Coolant controls of a PEM fuel cell system

When operating the polymer electrolyte membrane (PEM) fuel cell stack, temperatures in the stack continuously change as the load current varies. The temperature directly affects the rate of chemical reactions and transport of water and reactants. Elevated temperature increases the mobility of water vapor, which reduces the ohmic over-potential in the membrane and eases removal of water produced. Adversely, the high temperature might impose thermal stress on the membrane and cathode catalyst and cause degradation. Conversely, excessive supply of coolants lowers the temperature in the stack and reduces the rate of the chemical reactions and water activity. Corresponding parasitic power dissipated at the electrical coolant pump increases and overall efficiency of the power system drops.     

Unsteady 2D PEM fuel cell modeling for a stack emphasizing thermal effects

Models currently used for analyses of thermal and water behavior of a PEM fuel cell are based 3D computational fluid dynamics (CFD). However, the analyses are limited to a single cell with static behavior. Thus, these models cannot be used for analyses of dynamic behavior of a stack that continuously varies according to operating conditions. The model proposed describes dynamic behavior of a stack with two adjoining cells and endplate assembly, and work as a current controlled voltage source that can be used for optimization of BOPs and the associated controls. Simulations have been conducted to analyze start-up behaviors and the performance of the stack. Our analyses deliver following results: (1) dynamic temperature distribution in both the through-plane direction and the along channel direction of the fuel cell stack, (2) effects influencing the source terms of current density, and (3) dynamic oxygen concentration distribution. The temperature profile and its variation propensity are comparable to the previous results [Y. Shan, S.Y. Choe, J. Power Sources, 145 (1) (2005) 30–39; Y. Shan, S.Y. Choe, J. Power Sources, in press].     

The energy performance improvement of a PEM fuel cell with various chaotic flowing channels

To improve the energy performance of a proton exchange membrane fuel cell (PEMFC), novel chaotic structures are proposed and numerically evaluated for replacing straight types in the serpentine gas diffusion flow channels. The numerical model is verified by the available experimental data. Nine cases (chaotic channels, Cases A2, B1, B2, C1, C2, D1, D2, E1, and E2) and a baseline case (straight flow channel, Case A1) are evaluated, and the detailed temperature and the flow characteristics are presented and analyzed. The influences of the main design parameters including the corner angle, bends number, and datum surface number are also analyzed and concluded. It is found that the newly proposed chaotic structures can improve not only the temperature uniformity, but also the maximum output power and the energy efficiency of the PEMFC. Compared with a traditional PEMFC, the power output of the new PEMFCs with chaotic flowing channels can be improved by 6.26% and the efficiency of PEMFC can be promoted by 8.40%.     

Simultaneous thermal and visual imaging of liquid water of the PEM fuel cell flow channels

Water flooding and membrane dry-out are two major issues that could be very detrimental to the performance and/or durability of the proton exchange membrane (PEM) fuel cells. The above two phenomena are well-related to the distributions of and the interaction between the water saturation and temperature within the membrane electrode assembly (MEA). To obtain further insights into the relation between water saturation and temperature, the distributions of liquid water and temperature within a transparent PEM fuel cell have been imaged using high-resolution digital and thermal cameras. A parametric study, in which the air flow rate has been incrementally changed, has been conducted to explore the viability of the proposed experimental procedure to correlate the relation between the distribution of liquid water and temperature along the MEA of the fuel cell. The results have shown that, for the investigated fuel cell, more liquid water and more uniform temperature distribution along MEA at the cathode side are obtained as the air flow rate decreases. Further, the fuel cell performance was found to increase with decreasing air flow rate. All the above results have been discussed.     

Performance prediction of proton exchange membrane fuel cell engine thermal management system using 1D and 3D integrating numerical simulation

The cooling system of proton exchange membrane fuel cell (PEMFC) engine was simulated by 1D and 3D collaborative simulation method. Firstly, the resistance characteristics of the flow channel are obtained by simulating the airside flow model. A three-dimensional simulation model including dual fans and radiator is also established to simulate the airflow distribution. The one-dimensional simulation model of 30 kW PEMFC engine cooling system that are mainly composed of a thermostat, water pump, and fan and radiator model is established. Secondly, the heat dissipation performance of the cooling system is calculated by using the coupled simulation model. It is found that the simulation results of the amount of heat transferred are in good agreement with the experimental data by compromising, which proves that the model is reasonable. Finally, the thermal performance of the extreme operating conditions of the PEMFC system is simulated by means of a simulation model. By monitoring the flow of the pump and the fan speed, we can maintain the stack internal heat balances, so that the stack efficient and stable operation. The results demonstrate that the 3D simulation can get the distribution of fluid flow more accurately, while the simulation time of 1D thermal system is short and can guide the matching of heat transfer parts quickly.     

