China, People’s Republic
Investigation on the Effects of Blending Hydrogen-rich Gas in the Spark-ignition Engine
May 2022
Publication
In order to improve the energy efficiency of the internal combustion engine and replace fossil fuel with alternative fuels a concept of the methanol-syngas engine was proposed and the prototype was developed. Gasoline and dissociated methanol gas (GDM) were used as dual fuels and the engine performance was investigated by simulation and experiments. Dissociated methanol gas is produced by recycling the exhaust heat. The performance and combustion process was studied and compared with the gasoline engine counterpart. There is 1.9% energy efficiency improvement and 5.5% fuel consumption reduction under 2000r/min 100 N · m working condition with methanol substitution ratio of 10%. In addition the engine efficiency further improves with an increase of dissociated methanol gas substitution ratio because of the increased heating value of the fuel and effects of hydrogen. The peak pressure in the cylinder and the peak heat release rate of the GDM engine are higher than that of the original gasoline engine with a phase closer to the top dead center (TDC). Therefore blending hydrogen-rich gas in the spark-ignition engine can recycle the exhaust heat and improve the thermal efficiency of the engine.
An Ammonia-Hydrogen Energy Roadmap for Carbon Neutrality: Opportunity and Challenges in China
Nov 2021
Publication
China has promised to reach the peak carbon dioxide emission (ca. 10 billion tons) by 2030 and carbon neutrality by 2060. To realize these goals it is necessary to develop hydrogen energy and fuel cell techniques. However the high cost and low intrinsic safety of high-pressure hydrogen storage limit their commercialization. NH3 is high in hydrogen content easily liquefied at low pressure and free of carbon and the technology of NH3 synthesis has been commercialized nationwide. It is worth noting that the production of NH3 in China is about 56 million tons per year accounting for 35% of worldwide production. Hence with the well established infrastructure for NH3 synthesis and transportation and the demand for clean energy in China it is feasible to develop a green and economical energy roadmap viz. “Clean low-pressure NH3 synthesis → Safe and economical NH3 storage and transportation → Carbon-free efficient NH3-H2 utilization” for low-carbon or even carbon-free energy production.<br/>Currently the academic and industrial communities in China are striving to make technological breakthroughs in areas such as photocatalytic water splitting electrocatalytic water splitting mild-condition NH3 synthesis low-temperature NH3 catalytic decomposition and indirect or direct NH3 fuel cells with significant progress.<br/>Taking full advantage of the NH3 synthesis industry and readjusting the industrial structure it is viable to achieve energy saving and emission reduction in NH3 synthesis industry (440 million tons CO2 per year) as well as promote a new energy industry and ensure national energy security. Therefore relevant academic and industrial communities should put effort on mastering the key technologies of “Ammonia-Hydrogen” energy conversion and utilization with complete self-dependent intellectual property. It is envisioned that through the establishment of “Renewable Energy-Ammonia-Hydrogen” circular economy a green technology chain for hydrogen energy industry would pose as a promising pathway to achieve the 2030 and 2060 goals.
Simulation of Possible Fire and Explosion Hazards of Clean Fuel Vehicles in Garages
Nov 2021
Publication
Clean fuel is advocated to be used for sustainability. The number of liquefied petroleum gas (LPG) and hydrogen vehicles is increasing globally. Explosion hazard is a threat. On the other hand the use of hydrogen is under consideration in Hong Kong. Explosion hazards of these clean fuel (LPG and hydrogen) vehicles were studied and are compared in this paper. The computational fluid dynamics (CFD) software Flame Acceleration Simulator (FLACS) was used. A car garage with a rolling shutter as its entrance was selected for study. Dispersion of LPG from the leakage source with ignition at a higher position was studied. The same garage was used with a typical hydrogen vehicle leaking 3.4 pounds (1.5 kg) of hydrogen in 100 s the mass flow rate being equal to 0.015 kgs−1 . The hydrogen vehicle used in the simulation has two hydrogen tanks with a combined capacity of 5 kg. The entire tank would be completely vented out in about 333 s. Two scenarios of CFD simulation were carried out. In the first scenario the rolling shutter was completely closed and the leaked LPG or hydrogen was ignited at 300 s after leakage. The second scenario was conducted with a gap height of 0.3 m under the rolling shutter. Predicted results of explosion pressure and temperature show that appropriate active fire engineering systems are required when servicing these clean fuel vehicles in garages. An appropriate vent in an enclosed space such as the garage is important in reducing explosion hazards.
Investigation of Mixing Behavior of Hydrogen Blended to Natural Gas in Gas Network
Apr 2021
Publication
Hydrogen is of great significance for replacing fossil fuels and reducing carbon dioxide emissions. The application of hydrogen mixing with natural gas in gas network transportation not only improves the utilization rate of hydrogen energy but also reduces the cost of large-scale updating household or commercial appliance. This paper investigates the necessity of a gas mixing device for adding hydrogen to existing natural gas pipelines in the industrial gas network. A three-dimensional helical static mixer model is developed to simulate the mixing behavior of the gas mixture. In addition the model is validated with experimental results. Parametric studies are performed to investigate the effect of mixer on the mixing performance including the coefficient of variation (COV) and pressure loss. The research results show that based on the the optimum number of mixing units is three. The arrangement of the torsion angle of the mixing unit has a greater impact on the COV. When the torsion angle θ = 120◦ the COV has a minimum value of 0.66% and when the torsion angle θ = 60◦ the COV has a maximum value of 8.54%. The distance of the mixing unit has little effect on the pressure loss of the mixed gas but has a greater impact on the COV. Consecutive arrangement of the mixing units (Case A) is the best solution. Increasing the distance of the mixing unit is not effective for the gas mixing effect. Last but not least the gas mixer is optimized to improve the mixing performance.
Computational Intelligence Approach for Modeling Hydrogen Production: A Review
Mar 2018
Publication
Hydrogen is a clean energy source with a relatively low pollution footprint. However hydrogen does not exist in nature as a separate element but only in compound forms. Hydrogen is produced through a process that dissociates it from its compounds. Several methods are used for hydrogen production which first of all differ in the energy used in this process. Investigating the viability and exact applicability of a method in a specific context requires accurate knowledge of the parameters involved in the method and the interaction between these parameters. This can be done using top-down models relying on complex mathematically driven equations. However with the raise of computational intelligence (CI) and machine learning techniques researchers in hydrology have increasingly been using these methods for this complex task and report promising results. The contribution of this study is to investigate the state of the art CI methods employed in hydrogen production and to identify the CI method(s) that perform better in the prediction assessment and optimization tasks related to different types of Hydrogen production methods. The resulting analysis provides in-depth insight into the different hydrogen production methods modeling technique and the obtained results from various scenarios integrating them within the framework of a common discussion and evaluation paper. The identified methods were benchmarked by a qualitative analysis of the accuracy of CI in modeling hydrogen production providing extensive overview of its usage to empower renewable energy utilization.
Safety of Hydrogen Storage and Transportation: An Overview on Mechanisms, Techniques, and Challenges
Apr 2022
Publication
The extensive usage of fossil fuels has caused significant environmental pollution climate change and energy crises. The significant advantages of hydrogen such as cleanliness high efficiency and a wide range of sources make it quite promising. Hydrogen is prone to material damage which may lead to leakage. High-pressure leaking hydrogen is highly susceptible to spontaneous combustion due to its combustion characteristics which may cause jet fire or explosion accidents resulting in serious casualties and property damage. This paper presents a detailed review of the research progress on hydrogen leak diffusion characteristics leak spontaneous combustion mechanisms and material hydrogen damage mechanisms from the perspectives of theoretical analysis experiments and numerical simulations. This review points out that although a large number of research results have been obtained on the safety characteristics of hydrogen there are still some deficiencies and limitations. Further research topics are clarified such as further optimizing the kinetic mechanism of the high-pressure hydrogen leakage reaction and turbulence model exploring the expansion and dilution law of hydrogen clouds after liquid hydrogen flooding further studying the spontaneous combustion mechanism of leaked hydrogen and the interaction between mechanisms and investigating the synergistic damage effect of hydrogen and other components on materials. The leakage spontaneous combustion process in open space the development process of the bidirectional effect of hydrogen jet fuel and crack growth under the impact of high-pressure hydrogen jet fuel on the material may need to be explored next.
