Search Results (6)

The exhaust purge on the anode side is a critical step in the operation of fuel cell systems, and optimizing the exhaust interval time is essential for enhancing stack efficiency and hydrogen utilization. This paper proposed a method to determine the purge strategy of hydrogen supply system based on theoretical and simulation analysis. To investigate the impact of anode purge strategy on the performance of automotive fuel cells, a model of a 100 kW fuel cell stack and a dual-ejector hydrogen supply system was developed in MATLAB/Simulink(R2022b) using principles of fluid dynamics, simulation, and experimental data. This model effectively captures the accumulation and exhaust of hydrogen, nitrogen, and vapor within the anode. Simulations were conducted under seven different exhaust interval times at varying current densities to study the effect of exhaust interval on the performance of the fuel cell. The results indicate that for a 100 kW fuel cell, the exhaust interval time should be controlled within 25 s and should decrease as the current density increases. At low current density, increasing the exhaust interval has a more significant effect on improving hydrogen utilization. At high current density, reducing the exhaust interval helps maintain a stable hydrogen excess ratio and shortens the time required for the output voltage to reach a stable state. Full article

This study introduces a novel linear segmentation method to optimize the nitrogen purge strategy for proton exchange membrane fuel cells (PEMFCs) operating in an anode recirculation mode. The method simplifies the design of purge cycles by eliminating the need for complex mathematical modeling and multivariable optimization, making it more suitable for industrial applications while avoiding the need for lengthy orthogonal experiments. By experimentally determining the maximum tolerable nitrogen accumulation time and leveraging the linear relationship between nitrogen accumulation and purge duration, the traditional long-cycle purge process is divided into multiple short cycles, establishing an optimal nitrogen discharge strategy. Experimental results demonstrate that the segmented purge cycles significantly reduce voltage fluctuations and improve voltage uniformity across cells. Notably, using a purge threshold with a 30 s closing time and a 2 s opening time resulted in a 19.8% improvement in voltage uniformity. In addition, a detailed analysis of the hydrogen consumption during the purge cycle reveals that an excessive purge frequency leads to significant hydrogen losses, whereas prolonged purge cycles may allow nitrogen accumulation to adversely affect voltage stability. By balancing these effects, the proposed strategy maintains the operational efficiency within the ideal range of 50–60%. Full article

The measurement of hydrogen concentration in fuel cell systems is an important prerequisite for the development of a control strategy to enhance system performance, reduce purge losses and minimize fuel cell aging effects. In this perspective paper, the working principles of hydrogen sensors are analyzed and their requirements for hydrogen control in fuel cell systems are critically discussed. The wide measurement range, absence of oxygen, high humidity and limited space turn out to be most limiting. A perspective on the development of hydrogen sensors based on palladium as a gas-sensitive metal and based on the organic magnetic field effect in organic light-emitting devices is presented. The design of a test chamber, where the sensor response can easily be analyzed under fuel cell-like conditions is proposed. This allows the generation of practical knowledge for further sensor development. The presented sensors could be integrated into the end plate to measure the hydrogen concentration at the anode in- and outlet. Further miniaturization is necessary to integrate them into the flow field of the fuel cell to avoid fuel starvation in each single cell. Compressed sensing methods are used for more efficient data analysis. By using a dynamical sensor model, control algorithms are applied with high frequency to control the hydrogen concentration, the purge process, and the recirculation pump. Full article

The anode recirculation mode is increasingly being adopted in today’s fuel cell systems. The recycling of hydrogen gas can effectively improve fuel utilization and the wider economy. However, using the purge strategy for the recirculation exhaust has a significant impact on the operational performance and economic efficiency of fuel cell systems.Experiments have shown that, when the purge interval increases from 6 s to 10 s, the recirculation pump power increases by about 20%, the nitrogen content in the exhaust gas increases, and the stack voltage shows a 10 V attenuation. The accumulation of nitrogen permeation in the anode circuit leads to the degradation of the fuel cell performance. Therefore, it is necessary to discharge the accumulated nitrogen through the purge valve in a timely manner. However, opening the exhaust valve with excessively high frequency can result in the unreacted hydrogen being discharged, which reduces the economic efficiency of the fuel cell. This paper is based on the principle of mass conservation and models each subsystem of the anode circuit in the recirculation pump mode of the fuel cell separately, including the proportional valve model, the hydrogen consumption model of the fuel cell, the nitrogen permeation model of the fuel cell, the neural network model of the circulating pump, and the purge valve model. These submodels are integrated to construct a nitrogen content observer for the hydrogen circuit, which can estimate the nitrogen content. The accuracy of the model is validated through experimental data. The estimation error is less than 5.5%. The nitrogen content in the anode circuit can be effectively estimated, providing a model reference for purge operations and improving hydrogen utilization. Full article

During the shutdown process of the fuel cell system for vehicles, the air entering the anode chamber can form the hydrogen/air interface, accelerating the carbon corrosion of the catalytic layer. According to optimized control strategies, the carbon corrosion of fuel cells can be reduced. Nowadays, the main control strategies include gas purging and the consumption of residual oxygen in the stack by the auxiliary load. However, the oxygen in the fuel cell stack cannot be fully consumed or can cause the single-cell voltage to rise to 0.8 V with an inappropriate discharge current drop rate and auxiliary load resistance value, thus affecting the protective effect of the shutdown strategy. In this work, a shutdown strategy of the fuel cell system is studied. After the experiment, the optimized value of the discharge current drop rate and the auxiliary load resistance were obtained. With the resistance value of 50 Ω and the current drop rate of 7 A/s, the shutdown time of the fuel cell system is 13.5 s and the time of single-cell voltage above 0.82 V in the fuel cell stack is 0.1 s. Thus, the optimized shutdown strategy can reduce the shutdown time. Full article

In this report, a 5 kW PEFC system running on dry hydrogen with an appropriately sized Balance of Plant (BoP) was used to conduct experimental studies and analyses of gas supply subsystems. The improper rating and use of BoP components has been found to increase parasitic loads, which consequently has a direct effect on the polymer electrolyte fuel cell (PEFC) system efficiency. Therefore, the minimisation of parasitic loads while maintaining desired performance is crucial. Nevertheless, little has been found in the literature regarding experimental work on large stacks and BoP, with the majority of papers concentrating on modelling. A particular interest of our study was the anode side of the fuel cell. Additionally the rationale behind the use of hydrogen anode recirculation was scrutinised, and a novel anode purging strategy was developed and implemented. Through experimental modelling, the use of cathode air blower was minimised since it was found to be the biggest contributor to the parasitic loads. Full article