOE）. This paper contributes to propose and analyze a new cryogenic compressed hydrogen refueling station. The new type of low temperature and high-pressure hydrogenation station system can effectively reduce the problems such as too high liquefaction work when using liquid hydrogen as the gas source, the need to heat and regenerate to release hydrogen, and the damage of thermal stress on the storage tank during the filling process, so as to reduce the release of hydrogen and ensure the non-destructive filling of hydrogen. This paper focuses on the study of precooling process in filling. By establishing a heat transfer model, the dynamic trend of tank temperature with time in the precooling process of low-temperature and high-pressure hydrogen storage tank under constant pressure is studied. Two analysis methods are used to provide theoretical basis for the selection of inlet diameter of hydrogen storage tank. Through comparative analysis of the advantages and disadvantages of the two analysis methods, it is concluded that the analysis method of constant mass flow is more suitable for the selection in practical applications. According to it, the recommended diameter of the storage tank at the initial temperature of 300 K, 200 K and 100 K is selected, which are all 15 mm. It is further proved that the calculation method can meet the different storage tank states of hydrogen fuel cell vehicles when selecting the pipe diameter.     

A thermodynamic analysis of refueling of a hydrogen tank

A thermodynamic analysis of refueling of a gaseous hydrogen fuel tank is described. This study may lend itself to the applications of refueling a hydrogen storage tank onboard a hydrogen fuel-cell vehicle. The gaseous hydrogen is treated as an ideal or a non-ideal gas. The refueling process is analyzed based on adiabatic, isothermal, or diathermal condition of the tank. A constant feed-rate is assumed in the analysis. The thermodynamic state of the feed stream also remains constant during refueling. Ideal-gas assumption results in simple closed-form expressions for tank temperature, pressure, and other parameters. The non-ideal behavior of high-pressure gaseous hydrogen is addressed using the newly developed equation of state for normal hydrogen, which is based on the reduced Helmholtz free energy formulation. Sample calculations are presented using initial tank and feed stream conditions commensurate to practical vehicular applications. Comparing to the non-ideal analysis, the ideal-gas assumption always results in under-prediction of the tank temperature and pressure irrespective of the filling condition. For a given target tank pressure, the refueling time is the shortest under adiabatic condition and is the longest under isothermal condition with the tank being maintained at the initial tank temperature. The adiabatic and isothermal conditions can be viewed, respectively, as the lower and upper bounds of the refueling time for a given final target tank pressure.     

Thermodynamic parametric analysis of refueling heavy-duty hydrogen fuel-cell electric vehicles

Reliable design and safe operation of heavy-duty hydrogen refueling stations are essential for the successful deployment of heavy-duty fuel cell electric vehicles (FCEVs). Fueling heavy-duty FCEVs is different from light-duty vehicles in terms of the dispensed hydrogen quantities and fueling rates, requiring tailored fueling station design for each vehicle class. In particular, the selection and design of the onboard hydrogen storage tank system and the fueling performance requirements influence the safe design of hydrogen fueling stations. A thermodynamic modeling and analysis are performed to evaluate the impact of various fueling parameters and boundary conditions on the fueling performance of heavy-duty FCEVs. We studied the effect of dispenser pressure ramp rate and precooling temperature, initial tank temperature and pressure, ambient temperature, and onboard storage design parameters, such as onboard storage pipe diameter and length, on the fueling rate and final vehicle state-of-charge, while observing prescribed tank pressure and temperature safety limits. An important finding was the sensitivity of the temporal fueling rate profile and the final tank state of charge to the design factors impacting pressure drop between the dispenser and vehicle tank, including onboard storage pipe diameter selection, and flow coefficients of nozzle, valves, and fittings. The fueling rate profile impacts the design and cost of the hydrogen precooling unit upstream of the dispenser.     

Thermodynamic modeling of hydrogen fueling process from high-pressure storage tank to vehicle tank

This study develops a hydrogen fueling station (HFS) thermodynamic model that simulates the actual fueling process in which hydrogen is supplied from a high-pressure (HP) storage tank into a fuel cell electric vehicle (FCEV) tank. To make the model as accurate as possible, we use the same components and specifications as in actual HFSs, such as a pressure control valve, a pre-cooling system, and an FCEV tank. After the components and their specifications are set, pressure and temperature profiles are set as the HP tank supply conditions. Based on the pressure and temperature profiles, the model solves for the temperature, pressure, and mass flow rate of hydrogen at each downstream position, including the inside of the vehicle tank. The values predicted by the model are compared with experimental data, and we show that the developed model makes it possible to accurately simulate those values at any position during the fueling process.     