Flame Acceleration and Deflagration-to-Detonation Transition in Hydrogen-Oxygen Mixture in a Channel with Triangular Obstacles
Sep 2021
Publication
Study of flame acceleration and deflagration-to-detonation transition (DDT) in obstructed channels is an important subject of research for hydrogen safety. Experiments and numerical simulations of DDT in channels equipped with triangular obstacles were conducted in this work. High-speed schlieren photography and pressure records were used to study the flame shape changes flame propagation and pressure build up in the experiments. In the simulations the fully compressible reactive Navier–Stokes equations coupled with a calibrated chemical-diffusion model for stoichiometric hydrogen-oxygen mixture were solved using a high-order numerical method. The simulations were in good agreement with the experiments. The results show that the triangular obstacles significantly promote the flame acceleration and provide conditions for the occurrence of DDT. In the early stages of flame acceleration vortices are generated in the gaps between adjacent obstacles which is the main cause for the flame roll-up and distortion. A positive feedback mechanism between the combustiongenerated flow and flame propagation results in the variations of the size and velocity of vortices. The flame-vortex interactions cause flame fragmentation and consequently rapid growth in flame surface area which further lead to flame acceleration. The initially laminar flame then develops into a turbulent flame with the creation of shocks shock-flame interactions and various flame instabilities. The continuously arranged obstacles interact with shocks and flames and help to create environments in which a detonation can develop. Both flame collision and flame-shock interaction can give rise to detonation in the channels with triangular obstacles.
Hydrothermal Conversion of Lignin and Black Liquor for Phenolics with the Aids of Alkali and Hydrogen Donor
Jun 2019
Publication
The potentials of phenolic productions from lignin and black liquor (BL) via hydrothermal technology with the aids of alkalis and hydrogen donors were investigated by conducting batch experiments in micro-tube reactors with 300 °C sub-critical water as the solvent. The results showed that all the employed alkalis improved lignin degradation and thus phenolics production and the strong alkalis additionally manifested deoxygenation to produce more phenolics free of methoxyl group(s). Relatively hydrogen donors more visibly facilitated phenolics formation. Combination of strong alkali and hydrogen donors exhibited synergistically positive effects on producing phenolics (their total yield reaching 22 wt%) with high selectivities to phenolics among which the yields of catechol and cresols respectively peaked 16 and 3.5 wt%. BL could be hydrothermally converted into phenolics at high yields (approaching 10 wt% with the yields of catechol and cresols of about 4 and 2 wt% respectively) with the aids of its inherent alkali and hydrogen donors justifying its cascade utilization.
Transient Numerical Modeling and Model Predictive Control of an Industrial-scale Steam Methane Reforming Reactor
Mar 2021
Publication
A steam methane reforming reactor is a key equipment in hydrogen production and numerical analysis and process control can provide a critical insight into its reforming mechanisms and flexible operation in real engineering applications. The present paper firstly studies the transport phenomena in an industrial-scale steam methane reforming reactor by transient numerical simulations. Wall effect and local non thermal equilibrium is considered in the simulations. A temperature profile of the tube outer wall is given by user defined functions integrated into the ANSYS FLUENT software. Dynamic simulations show that the species distribution is closely related to the temperature distribution which makes the temperature of the reactor tube wall an important factor for the hydrogen production of the reformer and the thermal conductivity of the catalyst network is crucial in the heat transfer in the reactor. Besides there exists a delay of the reformer's hydrogen production when the temperature profile of the tube wall changes. Among inlet temperature inlet mass flow rate and inlet steam-to-carbon (S/C) ratio the mass flow rate is the most influencing factor for the hydrogen production. The dynamic matrix control (DMC) scheme is subsequently designed to manipulate the mole fraction of hydrogen of the outlet to the target value by setting the temperature profile trajectory of the reforming tube with time. The proportional-integral control strategy is also studied for comparison. The closed-loop simulation results show that the proposed DMC control strategy can reduce the overshoot and have a small change of the input variable. In addition the disturbances of feed disturbance can also be well rejected to assure the tracking performance indicating the superiority of the DMC controller. All the results give insight to the theoretical analysis and controller design of a steam methane reformer and demonstrate the potential of the CFD modeling in study the transport mechanism and the idea of combining CFD modelling with controller design for the real application.
Hydrogen Inhibition as Explosion Prevention in Wet Metal Dust Removal Systems
Mar 2022
Publication
Hydrogen energy attracts an amount of attention as an environmentally friendly and sustainable energy source. However hydrogen is also flammable. Hydrogen fires and explosions might occur in wet-dust-removal systems if accumulated aluminum dust reacts with water. Hydrogen inhibition is a safe method to address these issues. For this purpose we used sodium citrate a renewable and nontoxic raw material to inhibit H2 formation. Specifically hydrogen inhibition experiments with sodium citrate were carried out using custom-built equipment developed by our research group. When the concentration of sodium citrate solution was in the range of 0.4–4.0 g/L a protective coating was formed on the surface of the Al particles which prevented them from contacting with water. The inhibitory effect was achieved when the concentration of sodium citrate was in a certain range and too much or too little addition may reduce the inhibitory effect. In this paper we also discuss the economic aspects of H2 inhibition with this method because it offers excellent safety advantages and could be incorporated on a large scale. Such an intrinsic safety design of H2 inhibition to control explosions in wet-dust-removal systems could be applied to ensure the safety of other systems such as nuclear reactors.
An Improved Fuzzy PID Control Method Considering Hydrogen Fuel Cell Voltage-Output Characteristics for a Hydrogen Vehicle Power System
Sep 2021
Publication
The hydrogen fuel cell (HFC) vehicle is an important clean energy vehicle which has prospects for development. The behavior of the hydrogen fuel cell (HFC) vehicle power system and in particular the proton-exchange membrane fuel cell has been extensively studied as of recent. The development of the dynamic system modeling technology is of paramount importance for HFC vehicle studies; however it is hampered by the separation of the electrochemical properties and dynamic properties. In addition the established model matching the follow-up control method lacks applicability. In attempts to counter these obstructions we proposed an improved fuzzy (Proportional Integral Derivative) PID control method considering HFC voltage-output characteristics. By developing both the electrochemical and dynamic model for HFC vehicle we can realize the coordinated control of HFC and power cell. The simulation results are in good agreement with the experimental results in the two models. The proposed control algorithm has a good control effect in all stages of HFC vehicle operation.
Recent Progress on the Key Materials and Components for Proton Exchange Membrane Fuel Cells in Vehicle Applications
Jul 2016
Publication
Fuel cells are the most clean and efficient power source for vehicles. In particular proton exchange membrane fuel cells (PEMFCs) are the most promising candidate for automobile applications due to their rapid start-up and low-temperature operation. Through extensive global research efforts in the latest decade the performance of PEMFCs including energy efficiency volumetric and mass power density and low temperature startup ability have achieved significant breakthroughs. In 2014 fuel cell powered vehicles were introduced into the market by several prominent vehicle companies. However the low durability and high cost of PEMFC systems are still the main obstacles for large-scale industrialization of this technology. The key materials and components used in PEMFCs greatly affect their durability and cost. In this review the technical progress of key materials and components for PEMFCs has been summarized and critically discussed including topics such as the membrane catalyst layer gas diffusion layer and bipolar plate. The development of high-durability processing technologies is also introduced. Finally this review is concluded with personal perspectives on the future research directions of this area.
