Optimization of hydrogen feeding procedure in PEM fuel cell systems for transportation

The hydrogen feeding sub-system is one of balance of plant (BOP) components necessary for the correct operation of a fuel cell system (FCS). In this paper the performance of a 6 kW PEM (Proton Exchange Membrane) FCS, able to work with two fuel feeding procedures (dead-end or flow-through), was experimentally evaluated with the aim to highlight the effect of the anode operation mode on stack efficiency and durability. The FCS operated at low reactant pressure (<50 kPa) and temperature (<330 K), without external humidification. The experiments were performed in both steady state and dynamic conditions. The performance of some cells in dead-end mode worsened during transient phases, while a more stable working was observed with fuel recirculation. This behavior evidenced the positive role of the flow-through procedure in controlling flooding phenomena, with the additional advantage to simplify the management issues related to hydrogen purge and air stoichiometric ratio. The flow-through modality resulted a useful way to optimize the stack efficiency and to reduce the risks of fast degradation due to reactant starvation during transient operative phases.     

NOx formation in post-flame gases from syngas/air combustion at atmospheric pressure

Species concentration measurements specifically those associated with nitrogen oxides (NO_x) can act as important validation targets for developing kinetic models to predict NO_x emissions under syngas combustion accurately. In the present study, premixed combustion of syngas/air mixtures, with equivalence ratio (Φ) from 0.5 to 1.0 and H₂/CO ratio from 0.25 to 1.0 was conducted in a McKenna burner operating at atmospheric pressure. Temperature and NO_x concentrations were measured in the post-combustion zone. For a given H₂/CO ratio, increasing the equivalence ratio from lean to stoichiometric resulted in an increase in NO and decrease in NO₂ concentration near the flame. Increasing the H₂/CO ratio led to a decrease in the temperature as well as the NO concentration near the flame. Based on the axial profiles above the burner, NO concentration increases right above the flame while NO₂ concentration decreases through NO₂-NO conversion reactions according to the path flux analysis. In addition, the present experiments were operated in the laminar region where multidimensional transport effects play significant roles. In order to account for the radial and axial diffusive and convective coupling to chemical kinetics in laminar flow, a multidimensional model was developed to simulate the post-combustion species and temperature distribution. The measurements were compared against both multidimensional computational fluid dynamics (CFD) simulations and one-dimensional burner-stabilized flame simulations. The multidimensional model predictions resulted in a better agreement with the measurements, clearly highlighting the effect of multidimensional transport.     

Advanced control of grid-connected inverters for proton exchange membrane fuel cell system

Voltage support is one of the most important issues for operating grid-connected inverters under grid faults. Many control strategies have been addressed in literature, but most of them focus on the voltage support control without considering issues of power quality due to voltage harmonics. In order to sort out the drawback, a novel advanced control strategy is presented in this paper. It is able to provide the voltage support function. Meanwhile, the power quality is improved by regulating the control coefficients. The time-domain simulation and experimental results are provided to evaluate the conventional and proposed control strategies. The results show that the total harmonic distortion of PCC voltage can be reduced from 9.35% to 2.88% with the proposed solution. Meanwhile, the voltage support is also achieved, which verify the effectiveness of the proposed solution.     

Fuzzy control of hydrogen pressure in fuel cell system

Precise control of hydrogen pressure is crucial for the performance and durability of fuel cell systems. With the widely used common-rail injection system, traditional PID controller still dominates. For a long time, the hydrogen pressure fluctuates acutely when hydrogen purge valve switches or load sharply changes with using PID controller. In recent studies, several new control strategies are presented. However, mostly of them are theoretical and experimental. In this study, an improved common-rail injection system, hydrogen injector/ejector assembly is introduced. Based on a real fuel cell system, a Mamdani fuzzy controller is designed to regulate the hydrogen pressure. The algorithm of fuzzy controller is explained in detail. A comparative study is carried out between fuzzy controller and PID controller. According to the results, the stability of hydrogen pressure with using fuzzy controller is better than using PID controller. This research could be useful for the control of fuel cell system.     