Hydrogen refueling process from the buffer and the cascade storage banks to HV cylinder

The focus of this research is on refueling process from a buffer and a cascade storage bank. A thermodynamic analysis is developed to investigate the filling process of fuel transmission from a storage bank to hydrogen cylinder. Refueling Process from Buffer and Cascade Storage Banks is the subject of this research. Filling the hydrogen cylinder to the required final condition is influenced by the volume and pressure of storage bank. For both buffer and cascade storage banks, ambient temperature is also an important parameter that affects the initial condition, the final condition and the refueling process. Comparison of buffer and cascade storage banks showed that refueling time using buffer storage bank is 200 s less than the cascade storage bank. However, the energy required for gas storage is higher in buffer storage system. As shown by the study, reduction in the final temperature of the filling process can be achieved by controlling the ambient temperature, the initial pressure and the fuel charging rate.     

Neural network based optimization for cascade filling process of on-board hydrogen tank

Compressed hydrogen storage is widely used in hydrogen fuel cell vehicles (HFCVs). Cascade filling systems can provide different pressure levels associated with various source tanks allowing for a variable mass flow rate. To meet refueling performance objectives, safe and fast filling processes must be available to HFCVs. The main objective of this paper is to establish an optimization methodology to determine the initial thermodynamic conditions of the filling system that leads to the lowest final temperature of hydrogen in the on-board storage tank with minimal energy consumption. First, a zero-dimensional lumped parameter model is established. This simplified model, implemented in Matlab/Simulink, is then used to simulate the flow of hydrogen from cascade pressure tanks to an on-board hydrogen storage tank. A neural network is then trained with model calculation results and experimental data for multi-objective optimization. It is found to have good prediction, allowing the determination of optimal filling parameters. The study shows that a cascade filling system can well refuel the on-board storage tank with constant average pressure ramp rate (APRR). Furthermore, a strong pre-cooling system can effectively lower the final temperature at a cost of larger energy consumption. By using the proposed neural network, for charging times less than 183s, the optimization procedure predicts that the inlet temperature is 259.99–266.58 K, which can effectively reduce energy consumption by about 2.5%.     

Dynamic simulation for optimal hydrogen refueling method to Fuel Cell Vehicle tanks

A dynamic simulation approach to investigate an optimal hydrogen refueling method is proposed. The proposed approach simulates a transient temperature, pressure and mass flow rate of hydrogen flowing inside filling equipment in an actual station during the refueling process to an Fuel Cell Vehicle (FCV) tank. The simulation model is the same as in an actual hydrogen refueling station (HRS), and consists of a Break-Away, a hose, a nozzle, pipes and an FCV tank. Therefore, we can set actual configurations and thermal properties to the simulation model, and then simulate the temperature, pressure and mass flow rate of hydrogen passing through each position based on the supply conditions (temperature and pressure) at the Break-Away. In this study, the simulated temperature, pressure and mass flow rate are compared with the corresponding experimental data. Therefore, we show that the dynamic simulation approach can accurately obtain those values at each position during the refueling process and is an effective step in proposing the optimal refueling method.     

Developing an infrastructure for hydrogen vehicles: a Southern California case study

We have examined the technical feasibility and economics of developing a hydrogen vehicle refueling infrastructure for a specific area where zero emission vehicles are being considered, Southern California. Potential hydrogen demands for zero emission vehicles are estimated. We then assess in detail several near term possibilities for producing and delivering gaseous hydrogen transportation fuel including: (1) hydrogen produced from natural gas in a large, centralized steam reforming plant, and truck delivered as a liquid to refueling stations; (2) hydrogen produced in a large, centralized steam reforming plant, and delivered via small scale hydrogen gas pipeline to refueling stations; (3) by-product hydrogen from chemical industry sources; (4) hydrogen produced at the refueling station via small scale steam reforming of natural gas; and (5) hydrogen produced via small scale electrolysis at the refueling station. The capital cost of infrastructure and the delivered cost of hydrogen are estimated for each hydrogen supply option. Hydrogen is compared to other fuels for fuel cell vehicles (methanol, gasoline) in terms of vehicle cost, infrastructure cost and lifecycle cost of transportation. Finally, we discuss possible scenarios for introducing hydrogen as a fuel for fuel cell vehicles.     

CFD analysis of fast filling scenarios for 70 MPa hydrogen type IV tanks

High injection pressure is combined with high refueling rate for vehicles storing pressurized gaseous hydrogen onboard. As a drawback, high temperatures are developed inside the tank, which can jeopardize the structural integrity of the storage system. Computational Fluid Dynamics (CFD) codes already proved to be a valuable tool for predicting the temperature distribution within the tank during fast refueling. Results of hydrogen fast filling CFD simulations for a type IV tank, filled to 70 MPa at different working conditions are presented as follow up of the CFD model validation performed against experimental data. Alternative rates of pressure rise, adiabatic and cold filling are investigated to evaluate the effect on maximum hydrogen temperatures inside the tank. Results confirmed that the developed CFD model could be a suitable tool for investigating fast filling scenarios when experimental data are not yet available or of difficult realization.