Hydrogen Production from the Air
Sep 2022
Publication
Green hydrogen produced by water splitting using renewable energy is the most promising energy carrier of the low-carbon economy. However the geographic mismatch between renewables distribution and freshwater availability poses a significant challenge to its production. Here we demonstrate a method of direct hydrogen production from the air namely in situ capture of freshwater from the atmosphere using hygroscopic electrolyte and electrolysis powered by solar or wind with a current density up to 574 mA cm−2 . A prototype of such has been established and operated for 12 consecutive days with a stable performance at a Faradaic efficiency around 95%. This so-called direct air electrolysis (DAE) module can work under a bone-dry environment with a relative humidity of 4% overcoming water supply issues and producing green hydrogen sustainably with minimal impact to the environment. The DAE modules can be easily scaled to provide hydrogen to remote (semi-) arid and scattered areas.
Safe Design of a Hydrogen-Powered Ship: CFD Simulation on Hydrogen Leakage in the Fuel Cell Room
Mar 2023
Publication
Adopting proton exchange membrane fuel cells fuelled by hydrogen presents a promising solution for the shipping industry’s deep decarbonisation. However the potential safety risks associated with hydrogen leakage pose a significant challenge to the development of hydrogen-powered ships. This study examines the safe design principles and leakage risks of the hydrogen gas supply system of China’s first newbuilt hydrogen-powered ship. This study utilises the computational fluid dynamics tool FLACS to analyse the hydrogen dispersion behaviour and concentration distributions in the hydrogen fuel cell room based on the ship’s parameters. This study predicts the flammable gas cloud and time points when gas monitoring points first reach the hydrogen volume concentrations of 0.8% and 1.6% in various leakage scenarios including four different diameters (1 3 5 and 10 mm) and five different directions. This study’s findings indicate that smaller hydrogen pipeline diameters contribute to increased hydrogen safety. Specifically in the hydrogen fuel cell room a single-point leakage in a hydrogen pipeline with an inner diameter not exceeding 3 mm eliminates the possibility of flammable gas cloud explosions. Following a 10 mm leakage diameter the hydrogen concentration in nearly all room positions reaches 4.0% within 6 s of leakage. While the leakage diameter does not impact the location of the monitoring point that first activates the hydrogen leak alarm and triggers an emergency hydrogen supply shutdown the presence of obstructions near hydrogen detectors and the leakage direction can affect it. These insights provide guidance on the optimal locations for hydrogen detectors in the fuel cell room and the pipeline diameters on hydrogen gas supply systems which can facilitate the safe design of hydrogen-powered ships.
New Liquid Chemical Hydrogen Storage Technology
Aug 2022
Publication
The liquid chemical hydrogen storage technology has great potentials for high-density hydrogen storage and transportation at ambient temperature and pressure. However its commercial applications highly rely on the high-performance heterogeneous dehydrogenation catalysts owing to the dehydrogenation difficulty of chemical hydrogen storage materials. In recent years the chemists and materials scientists found that the supported metal nanoparticles (MNPs) can exhibit high catalytic activity selectivity and stability for the dehydrogenation of chemical hydrogen storage materials which will clear the way for the commercial application of liquid chemical hydrogen storage technology. This review has summarized the recent important research progress in the MNP-catalyzed liquid chemical hydrogen storage technology including formic acid dehydrogenation hydrazine hydrate dehydrogenation and ammonia borane dehydrogenation discussed the urgent challenges in the key field and pointed out the future research trends.
Cow Dung Gasification Process for Hydrogen Production Using Water Vapor as Gasification Agent
Jun 2022
Publication
In recent years with the development of hydrogen energy economy there is an increasing demand for hydrogen in the market and hydrogen production through biomass will provide an important way to supply clean environmentally friendly and highly efficient hydrogen. In this study cow dung was selected as the biomass source and the efficiency of the biomass to hydrogen reaction was explored by coupling high temperature pyrolysis and water vapor gasification. The experimental conditions of gasification temperature water mass fraction heating rate and feed temperature were systematically studied and optimized to determine the optimal conditions for in situ hydrogen production by gasification of cow dung. The relationship of each factor to the yield of hydrogen production by gasification of cow dung semi-coke was investigated in order to elucidate the mechanism of the hydrogen production. The experiment determined the optimal operating parameters of in situ gasification: gasification temperature 1173 K water mass fraction 80% heating rate 10 K/min and feed temperature 673 K. The semi-coke treatment separated high temperature pyrolysis and water vapor gasification and reduced the influence on gasification of volatile substances such as tar extracted from pyrolysis. The increase of semi-coke preparation temperature increases the content of coke reduces the volatile matter and improves the yield of hydrogen; the small size of semi-coke particles and large specific surface area are beneficial to the gasification reaction.
Numerical Simulation on Hydrogen Leakage and Dispersion Behavior in Hydrogen Energy Infrastructures
Sep 2021
Publication
Unexpected hydrogen leakage may occur in the production storage transportation and utilization of hydrogen. The lower flammability limit (LFL) for the hydrogen is 4% in air. The combustion and explosion of hydrogen-air mixture poses potential hazards to personnel and property. In this study unintended release of hydrogen from a hydrogen fuel cell forklift vehicle inside a enclosed warehouse is simulated by fireFoam which is an LES Navier-Stokes CFD solver. The simulation results are verified by experimental data. The variation of hydrogen concentration with time and the isosurface of hydrogen concentration of 4% vol. are given. Furthermore the leakage of hydrogen from a storage tanks in a hydrogen refueling station is simulated and the evolution of the isosurface of hydrogen concentration of 4% vol. is given which provides a quantitative guidence for determination the hazardous area after the leakage of hydrogen.
Analysis of Crash Characteristics of Hydrogen Storage Structure of Hydrogen Powered UAV
Nov 2022
Publication
In the context of green aviation as an internationally recognized solution hydrogen energy is lauded as the “ultimate energy source of the 21st century” with zero emissions at the source. Developed economies with aviation industries such as Europe and the United States have announced hydrogen energy aviation development plans successively. The study and development of high-energy hydrogen fuel cells and hydrogen energy power systems have become some of the future aviation research focal points. As a crucial component of hydrogen energy storage and delivery the design and development of a safe lightweight and efficient hydrogen storage structure have drawn increasing consideration. Using a hydrogen-powered Unmanned Aerial Vehicle (UAV) as the subject of this article the crash characteristics of the UAV’s hydrogen storage structure are investigated in detail. The main research findings are summarized as follows: (1) A series of crash characteristics analyses of the hydrogen storage structure of a hydrogen-powered UAV were conducted and the Finite Element Analysis (FEA) response of the structure under different impact angles internal pressures and impact speeds was obtained and analyzed. (2) When the deformation of the hydrogen storage structure exceeds 50 mm and the strain exceeds 0.8 an initial crack will appear at this part of the hydrogen storage structure. The emergency release valve should respond immediately to release the gas inside the tank to avoid further damage. (3) Impact angle and initial internal pressure are the main factors affecting the formation of initial cracks.