A method for evaluating the efficiency of PEM fuel cell engine

Efficiency is an important factor to reflect the performance of fuel cell engine (FCE). Evaluating efficiency should consider efficiency properties and common work conditions of FCE. In this paper, output power of FCE on real work conditions is analyzed according to driving cycles, and four efficiency evaluation points are obtained, as well as their weighted values. Then, a scoring function is used to convert the efficiency values of four evaluation points into scores. Multiplying scores by their weighted values and adding them together, we can get overall scores of efficiency properties. This method can evaluate the efficiency performance of FCE reasonably and objectively.     

Microcontroller-based emulation of a PEM fuel cell

This paper proposes an accurate and easy-to-implement emulator which is able to track the characteristic curve of a Proton Exchange Membrane Fuel Cell (PEMFC). Such an emulator is based on a low-cost microcontroller , isolated voltage and current sensors. The proposed emulator takes advantages of the flexibility and robustness. The sensed voltage and current provide to the microcontroller the accurate information to compute the output voltage of an actual PEMFC. The obtained voltage is sent to a digital-to-analog converter in order to command the continuous control voltage. The simplified electrochemistry model is presented and validated through simulation and then corroborated via experimentation. The proposed emulator is subjected to two load conditions: fixed load resistor and power electronic converter. The employed power converter is controlled by a variable duty cycle which is adjusted to a value at which the power extracted from the emulator is maximum.     

Automotive fuel cell engine test cell design and its thermal flow analysis

A test cell for automotive PEM fuel cell engine is introduced and designed. Similarities and differences of facilities between PEM fuel cell engine and inner-combustion engine are illustrated. It turns out that, the air treatment, exhaust gas, cooling and electrical facilities are quite similar, the fuel treatment, power load type, ventilation and air-conditioning are quite different, while the vibration isolation and noise elimination facilities are completely simplified. Furthermore, a thermodynamic model is proposed to analysis the heat flow in fuel cell engine test cell. The Monte Carlo Simulation method is applied to get the proportion of outgoing thermal flows. A thermal flow rule of 4.5/4.5/0.6/0.4 is proposed as rule of thumb for cell designer.     

Sparrow search algorithm applied to temperature control in PEM fuel cell systems

Working temperature is a critical parameter that influences the performance of proton exchange membrane fuel cells (PEMFCs). Appropriate thermal management can improve the efficiency of PEMFCs and prevent irreversible internal damage such as membrane degradation. To solve the slow response and poor dynamic performance of traditional temperature control strategies, the dynamic temperature mode of PEMFCs is established and a temperature control strategy based on the sparrow search algorithm-proportional integral differential (SSA-PID) is proposed in this study. The performance of the SSA-PID temperature control is verified by the simulations of current step change, vehicle dynamic load, and working parameter variation. The results show that the proposed method has the advantages of fast convergence, better dynamic performance, and anti-disturbance ability. The maximum power density of the SSA-PID temperature controller is 6.58% and 12.94% higher than GA (genetic algorithm)-PID and traditional PID controllers, respectively. Moreover, the proposed method can ensure temperature fluctuations within 0.5 K under dynamic disturbance.     

Development of a cylindrical PEM fuel cell

Proton exchange membrane fuel cells (PEMFCs) have strong potential as power conversion devices of the future, especially for man-portable and mobile applications. However, the manufacturing cost should be significantly reduced for making PEMFCs commercially attractive. An improvement of the power density with respect to the weight of the cell - termed as gravimetric power density in this study - can help in achieving lower manufacturing cost and reducing parasitic power losses, which is particularly important in man-portable applications. Furthermore, the power density of a PEMFC with respect to the overall volume of the cell - termed as volumetric power density in this study - must be improved for man-portable and automotive applications. The bipolar plates made out of graphite contribute significantly to the cost, weight, and volume of the cell. The state-of-the-art PEM fuel cells are of planar design. While several commercial planar prototypes have been demonstrated, cost and water management are still major issues. These problems arise partly as a result of the complicated bipolar plate design in planar PEMFC. Because the planar fuel cell concept has been so well-entrenched, alternate designs have not been seriously pursued. In this paper, we present some experimental studies on a novel cylindrical PEM fuel cell design that addresses the cost, gravimetric and volumetric power density issues. This study while highlighting the advantages of the tubular design also identifies areas of research that will have tremendous utility in further development of this technology.     

Performance study of a PEM fuel cell

This paper presents the installation, maintenance and the efficiency of a Polymer Electrolyte Membrane (PEM) fuel cell, Ballard Trade Mark that use pure hydrogen as fuel and air as an oxidant. A study of the overall efficiency, considering the co-generation of electrical and thermal energies, is performed. The system consists of the cell, a CC/CC converter, a battery, a DC/AC inverter and the load. The behavior of the system is experimentally analyzed for different load states (cases) by measuring and controlling all the parameters registered by the communication software of the cell. The software can adjust limit values for current intensity, hydrogen flow, pressure and the temperature.     