Premixed ammonia/hydrogen swirl combustion under rich fuel conditions for gas turbines operation

Energy storage is one of the highest priority challenges in transitioning to a low-carbon economy. Fluctuating, intermittent primary renewable sources such as wind and solar require low-carbon storage options to enable effective load matching, ensuring security of supply. Chemical storage is one such option, with low or zero carbon fuels such as hydrogen, alcohols and ammonia having been proposed. Ammonia provides zero-carbon hydrogen storage whilst offering liquefaction at relatively low pressures and atmospheric temperatures, enabling ease of transportation in a pre-existing infrastructure. Ammonia can also be used directly as a fuel in power plants such as gas turbines to avoid complete conversion back to hydrogen. It is a relatively unreactive fuel, and so it is of interest to explore the potential utilisation of ammonia/hydrogen mixtures. Hence, the goal of this paper is to provide a first assessment of the suitability of a chosen 70%NH₃30%H₂ (%vol) blend for utilisation within a gas turbine environment, based on primary combustion diagnostics including combustion stability – via OH chemiluminescence - and emissions (NO_x and NH₃). An established optical generic swirl-burner enabled studies of the influence of equivalence ratio (φ > 1), ambient temperature (<484 ± 10 K) and bypass air, with a focus on NO_x reduction, one of the main challenges for ammonia combustion. A numerical GT cycle model is developed alongside the experimental investigation. The results demonstrate that the blend has considerable potential as a fuel substitute with reasonable combustion stability and significant reduction of emissions for the cases without bypass air, due to increased chemical reactivity of unburned ammonia. However, emissions are still above those recommended for gas turbine cycles, with a theoretical cycle that still produces low efficiencies compared to DLN methane, highlighting the requirement for new injection techniques to reduce NO_x/unburned NH₃ in the flue gases whilst ensuring increased power outputs.     

Bifurcation analysis of the effect of hydrogen addition on the dynamic behavior of lean premixed pre-vaporized ethanol combustion

In this work, a mathematical model of fuel conversion and energy balance has been developed to study the dynamic behavior of a lean premixed pre-vaporized combustor fed with ethanol/air and ethanol–hydrogen/air mixtures. The combustor was modeled as a well stirred reactor (WSR). Results show that, for a simplified model reaction, Hopf bifurcations occur. Spontaneous oscillations have been found, suggesting that the combustion reaction plays an important role in the development of dynamic regimes. Hydrogen addition stabilizes ethanol combustion, damping the oscillations.     

Development of a dynamic regenerative fuel cell system

The development of a regenerative Integrated Renewable Energy Experiment (IRENE) is presented. IRENE is a laboratory-scale distributed energy system with a modular structure which can be re-configured to test newly developed components for generic regenerative systems integrating renewable energy, electrolysis, hydrogen and electricity storage and fuel cells. A special design feature of this test bed is the ability to accept transient inputs from and provide transient loads to real devices as well as from simulated energy sources/sinks. The findings of this study should be of interest to developers of small-scale renewable-regenerative systems intended to displace fossil fuel systems.     

Optimization of fuel cell system operating conditions for fuel cell vehicles

Proton exchange membrane fuel cell (PEMFC) technology for use in fuel cell vehicles and other applications has been intensively developed in recent decades. Besides the fuel cell stack, air and fuel control and thermal and water management are major challenges in the development of the fuel cell for vehicle applications. The air supply system can have a major impact on overall system efficiency. In this paper a fuel cell system model for optimizing system operating conditions was developed which includes the transient dynamics of the air system with varying back pressure. Compared to the conventional fixed back pressure operation, the optimal operation discussed in this paper can achieve higher system efficiency over the full load range. Finally, the model is applied as part of a dynamic forward-looking vehicle model of a load-following direct hydrogen fuel cell vehicle to explore the energy economy optimization potential of fuel cell vehicles.     