Influence of Hydrogen Production in the CO2 Emissions Reduction of Hydrogen Mettalurgy Transformation in Iron and Steel Industry
Jan 2023
Publication
The transformation of hydrogen metallurgy is a principal means of promoting the iron and steel industry (ISI) in reaching peak and deep emissions reduction. However the environmental impact of different hydrogen production paths on hydrogen metallurgy has not been systemically discussed. To address this gap based on Long-range Energy Alternatives Planning System (LEAP) this paper constructs a bottom-up energy system model that includes hydrogen production iron and steel (IS) production and power generation. By setting three hydrogen production structure development paths namely the baseline scenario business-as-usual (BAU) scenario and clean power (CP) scenario the carbon dioxide (CO2) emissions impact of different hydrogen production paths on hydrogen metallurgy is carefully evaluated from the perspective of the whole industry and each IS production process. The results show that under the baseline scenario the hydrogen metallurgy transition will help the CO2 emissions of ISI peak at 2.19 billion tons in 2024 compared to 2.08 billion tons in 2020 and then gradually decrease to 0.78 billion tons in 2050. However different hydrogen production paths will contribute to the reduction or inhibit the reduction. In 2050 the development of electrolysis hydrogen production with renewable electricity will reduce CO2 emissions by an additional 48.76 million tons (under the CP scenario) while the hydrogen production mainly based on coal gasification and methane reforming will increase the additional 50.04 million tons CO2 emissions (under the BAU scenario). Moreover under the hydrogen production structure relying mainly on fossil and industrial by-products the technological transformation of blast furnace ironmaking with hydrogen injections will leak carbon emissions to the upstream energy processing and conversion process. Furthermore except for the 100% scrap based electric arc furnace (EAF) process the IS production process on hydrogen-rich shaft furnace direct reduced iron (hydrogen-rich DRI) have lower CO2 emissions than other processes. Therefore developing hydrogen-rich DRI will help the EAF steelmaking development to efficiently reduce CO2 emissions under scrap constraints.
Review on the Hydrogen Dispersion and the Burning Behavior of Fuel Cell Electric Vehicles
Oct 2022
Publication
The development of a hydrogen energy-based society is becoming the solution for more and more countries. Fuel cell electric vehicles are the best carriers for developing a hydrogen energy-based society. The current research on hydrogen leakage and the diffusion of fuel cell electric vehicles has been sufficient. However the study of hydrogen safety has not reduced the safety concerns for society and government management departments concerning the large-scale promotion of fuel cell electric vehicles. Hydrogen safety is both a technical and psychological issue. This paper aims to provide a comprehensive overview of fuel cell electric vehicles’ hydrogen dispersion and the burning behavior and introduce the relevant work of international standardization and global technical regulations. The CFD simulations in tunnels underground car parks and multistory car parks show that the hydrogen escape performance is excellent. At the same time the research verifies that the flow the direction of leakage and the vehicle itself are the most critical factors affecting hydrogen distribution. The impact of the leakage location and leakage pore size is much smaller. The relevant studies also show that the risk is still controllable even if the hydrogen leakage rate is increased ten times the limit of GTR 13 to 1000 NL/min and then ignited. Multi-vehicle combustion tests of fuel cell electric vehicles showed that adjacent vehicles were not ignited by the hydrogen. This shows that as long as the appropriate measures are taken the risk of a hydrogen leak or the combustion of fuel cell electric vehicles is controllable. The introduction of relevant standards and regulations also indirectly proves this point. This paper will provide product design guidelines for R&D personnel offer the latest knowledge and guidance to the regulatory agencies and increase the public’s acceptance of fuel cell electric vehicles.
Numerical Study on Protective Measures for a Skid-Mounted Hydrogen Refueling Station
Jan 2023
Publication
Hydrogen refueling stations are one of the key infrastructure components for the hydrogen-fueled economy. Skid-mounted hydrogen refueling stations (SHRSs) can be more easily commercialized due to their smaller footprints and lower costs compared to stationary hydrogen refueling stations. The present work modeled hydrogen explosions in a skid-mounted hydrogen refueling station to predict the overpressures for hydrogen-air mixtures and investigate the protective effects for different explosion vent layouts and protective wall distances. The results show that the explosive vents with the same vent area have similar overpressure reduction effects. The layout of the explosion vent affects the flame shape. Explosion venting can effectively reduce the inside maximum overpressure by 61.8%. The protective walls can reduce the overpressures but the protective walls should not be too close to the SHRS because high overpressures are generated inside the walls due to the confined shock waves. The protective wall with a distance of 6 m can effectively protect the surrounding people and avoid the secondary overpressure damage to the container.
Hydrogen Leakage Simulation and Risk Analysis of Hydrogen Fueling Station in China
Sep 2022
Publication
Hydrogen is a renewable energy source with various features clean carbon-free high energy density which is being recognized internationally as a “future energy.” The US the EU Japan South Korea China and other countries or regions are gradually clarifying the development position of hydrogen. The rapid development of the hydrogen energy industry requires more hydrogenation infrastructure to meet the hydrogenation need of hydrogen fuel cell vehicles. Nevertheless due to the frequent occurrence of hydrogen infrastructure accidents their safety has become an obstacle to large-scale construction. This paper analyzed five sizes (diameters of 0.068 mm 0.215 mm 0.68 mm 2.15 mm and 6.8 mm) of hydrogen leakage in the hydrogen fueling station using Quantitative Risk Assessment (QRA) and HyRAM software. The results show that unignited leaks occur most frequently; leaks caused by flanges valves instruments compressors and filters occur more frequently; and the risk indicator of thermal radiation accident and structure collapse accident caused by over-pressure exceeds the Chinese individual acceptable risk standard and the risk indicator of a thermal radiation accident and head impact accident caused by overpressure is below the Chinese standard. On the other hand we simulated the consequences of hydrogen leak from the 45 MPa hydrogen storage vessels by the physic module of HyRAM and obtained the ranges of plume dispersion jet fire radiative heat flux and unconfined overpressure. We suggest targeted preventive measures and safety distance to provide references for hydrogen fueling stations’ safe construction and operation.
A Real-Time Load Prediction Control for Fuel Cell Hybrid Vehicle
May 2022
Publication
The development of hydrogen energy is an effective solution to the energy and environmental crisis. Hydrogen fuel cells and energy storage cells as hybrid power have broad application prospects in the field of vehicle power. Energy management strategies are key technologies for fuel cell hybrid systems. The traditional optimization strategy is generally based on optimization under the global operating conditions. The purpose of this project is to develop a power allocation optimization method based on real-time load forecasting for fuel cell/lithium battery hybrid electric vehicles which does not depend on specific working conditions or causal control methods. This paper presents an energy-management algorithm based on real-time load forecasting using GRU neural networks to predict load requirements in the short time domain and then the local optimization problem for each predictive domain is solved using a method based on Pontryagin’s minimum principle (PMP). The algorithm adopts the idea of model prediction control (MPC) to transform the global optimization problem into a series of local optimization problems. The simulation results show that the proposed strategy can achieve a good fuel-saving control effect. Compared with the rule-based strategy and equivalent hydrogen consumption strategy (ECMS) the fuel consumption is lower under two typical urban conditions. In the 1800 s driving cycle under WTCL conditions the fuel consumption under the MPC-PMP strategy is 22.4% lower than that based on the ECMS strategy and 10.3% lower than the rules-based strategy. Under CTLT conditions the fuel consumption of the MPC-PMP strategy is 13.12% lower than that of the rule-based strategy and 3.01% lower than the ECMS strategy.
Roadmap to Hybrid Offshore System with Hydrogen and Power Co-generation
Sep 2021
Publication
Constrained by the expansion of the power grid the development of offshore wind farms may be hindered and begin to experience severe curtailment or restriction. The combination of hydrogen production through electrolysis and hydrogen-to-power is considered to be a potential option to achieve the goal of low-carbon and energy security. This work investigates the competitiveness of different system configurations to export hydrogen and/or electricity from offshore plants with particular emphasis on unloading the mixture of hydrogen and electricity to end-users on land. Including the levelized energy cost and net present value a comprehensive techno-economic assessment method is proposed to analyze the offshore system for five scenarios. Assuming that the baseline distance is 10 km the results show that exporting hydrogen to land through pipelines shows the best economic performance with the levelized energy cost of 3.40 $/kg. For every 10 km increase in offshore distance the net present value of the project will be reduced by 5.69 MU$ and the project benefit will be positive only when the offshore distance is less than 53.5 km. An important finding is that the hybrid system under ship transportation mode is not greatly affected by the offshore distance. Every 10% increase in the proportion of hydrogen in the range of 70%–100% can increase the net present value by 1.43–1.70 MU$ which will increase by 7.36–7.37 MU$ under pipeline transportation mode. Finally a sensitivity analysis was carried out to analyze the wind speed electricity and hydrogen prices on the economic performance of these systems.
Thermodynamics and Kinetics of Hydriding and Dehydriding Reactions in Mg-based Hydrogen Storage Materials
Oct 2021
Publication
Mg-based materials are one of the most promising hydrogen storage candidates due to their high hydrogen storage capacity environmental benignity and high Clarke number characteristics. However the limited thermodynamics and kinetic properties pose major challenges for their engineering applications. Herein we review the recent progress in improving their thermodynamics and kinetics with an emphasis on the models and the influence of various parameters in the calculated models. Subsequently the impact of alloying composite and nano-crystallization on both thermodynamics and dynamics are discussed in detail. In particular the correlation between various modification strategies and the hydrogen capacity dehydrogenation enthalpy and temperature hydriding/dehydriding rates are summarized. In addition the mechanism of hydrogen storage processes of Mg-based materials is discussed from the aspect of classical kinetic theories and microscope hydrogen transferring behavior. This review concludes with an outlook on the remaining challenge issues and prospects.
Influence of Hydrogen Environment on Fatigue Fracture Morphology of X80 Pipeline Steel
Dec 2022
Publication
The rapid development of hydrogen energy requires the use of natural gas infrastructure for hydrogen transportation. It is very important to study hydrogen-added natural gas transportation technology which is a key way to rapidly develop coal-based gas and renewable energy. This study aims to study the influence of X80 pipeline steel's fatigue performance in hydrogen environment and perform fatigue tests on notched round rod specimens under different hydrogen concentration. The experimental results show that hydrogen seriously affects the fatigue life of pipeline steel. After reaching a certain hydrogen concentration as the hydrogen concentration continues to increase the fatigue life decreases gradually. Combined with SEM analysis of fracture morphology the decrease in the size and density of the dimples reduces the displacement amplitude while the increase in the planar area increases the displacement during fatigue fracture due to accelerated crack propagation. From this study we can know the influence of hydrogen concentration on the fracture morphology of pipeline steel which provides an understanding of the effect of hydrogen on fatigue fracture morphology and a broader safety analysis.
Scenario-Based Comparative Analysis for Coupling Electricity and Hydrogen Storage in Clean Oilfield Energy Supply System
Mar 2022
Publication
In response to the objective of fully attaining carbon neutrality by 2060 people from all walks of life are pursuing low-carbon transformation. Due to the high water cut in the middle and late phases of development the oilfield’s energy consumption will be quite high and the rise in energy consumption will lead to an increase in carbon emission at the same time. As a result the traditional energy model is incapable of meeting the energy consumption requirement of high water cut oilfields in their middle and later phases of development. The present wind hydrogen coupling energy system was researched and coupled with the classic dispersed oilfield energy system to produce energy for the oilfields in this study. This study compares four future energy system models to existing ones computes the energy cost and net present value of an oilfield in Northwest China and proposes a set of economic evaluation tools for oilfield energy systems. The study’s findings indicate that scenario four provides the most economic and environmental benefits. This scenario effectively addresses the issue of high energy consumption associated with aging oilfields at this point significantly reduces carbon emissions absorbs renewable energy locally and reduces the burden on the power grid system. Finally sensitivity analysis is utilized to determine the effect of wind speed electricity cost and oilfield gas output on the system’s economic performance. The results indicate that the system developed in this study can be applied to other oilfields.
Sustainable Offshore Oil and Gas Fields Development: Techno-economic Feasibility Analysis of Wind–hydrogen–natural Gas Nexus
Jul 2021
Publication
Offshore oil and gas field development consumes quantities of electricity which is usually provided by gas turbines. In order to alleviate the emission reduction pressure and the increasing pressure of energy saving governments of the world have been promoting the reform of oil and gas fields for years. Nowadays environmentally friendly alternatives to provide electricity are hotspots such as the integration of traditional energy and renewable energy. However the determination of system with great environmental and economic benefits is still controversial. This paper proposed a wind– hydrogen–natural gas nexus (WHNGN) system for sustainable offshore oil and gas fields development. Combining the optimization model with the techno-economic evaluation model a comprehensive evaluation framework is established for techno-economic feasibility analysis. In addition to WHNGN system another two systems are designed for comparison including the traditional energy supply (TES) system and wind–natural gas nexus (WNGN) system. An offshore production platforms in Bohai Bay in China is taken as a case and the results indicate that: (i) WNGN and WHNGN systems have significant economic benefits total investment is decreased by 5190 and 5020 million $ respectively and the WHNGN system increases 4174 million $ profit; (ii) WNGN and WHNGN systems have significant environmental benefits annual carbon emission is decreased by 15 and 40.2 million kg respectively; (iii) the system can be ranked by economic benefits as follows: WHNGN >WNGN > TES; and (iV) the WHNGN system is more advantageous in areas with high hydrogen and natural gas sales prices such as China Kazakhstan Turkey India Malaysia and Indonesia.
Research on Hydrogen Consumption and Driving Range of Hydrogen Fuel Cell Vehicle under the CLTC-P Condition
Dec 2021
Publication
Hydrogen consumption and mileage are important economic indicators of fuel cell vehicles. Hydrogen consumption is the fundamental reason that restricts mileage. Since there are few quantitative studies on hydrogen consumption during actual vehicle operation the high cost of hydrogen consumption in outdoor testing makes it impossible to guarantee the accuracy of the test. Therefore this study puts forward a test method based on the hydrogen consumption of fuel cell vehicles under CLTC-P operating conditions to test the hydrogen consumption of fuel cell vehicles per 100 km. Finally the experiment shows that the mileage calculated by hydrogen consumption has a higher consistency with the actual mileage. Based on this hydrogen consumption test method the hydrogen consumption can be accurately measured and the test time and cost can be effectively reduced.
An Effective Optimisation Method for Coupled Wind–Hydrogen Power Generation Systems Considering Scalability
Jan 2023
Publication
A wind–hydrogen coupled power generation system can effectively reduce the power loss caused by wind power curtailment and further improve the ability of the energy system to accommodate renewable energy. However the feasibility and economy of deploying such a power generation system have not been validated through large‐scale practical applications and the economic comparison between regions and recommendations on construction are still lacking. In order to solve the aforementioned problems this paper establishes an economic analysis model for the wind–hydrogen coupled power generation system and proposes a linear optimisation‐based priority analysis method focusing on the major net present value for regional energy system as well as a cost priority analysis method for hydrogen production within sample power plants. The case study proves the effectiveness of the proposed analysis methods and the potential to develop wind–hydrogen coupled power generation systems in various provinces is compared based on the national wind power data in recent years. This provides recommendations for the future pilot construction and promotion of wind–hydrogen coupled power generation systems in China.
Effect of Hydrogen-blended Natural Gas on Combustion Stability and Emission of Water Heater Burner
Jun 2022
Publication
To study the effect of hydrogen-blended natural gas on the combustion stability and emission of domestic gas water heater a test system is built in this paper taking a unit of the partial premixed burner commonly used in water heaters as the object. Under the heat load of 0.7~2.3kW the changes of flame shape burner temperature and pollutant emission of natural gas with hydrogen volume ratio of 0~40% are studied with independent control of primary air supply and mixing. The results show that: with the increase of hydrogen blending ratio the inner flame height increases firstly and then reduces while the change of burner temperature is opposite. The maximum inner flame height and the minimum temperature of the burner both appear at the hydrogen blending ratio of 10~20%. It can be seen that the limit of hydrogen blending ratio which can maintain the burner operate safely and stably under rated heat load is 40% through the maximum temperature distribution on the burner surface. The CO emission in the flue gas gradually decreases with the increase of hydrogen blending ratio while the NOx emission fluctuates slightly when the hydrogen blending ratio is less than 20% but then decreases gradually.