Critical issues in heat transfer for fuel cell systems

The current state of the art in fuel cell system development will be reviewed with an emphasis of the critical issues on heat transfer.

The heat transfer issues for both PEM based systems and SOFC based fuel cell systems will be addressed.

For systems that are based on hydrocarbon fuels a reforming step is needed and critical heat transfer issues are also present in this fuel processing part of the system where the primary feedstock is converted to reformate. Also, in both the PEM and SOFC fuel cell itself, heat transfer is a critical issue. It will be shown what are the implications of the fuel cell heat transfer to the total system architecture for the various fuel cell applications (stationary power, transport).

The heat transfer issues in fuel cell system development will be clarified with several examples.     

Comments on solid state hydrogen storage systems design for fuel cell vehicles

In recent years, significant research and development efforts were spent on hydrogen storage technologies with the goal of realizing a breakthrough for fuel cell vehicle applications. This article scrutinizes design targets and material screening criteria for solid state hydrogen storage. Adopting an automotive engineering point of view, four important, but often neglected, issues are discussed: 1) volumetric storage capacity, 2) heat transfer for desorption, 3) recharging at low temperatures and 4) cold start of the vehicle. The article shall help to understand the requirements and support the research community when screening new materials.     

Development of a hydrogen dual sensor for fuel cell applications

The development and application of a hydrogen dual sensor (HDS) for the application in the fuel cell (FC) field, is reported. The dual sensing device is based on a ceramic platform head with a semiconducting metal oxide layer (MOx) printed on Pt interdigitated contacts on one side and a Pt serpentine resistance on the back side. MOx layer acts as a conductometric (resistive) gas sensor, allowing to detect low H₂ concentrations in air with high sensitivity and fast response, making it suitable as a leak hydrogen sensor. The proposed Co-doped SnO₂ layer shows high sensitivity to hydrogen (R₀/R = 90, for 2000 ppm of H₂) at 250 °C in air, and with fast response (<3 s). Pt resistance serves as a thermal conductivity sensor, and can used to monitor the whole range of hydrogen concentration (0–100%) in the fuel cell feed line with short response-recovery times, lower than 13 s and 14 s, respectively. The effect of the main functional parameters on the sensor response have been evaluated by bench tests. The results demonstrate that the dual sensor, in spite of its simplicity and cheapness, is promising for application in safety and efficiency control systems for FC power source.     

Air mass flow and pressure optimisation of a PEM fuel cell range extender system

In order to eliminate the local CO₂ emissions from vehicles and to combat the associated climate change, the classic internal combustion engine can be replaced by an electric motor. The two most advantageous variants for the necessary electrical energy storage in the vehicle are currently the purely electrochemical storage in batteries and the chemical storage in hydrogen with subsequent conversion into electrical energy by means of a fuel cell stack. The two variants can also be combined in a battery electric vehicle with a fuel cell range extender, so that the vehicle can be refuelled either purely electrically or using hydrogen. The air compressor, a key component of a PEM fuel cell system, can be operated at different air excess and pressure ratios, which influence the stack as well as the system efficiency. To asses the steady state behaviour of a PEM fuel cell range extender system, a system test bench utilising a commercially available 30 kW stack (96 cells, 409 cm² cell area) was developed. The influences of the operating parameters (air excess ratio 1.3 to 1.7, stack temperature 20 °C–60 °C, air compressor pressure ratio up to 1.67, load point 122 mA/cm² to 978 mA/cm²) on the fuel cell stack voltage level (constant ambient relative humidity of 45%) and the corresponding system efficiency were measured by utilising current, voltage, mass flow, temperature and pressure sensors. A fuel cell stack model was presented, which correlates closely with the experimental data (0.861% relative error). The air supply components were modelled utilising a surface fit. Subsequently, the system efficiency of the validated model was optimised by varying the air mass flow and air pressure. It is shown that higher air pressures and lower air excess ratios increase the system efficiency at high loads. The maximum achieved system efficiency is 55.21% at the lowest continuous load point and 43.74% at the highest continuous load point. Future work can utilise the test bench or the validated model for component design studies to further improve the system efficiency.     