A Review on Numerical Simulation of Hydrogen Production from Ammonia Decomposition
Jan 2023
Publication
Ammonia (NH3 ) is regarded as a promising medium of hydrogen storage due to its large hydrogen storage density decent performance on safety and moderate storage conditions. On the user side NH3 is generally required to decompose into hydrogen for utilization in fuel cells and therefore it is vital for the NH3 -based hydrogen storage technology development to study NH3 decomposition processes and improve the decomposition efficiency. Numerical simulation has become a powerful tool for analyzing the NH3 decomposition processes since it can provide a revealing insight into the heat and mass transfer phenomena and substantial guidance on further improving the decomposition efficiency. This paper reviews the numerical simulations of NH3 decomposition in various application scenarios including NH3 decomposition in microreactors coupled combustion chemical reactors solid oxide fuel cells and membrane reactors. The models of NH3 decomposition reactions in various scenarios and the heat and mass transport in the reactor are elaborated. The effects of reactor structure and operating conditions on the performance of NH3 decomposition reactor are analyzed. It can be found that NH3 decomposition in microchannel reactors is not limited by heat and mass transfer and NH3 conversion can be improved by using membrane reactors under the same conditions. Finally research prospects and opportunities are proposed in terms of model development and reactor performance improvement for NH3 decomposition.
Exergy and Exergoeconomic Analysis for the Proton Exchange Membrane Water Electrolysis under Various Operating Conditions and Design Parameters
Nov 2022
Publication
Integrating the exergy and economic analyses of water electrolyzers is the pivotal way to comprehend the interplay of system costs and improve system performance. For this a 3D numerical model based on COMSOL Multiphysics Software (version 5.6 COMSOL Stockholm Sweden) is integrated with the exergy and exergoeconomic analysis to evaluate the exergoeconomic performance of the proton exchange membrane water electrolysis (PEMWE) under different operating conditions (operating temperature cathode pressure current density) and design parameter (membrane thickness). Further the gas crossover phenomenon is investigated to estimate the impact of gas leakage on analysis reliability under various conditions and criteria. The results reveal that increasing the operating temperature or decreasing the membrane thickness improves both the efficiency and cost of hydrogen exergy while increasing the gas leakage through the membrane. Likewise raising the current density and the cathode pressure lowers the hydrogen exergy cost and improves the economic performance. The increase in exergy destroyed and hydrogen exergy cost as well as the decline in second law efficiency due to the gas crossover are more noticeable at higher pressures. As the cathode pressure rises from 1 to 30 bar at a current density of 10000 A/m2 the increase in exergy destroyed and hydrogen exergy cost as well as the decline in second law efficiency are increased by 37.6 kJ/mol 4.49 USD/GJ and 7.1% respectively. The cheapest green electricity source which is achieved using onshore wind energy and hydropower reduces hydrogen production costs and enhances economic efficiency. The growth in the hydrogen exergy cost is by about 4.23 USD/GJ for a 0.01 USD/kWh increase in electricity price at the current density of 20000 A/m2. All findings would be expected to be quite useful for researchers engaged in the design development and optimization of PEMWE.
A Review of Key Components of Hydrogen Recirculation Subsystem for Fuel Cell Vehicles
Jul 2022
Publication
Hydrogen energy and fuel cell technology are critical clean energy roads to pursue carbon neutrality. The proton exchange membrane fuel cell (PEMFC) has a wide range of commercial application prospects due to its simple structure easy portability and quick start-up. However the cost and durability of the PEMFC system are the main barriers to commercial applications of fuel cell vehicles. In this paper the core hydrogen recirculation components of fuel cell vehicles including mechanical hydrogen pumps ejectors and gas–water separators are reviewed in order to understand the problems and challenges in the simulation design and application of these components. The types and working characteristics of mechanical pumps used in PEMFC systems are summarized. Furthermore corresponding design suggestions are given based on the analysis of the design challenges of the mechanical hydrogen pump. The research on structural design and optimization of ejectors for adapting wide power ranges of PEMFC systems is analyzed. The design principle and difficulty of the gas–water separator are summarized and its application in the system is discussed. In final the integration and control of hydrogen recirculation components controlled cooperatively to ensure the stable pressure and hydrogen supply of the fuel cell under dynamic loads are reviewed.
Experimental Study on Flame Characteristics of Cryogenic Hydrogen Jet Fire
Sep 2021
Publication
In this work cryogenic hydrogen fires at fixed pressures and various initial temperatures were investigated experimentally. Flame length width heat fluxes and temperatures in down-stream regions were measured for the scenarios with 1.6-3 mm jet nozzle 106 to 273 K 2-5 barabs. The results show that the flame size is related to not only the jet nozzle diameter but also the release pressure and initial temperature. The correlations of normalized flame length and width are proposed with the stagnation pressure and the ratio of ambient and stagnation temperatures. Under constant pressure the flame size total radiative power and radiation fraction increase with the decrease of temperature due to lower choked flow velocity and higher density of cryogenic hydrogen. The correlation of radiation fraction proposed by Molina et al. at room temperature is not suitable to predict the cryogenic hydrogen jet fires. Based on piecewise polynomial law
Progress and Prospects of Hydrogen Production: Opportunities and challenges
Jan 2021
Publication
This study presents an overview of the current status of hydrogen production in relation to the global requirement for energy and resources. Subsequently it symmetrically outlines the advantages and disadvantages of various production routes including fossil fuel/biomass conversion water electrolysis microbial fermentation and photocatalysis (PC) in terms of their technologies economy energy consumption and costs. Considering the characteristics of hydrogen energy and the current infrastructure issues it highlights that onsite production is indispensable and convenient for some special occasions. Finally it briefly summarizes the current industrialization situation and presents future development and research directions such as theoretical research strengthening renewable raw material development process coupling and sustainable energy use.
Investigation on the Changes of Pressure and Temperature in High Pressure Filling of Hydrogen Storage Tank
May 2022
Publication
Hydrogen as fuel has been considered as a feasible energy carry and which offers a clean and efficient alternative for transportation. During the high pressure filling the temperature in the hydrogen storage tank (HST) may rise rapidly due to the hydrogen compression. The high temperature may lead to safety problem. Thus for fast and safely refueling the hydrogen several key factors need to be considered. In the present study by the thermodynamics theories a mathematical model is established to simulate and analyze the high pressure filling process of the storage tank for the hydrogen station. In the analysis the physical parameters of normal hydrogen are introduced to make the simulation close to the actual process. By the numerical simulation for 50 MPa compressed hydrogen tank the temperature and pressure trends during filling are obtained. The simulation results for non-adiabatic filling were compared with the theoretically calculated ones for adiabatic conditions and the simulation results for non-adiabatic filling were compared with the simulation ones for adiabatic conditions. Then the influence of working pressure initial temperature mass flow rate initial pressure and inlet temperature on the temperature rise were analyzed. This study provides a theoretical research basis for high pressure hydrogen energy storage and hydrogenation technology.
Numerical Modeling for Rapid Charging of Hydrogen Gas Vessel in Fuel Cell Vehicle
Feb 2023
Publication
As a fuel for power generation high-pressure hydrogen gas is widely used for transportation and its efficient storage promotes the development of fuel cell vehicles (FCVs). However as the filling process takes such a short time the maximum temperature in the storage tank usually undergoes a rapid increase which has become a thorny problem and poses great technical challenges to the steady operation of hydrogen FCVs. For security reasons SAE J2601/ISO 15869 regulates a maximum temperature limit of 85 ◦C in the specifications for refillable hydrogen tanks. In this paper a two-dimensional axisymmetric and a three-dimensional numerical model for fast charging of Type III 35 MPa and 70 MPa hydrogen vehicle cylinders are proposed in order to effectively evaluate the temperature rise within vehicle tanks. A modified standard k-ε turbulence model is utilized to simulate hydrogen gas charging. The equation of state for hydrogen gas is adopted with the thermodynamic properties taken from the National Institute of Standards and Technology (NIST) database taking into account the impact of hydrogen gas’ compressibility. To validate the numerical model three groups of hydrogen rapid refueling experimental data are chosen. After a detailed comparison it is found that the simulated results calculated by the developed numerical model are in good agreement with the experimental results with average temperature differences at the end time of 2.56 K 4.08 K and 4.3 K. The present study provides a foundation for in-depth investigations on the structural mechanics analysis of hydrogen gas vessels during fast refueling and may supply some technical guidance on the design of charging experiments.
Computational Investigation of Combustion, Performance, and Emissions of a Diesel-Hydrogen Dual-Fuel Engine
Feb 2023
Publication
This paper aims to expose the effect of hydrogen on the combustion performance and emissions of a high-speed diesel engine. For this purpose a three-dimensional dynamic simulation model was developed using a reasonable turbulence model and a simplified reaction kinetic mechanism was chosen based on experimental data. The results show that in the hydrogen enrichment conditions hydrogen causes complete combustion of diesel fuel and results in a 17.7% increase in work capacity. However the increase in combustion temperature resulted in higher NOx emissions. In the hydrogen substitution condition the combustion phases are significantly earlier with the increased hydrogen substitution ratio () which is not conducive to power output. However when the is 30% the CO soot and THC reach near-zero emissions. The effect of the injection timing is also studied at an HSR of 90%. When delayed by 10° IMEP improves by 3.4% compared with diesel mode and 2.4% compared with dual-fuel mode. The NOx is reduced by 53% compared with the original dual-fuel mode. This study provides theoretical guidance for the application of hydrogen in rail transportation.
Oxygen Carriers for Chemical-looping Water Splitting to Hydrogen Production: A Critical Review
Oct 2021
Publication
Chemical looping water splitting (CLWS) process using metal oxides or perovskites as oxygen carriers (OCs) is capable of producing pure H2 in an efficient simple and flexible way. The OCs are first reduced by hydrocarbon fuels and then oxidized by steam in a cyclic way. After the condensation of the gaseous mixture of steam and H2 from the oxidation step pure H2 is obtained. In recent years great efforts for CLWS have been made to improve the redox activity and stability of OCs. In this paper the development of the OCs for hydrogen production from CLWS were discussed. Effects of supports and additives on the performances of OCs were compared based on redox reactions in CLWS. Fe-based OCs with CeO2 Al2O3 ZrO2 CuO MoO3 Rh etc. are very attractive for the CLWS process. Issues and challenges for the development of OCs were analyzed.
Experiment and Numerical Study of the Combustion Behavior of Hydrogen-blended Natural Gas in Swirl Burners
Oct 2022
Publication
Hydrogen production from renewable energy is gaining increasing attention to enhance energy consumption structure and foster a more eco-friendly and sustainable society. At the same time mixing hydrogen with natural gas and supplying it to civilians is one of the best ways to reduce carbon emissions and increase the reliability of technology while reducing the costs of storing and transporting hydrogen. Even though numerous researchers have conducted experimental and simulation studies on hydrogen-doped natural gas most of these studies have focused on the effects of hydrogen-doped ratio equivalence ratio and fuel combustion mode. The impact of burner structure on hydrogen-enriched natural gas has not received much attention. Compared with conventional direct-flow combustion swirl combustion can improve the mixing effect of the fuel mixture during combustion and the use of regions of reversed flow due to swirl can make the fuel burn more fully to achieve the reduction of pollutant emissions. Swirling flames are widely used in gas turbines and industrial furnaces because of their high stability. However the application of swirl combustion in domestic equipment is still in its infancy which deserves more researchers to explore and enhance the working conditions of domestic combustion equipment. In this paper a three-dimensional swirl burner model is utilized to examine the effect of swirl angle θ and swirl length L of the swirler on the combustion behavior of hydrogen-enriched natural gas in a swirl burner. The results indicate that the swirl angle θ and swirl length L play an essential role in the combustion of natural gas containing hydrogen. As the swirl angle θ increases the flame temperature decreases more slowly the combustion becomes more stable and the length of the flame is slightly increased. Simultaneously CO and NO emissions will gradually decrease and the combustion effect is enhanced when the swirl angle is 45◦. With increased swirl length L the flame length grows the high-temperature region expands and CO and NO emissions decrease. Meanwhile the change in swirl length has little effect on the increase of flame peak temperature when the fuel is thoroughly mixed. When the swirl length is 12 mm CO and NO emissions are lower and NO emissions are reduced by 36.11% compared to a swirl length of 6 mm. This work is a reference point for applying hydrogen-mixed natural gas in the swirl burner but it must be studied and optimized further in future research.
Improvement of Temperature and Humidity Control of Proton Exchange Membrane Fuel Cells
Sep 2021
Publication
Temperature and humidity are two important interconnected factors in the performance of PEMFCs (Proton Exchange Membrane Fuel Cells). The fuel and oxidant humidity and stack temperature in a fuel cell were analyzed in this study. There are many factors that affect the temperature and humidity of the stack. We adopt the fuzzy control method of multi-input and multi-output to control the temperature and humidity of the stack. A model including a driver vehicle transmission motor air feeding electrical network stack hydrogen supply and cooling system was established to study the fuel cell performance. A fuzzy controller is proven to be better in improving the output power of fuel cells. The three control objectives are the fan speed control for regulating temperature the solenoid valve on/off control of the bubble humidifier for humidity variation and the speed of the pump for regulating temperature difference. In addition the results from the PID controller stack model and the fuzzy controller stack model are compared in this research. The fuel cell bench test has been built to validate the effectiveness of the proposed fuzzy control. The maximum temperature of the stack can be reduced by 5 ◦C with the fuzzy control in this paper so the fuel cell output voltage (power) increases by an average of approximately 5.8%.
Reversible Hydrogenation of AB2-type Zr–Mg–Ni–V Based Hydrogen Storage Alloys
Feb 2021
Publication
The development of hydrogen energy is hindered by the lack of high-efficiency hydrogen storage materials. To explore new high-capacity hydrogen storage alloys reversible hydrogen storage in AB2-type alloy is realized by using A or B-side elemental substitution. The substitution of small atomic-radius element Zr and Mg on A-side of YNi2 and partial substitution of large atomic-radius element V on B-side of YNi2 alloy was investigated in this study. The obtained ZrMgNi4 ZrMgNi3V and ZrMgNi2V2 alloys remained single Laves phase structure at as-annealed hydrogenated and dehydrogenated states indicating that the hydrogen-induced amorphization and disproportionation was eliminated. From ZrMgNi4 to ZrMgNi2V2 with the increase of the degree of vanadium substitution the reversible hydrogen storage capacity increased from 0.6 wt% (0.35H/M) to 1.8 wt% (1.0H/M) meanwhile the lattice stability gradually increased. The ZrMgNi2V2 alloy could absorb 1.8 wt% hydrogen in about 2 h at 300 K under 4 MPa H2 pressure and reversibly desorb the absorbed hydrogen in approximately 30 min at 473 K without complicated activation process. The prominent properties of ZrMgNi2V22 elucidate its high potential for hydrogen storage application.