Efficiencies of hydrogen storage systems onboard fuel cell vehicles

Energy efficiency, vehicle weight, driving range, and fuel economy are compared among fuel cell vehicles (FCV) with different types of fuel storage and battery-powered electric vehicles. Three options for onboard fuel storage are examined and compared in order to evaluate the most energy efficient option of storing fuel in fuel cell vehicles: compressed hydrogen gas storage, metal hydride storage, and onboard reformer of methanol. Solar energy is considered the primary source for fair comparison of efficiencies for true zero emission vehicles. Component efficiencies are from the literature. The battery powered electric vehicle has the highest efficiency of conversion from solar energy for a driving range of 300 miles. Among the fuel cell vehicles, the most efficient is the vehicle with onboard compressed hydrogen storage. The compressed gas FCV is also the leader in four other categories: vehicle weight for a given range, driving range for a given weight, efficiency starting with fossil fuels, and miles per gallon equivalent (about equal to a hybrid electric) on urban and highway driving cycles.     

The fuel cell electric vehicles: The highlight review

Transportation sector is the important sector and consumed the most fossil fuel in the world. Since COVID-19 started in 2019, this sector had become the world connector because every country relies on logistics. The transportation sector does not only deal with the human transportation but also relates to logistics. Research in every country has searched for alternative transportation to replace internal combustion engines using fossil fuel, one of the most prominent choices is fuel cells. Fuel cells can use hydrogen as fuel. Hydrogen can be fed to the fuel cells to provide electric power to drive vehicles, no greenhouse gas emission and no direct combustion required. The fuel cells have been developed widely as the 21st century energy-conservation devices for mobile, stationary, and especially vehicles. The fuel cell electric vehicles using hydrogen as fuel were also called hydrogen fuel cell vehicles or hydrogen electric vehicles. The fuel cells were misconceived by several people that they were batteries, but the fuel cells could provide electric power continuously if their fuel was provided continuously. The batteries could provide electric power as their only capacities, when all ions are released, no power could be provided. Because the fuel cell vehicles play important roles for our future transportation, the overall review for these vehicles is significantly interesting. This overall review can provide general and technical information, variety of readers; vehicle users, manufacturers, and scientists, can perceive and understand the fuel cell vehicles within this review. The readers can realize how important the fuel cell technologies are and support research around the world to drive the fuel cell vehicles to be the leading vehicles in our sustainable developing world.     

Dynamic modelling of PEM fuel cell system for simulation and sizing of marine power systems

This article presents a model of a proton exchange membrane fuel cell (PEMFC) system for marine power systems. PEMFC in marine hybrid power sources can have various power ranges and capacities in contrast with vehicle applications. Investigating PEMFCs behaviour and performance for various conditions and configurations is demanded for proper sizing and feasibility studies. Hence, modelling and simulation facilitate understanding the performance of the PEMFC behaviour with various sizes and configurations in power systems. The developed model in this work has a system level fidelity with real time capabilities, which can be utilized for simulator approaches besides quasi-static studies with a power-efficiency curve. Moreover, the model can be used for scaling the PEMFC power range by considering transient responses and corresponding efficiencies. The Bond graph approach as a multi-disciplinary energy based modelling strategy is employed for the PEMFC as a multi domains system. In the end, various PEMFC cell numbers and compressor sizes have been compared with power-efficiency curves and transient responses in a benchmark.     