Temperature Effect on the Mechanical Properties of Liner Materials used for Type IV Hydrogen Storage Tanks
Sep 2021
Publication
Type IV hydrogen storage tanks play an important role in hydrogen fuel cell vehicles (HFCVs) due to their superiority of lightweight good corrosion and fatigue resistance. It is planned to be used between -40℃ and 85℃ at which the polymer liner may have a degradation of mechanical properties and buckling collapse. This demand a good performance of liner materials in that temperature range. In this article the temperature effect on mechanical properties of polyamide 6 (PA6) liner material including specimens with weld seam was investigated via the stress-strain curve (S-S curve) macroscopic and microscopic morphology. Considering that the mechanical properties will change after the liner molding process this test takes samples directly from the liner. Results show that the tensile strength and tensile modulus increased by 2.46 times and 10.6 times respectively with the decrease of temperature especially in the range from 50℃ to -90℃. For the elongation at break and work of fracture they do not monotonously increase with the temperature up. Both of them reduce when the temperature rises from 20°C to 50°C especially for the work of fracture decreasing by 63%. The weld seam weakens the mechanical properties and the elongation at break and work of fracture are more obvious which are greater than 40% at each temperature. In addition the SEM images indicate that the morphology of fracture surface at -90°C is different from that at other temperatures which is a sufficient evidence of toughness reducing in low temperature.
Recent Advances in Hybrid Water Electrolysis for Energy-saving Hydrogen Production
Nov 2022
Publication
Electricity-driven water splitting to convert water into hydrogen (H2) has been widely regarded as an efficient approach for H2 production. Nevertheless the energy conversion efficiency of it is greatly limited due to the disadvantage of the sluggish kinetic of oxidation evolution reaction (OER). To effectively address the issue a novel concept of hybrid water electrolysis has been developed for energy– saving H2 production. This strategy aims to replace the sluggish kinetics of OER by utilizing thermodynamically favorable organics oxidation reaction to replace OER. Herein recent advances in such water splitting system for boosting H2 evolution under low cell voltage are systematically summarized. Some notable progress of different organics oxidation reactions coupled with hydrogen evolution reaction (HER) are discussed in detail. To facilitate the development of hybrid water electrolysis the major challenges and perspectives are also proposed.
Optimized Configuration and Operating Plan for Hydrogen Refueling Station with On-Site Electrolytic Production
Mar 2022
Publication
Hydrogen refueling stations (HRSs) are critical for the popularity of hydrogen vehicles (fuel cell electric vehicles—FCEVs). However due to high installation investment and operating costs the proliferation of HRSs is difficult. This paper studies HRSs with on-site electrolytic production and hydrogen storage devices and proposes an optimization method to minimize the total costs including both installation investment and operating costs (OPT-ISL method). Moreover to acquire the optimization constraints of hydrogen demand this paper creatively develops a refueling behavior simulation method for different kinds of FCEVs and proposes a hydrogen-demand estimation model to forecast the demand with hourly intervals for HRS. The Jensen–Shannon divergence is applied to verify the accuracy of the hydrogen-demand estimation. The result: 0.029 is much smaller than that of the estimation method in reference. Based on the estimation results and peak-valley prices of electricity from the grid a daily hydrogen generation plan is obtained as well as the optimal capacities of electrolyzers and storage devices. As for the whole costs compared with previous configuration methods that only consider investment costs or operating costs the proposed OPT-ISL method has the least 8.1 and 10.5% less respectively. Moreover the proposed OPT-ISL method shortens the break-even time for HRS from 11.1 years to 7.8 years a decrease of 29.7% so that the HRS could recover its costs in less time.
Fuel Cell Power Systems for Maritime Applications: Progress and Perspectives
Jan 2021
Publication
Fuel cells as clean power sources are very attractive for the maritime sector which is committed to sustainability and reducing greenhouse gas and atmospheric pollutant emissions from ships. This paper presents a technological review on fuel cell power systems for maritime applications from the past two decades. The available fuels including hydrogen ammonia renewable methane and methanol for fuel cells under the context of sustainable maritime transportation and their pre-processing technologies are analyzed. Proton exchange membrane molten carbonate and solid oxide fuel cells are found to be the most promising options for maritime applications once energy efficiency power capacity and sensitivity to fuel impurities are considered. The types layouts and characteristics of fuel cell modules are summarized based on the existing applications in particular industrial or residential sectors. The various research and demonstration projects of fuel cell power systems in the maritime industry are reviewed and the challenges with regard to power capacity safety reliability durability operability and costs are analyzed. Currently power capacity costs and lifetime of the fuel cell stack are the primary barriers. Coupling with batteries modularization mass production and optimized operating and control strategies are all important pathways to improve the performance of fuel cell power systems.
Study on the Effect of Second Injection Timing on the Engine Performances of a Gasoline/Hydrogen SI Engine with Split Hydrogen Direct Injecting
Oct 2020
Publication
Split hydrogen direct injection (SHDI) has been proved capable of better efficiency and fewer emissions. Therefore to investigate SHDI deeply a numerical study on the effect of second injection timing was presented at a gasoline/hydrogen spark ignition (SI) engine with SHDI. With an excess air ratio of 1.5 five different second injection timings achieved five kinds of hydrogen mixture distribution (HMD) which was the main factor affecting the engine performances. With SHDI since the HMD is manageable the engine can achieve better efficiency and fewer emissions. When the second injection timing was 105◦ crank angle (CA) before top dead center (BTDC) the Pmax was the highest and the position of the Pmax was the earliest. Compared with the single hydrogen direct injection (HDI) the NOX CO and HC emissions with SHDI were reduced by 20% 40% and 72% respectively.
Numerical Simulation of Hydrogen Leakage from Fuel Cell Vehicle in an Outdoor Parking Garage
Aug 2021
Publication
It is significant to assess the hydrogen safety of fuel cell vehicles (FCVs) in parking garages with a rapidly increased number of FCVs. In the present work a Flame Acceleration Simulator (FLACS) a computational fluid dynamics (CFD) module using finite element calculation was utilized to predict the dispersion process of flammable hydrogen clouds which was performed by hydrogen leakage from a fuel cell vehicle in an outdoor parking garage. The effect of leakage diameter (2 mm 3 mm and 4 mm) and parking configurations (vertical and parallel parking) on the formation of flammable clouds with a range of 4–75% by volume was considered. The emission was assumed to be directed downwards from a Thermally Activated Pressure Relief Device (TPRD) of a 70 MPa storage tank. The results show that the 0.7 m parking space stipulated by the current regulations is less than the safety space of fuel cell vehicles. Compared with a vertical parking configuration it is safer to park FCVs in parallel. It was also shown that release through a large TPRD orifice should be avoided as the proportion of the larger hydrogen concentration in the whole flammable domain is prone to more accidental severe consequences such as overpressure.
Reliability Analysis of Pyrotechnic Igniter for Hydrogen-Oxygen Rocket Engine with Low Temperature Combustion Instability Failure Mode
Mar 2022
Publication
To evaluate the functional reliability of the pyrotechnic igniter in the failure mode of unstable combustion at low temperature a reliability and reliability sensitivity analysis method based on the combination of an interior ballistic model and Kriging reliability method is proposed. Through the deterministic interior ballistic simulation the failure mode of low temperature unstable combustion of the pyrotechnic igniter is examined while the random variables are introduced to establish the ignition nonlinear implicit function of the pyrotechnic igniter. The ignition display function of the pyrotechnic igniter is established by the Kriging model which avoids the repeated calculation of true limit state function values. This study provides an efficient approach to evaluate the ignition reliability of the pyrotechnic igniter and compared with the traditional Monte Carlo method to verify the accuracy of the results. Finally reliability-based sensitivity indices are presented to quantify the significance of random parameters. It is shown that the influence of the uncertainties can be precisely described and the diameter of the nozzle plays a dominant role in ignition reliability. Additionally ignition experiments of nozzles with different diameters were performed to verify the result of sensitivity. This can further support the detailed design of the pyrotechnic igniter
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