Evaluation of a low temperature fuel cell system for residential CHP

CHP (combined heat and power) is a technology that allows to provide electrical and thermal energy. CHP is normally used in systems that produce wasted heat at high temperature to recover energy and increase overall system efficiency. The aim of this work is to investigate the possibility to recover heat produced by a 5 kW PEFC system for residential applications (hot water and building heating). As known, PEFCs work at low temperature (60-90 °C) and the experiments have been carried out in order to improve the overall system efficiency by reusing heat that is normally wasted.The work was developed during an Italian National project PNR-FISR “Polymeric and Ceramic Fuel Cell” coordinated by CNR-ITAE. A 5 kW PEFC system, developed with NUVERA Fuel Cells in the framework of the project, was tested in cogeneration configuration recovering wasted heat with a heat exchanger directly connected to cathode out.Tests on PEFC system were carried out in the range 2.5-5 kW, maintaining the working stack temperature at 71 °C. Heat, produced at different power levels, was removed from the system by using a regulated water flow in the heat exchanger. A peculiar feature of the system is the so-called “direct water injection” at the cathode, that allows simultaneous cooling and humidification of the stack. This characteristic permitted the recovery of most of the waste heat produced by the fuel cell.The performance of the PEFC unit was analyzed in terms of electrical, thermal and total efficiency. Tests showed that it is possible to obtain water at about 68 °C under different power levels. Moreover, experimental data showed that heat recovered was maximum when heat exchanger worked at nominal power and, under these conditions, the overall system efficiency increased up to 85%.     

A robust cell voltage monitoring system for analysis and diagnosis of fuel cell or battery systems

Cell voltage monitoring (CVM) systems are essential for the operation of fuel cell stacks and some battery systems, in the field as well as in the laboratory, because they allow the diagnosis and correction of problems that would otherwise go unnoticed and cause impaired performance or even permanent damage. A robust, safe, and low-cost design for a CVM unit is presented, using electromechanical relays as multiplexing switches. Some examples from the application of the unit on the University of Delaware's fuel cell battery hybrid buses are presented, including its use in automatically correcting anode flooding and diagnosing air channel blockage.     

A fuzzy logic PI control with feedforward compensation for hydrogen pressure in vehicular fuel cell system

In a vehicular fuel cell system, alternative load and frequent purge action can lead to anode pressure varies with the hydrogen mass flow fluctuation. It's crucial to control the pressure difference between anode and cathode within a reasonable range to avoid adverse phenomena such as membrane failure, reactant starvation, or even water management fault. In this paper, an improved proportional integrative (PI) controller by the fuzzy logic technique that considers the engineer experience and knowledge on the hydrogen supply system behavior is proposed for hydrogen pressure control, in which the PI parameters are tuned by a fuzzy decision process. Furthermore, load current and purge action regarded as input disturbances are applied for feedforward compensation to reduce the pressure response hysteresis. A hydrogen supply subsystem based on the proportional valve is modeled, and corresponding parameters are determined by analyzing the response time and steady pressure fluctuation. The performance of the conventional PI controller, the fuzzy logic PI (FLPI) controller and fuzzy logic PI with feedforward (FLPIF) controller is validated. The presented results indicated that the FLPI controller significantly improves the dynamic response of hydrogen pressure compared to the PI controller, and the FLPIF controller can further reduce overshoot caused by disturbance. Finally, the proposed FLPIF controller is implemented on a rapid prototype platform of the hydrogen supply subsystem and an actual fuel cell system, exhibiting satisfactory performance.     

Demonstration and development of a polymer electrolyte fuel cell system for residential use

Fuel cell systems, especially those fed with hydrogen, have reached considerable performance targets in laboratory conditions with constant loads and conservative environmental conditions. However, a check of the potential of such systems in real conditions is necessary, particularly in terms of varying electrical and thermal loads and of more severe climatic conditions.To determine the state of the art of such technology and to develop systems capable of supporting future national energy scenarios within the PNR-FISR project, “Polymeric electrolytes and ceramic fuel cells: demonstration of systems and development of new materials,” the development of fuel cell systems ranging from 1 to 5 kW of power and based on either solid polymer (PEMFC) or solid oxide (SOFC) technology are in progress. In this paper, the demonstration of a pre-commercial PEMFC system fed with hydrogen and developed in cooperation with NUVERA is described. The system has been developed in order to determine its limits and capacity in relation to start-up time, response time, consumption, efficiency, reliability, etc. It has currently reached 1000 working hours of continuous performance with variable loads that simulate those of a typical residential dwelling.