Computational analysis of fuel saving by using porous-end configuration for a PEM fuel cell

In the present study, a novel porous-end PEMFC inspired by the characteristics of open-end and dead-end PEMFCs is proposed for fuel saving. For this purpose, a porous media region with a certain thickness is added to the outlet region of the anode channel of an open-end PEMFC. The effect of porous media thickness at the anode channel on the current density and hydrogen mass flow was numerically analyzed. Results indicate that in comparison to the base model PEMFC, the presence of porous media at the end of the anode channel of porous-end PEMFC leads to an increase in the pressure and a decrease in the velocity magnitude in the anode channel. Results illustrate that the porous-end PEMFC with t = 1 mm thickness can be an adequate choice to gain an optimum design for the porous-end configuration. This conclusion becomes more highlighted when the results give the 66.17% reduction in fuel consumption.     

Study of thermal conductivity of PEM fuel cell catalyst layers

Thermal conductivities and compression of differently composed Polymer Electrolyte Membrane Fuel Cell (PEMFC) Catalyst Layers (CLs) were measured, both when dry and when containing liquid water. The results were compared using a 1-D thermal model.     

Exergetic performance analysis of a PEM fuel cell

In this paper we investigate the effects of thermodynamic irreversibilities on the exergetic performance of proton exchange membrane (PEM) fuel cells as a function of cell operating temperature, pressures of anode and cathode, current density, and membrane thickness. The practical operating conditions are selected to be 3–5 atm for anode and cathode pressures, and 323–353 K for the cell temperatures, respectively. In addition, the membrane thicknesses are chosen as 0.016, 0.018 and 0.02 cm, respectively. Moreover, the current density range of the PEM fuel cell is selected to be 0.01–2.0 A cm^?2. It is concluded that exergy efficiency of PEM fuel cell decreases with a rise in membrane thickness and current density, and increases with a rise of cell operating pressure and with a decrease of current density for the same membrane thickness. Thus, it can be said that, in order to increase the exergetic performance of PEM fuel cell, the lower membrane thickness, the lower current density and the higher cell operating pressure should be selected in case PEM fuel cell is operated at constant cell temperature. Copyright © 2005 John Wiley & Sons, Ltd.     

Experimental analysis of a degraded open-cathode PEM fuel cell stack

The well-known challenges to overcome in PEM fuel cell research are their relatively low durability and the high costs for the platinum catalysts. This work focuses on degradation mechanisms that are present in open-cathode PEM fuel cell systems and their links to the decaying fuel cell performance. Therefore a degraded, open-cathode, 20 cell, PEM fuel cell stack was analyzed by means of in-situ and ex-situ techniques. Voltage transients during external perturbations, such as changing temperature, humidity and stoichiometry show that degradation affects individual cells quite differently towards the end of life of the stack. Cells located close to the endplates of the stack show the biggest performance decay. Electrochemical impedance spectroscopy (EIS) data present non-reversible catalyst layer degradation but negligible membrane degradation of several cells. Post-mortem, ex-situ experiments, such as cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) show a significant active area loss of the first cells within the stack due to Pt dissolution, oxidation and agglomeration. Scanning electron microscope (SEM) images of the degraded cells in comparison with the normally working cells in the stack show severe carbon corrosion of the cathode catalyst layers.     

Consistent modeling of a single PEM fuel cell using Onsager's principle

In this paper a novel approach is proposed for a three-dimensional (3D) modeling of a High Temperature Exchange Membrane Fuel Cell (HTPEMFC). This new modeling is based on Onsager's principle of minimum energy dissipation that is applicable for near equilibrium and coupled irreversible systems. In particular, for low conductivity membranes, this leads to a one directional proton movement through the membrane. The resulting equations are numerically solved for a real single cell geometry, using a 3D finite volume discretization. Results are analyzed and validated against experimental data.     

Thermal modeling and temperature control of a PEM fuel cell system for forklift applications

Temperature changes in PEM fuel cell stacks are considerably higher during load variations and have a negative impact as they generate thermal stresses and stack degradation. Cell hydration is also of vital importance in fuel cells and it is strongly dependent on operating temperature. A combination of high temperature and reduced humidity increases the degradation rate. Stack thermal management and control are, thus, crucial issues in PEM fuel cell systems especially in automotive applications such as forklifts.     

MW cogenerated proton exchange membrane fuel cell combined heat and power system design for eco-neighborhoods in North China

Buildings account for most of the greenhouse gas (GHG) emissions causing global warming. The development of eco-neighborhood can improve the energy efficiency of buildings and reduce GHG emissions. A combined heat and power (CHP) system based on proton exchange membrane fuel cells (PEMFCs) is designed to supply electricity and thermal for eco-neighborhood in North China with low GHG emissions. Effects of different inlet parameters, such as PEMFC inlet pressure and current density, on multi-stack CHP system performance are discussed. Coupled with a dynamic load scenario, the adaptability of the designed PEMFC-CHP system is studied through PI control with an electricity-led strategy and a thermal-led strategy. Both strategies can effectively reduce GHG emissions and the eco-neighborhood with PEMFC-CHP system is more environmental friendly compared to conventional energy supply. The electricity-led strategy can satisfy the energy consumption of the eco-neighborhood but with thermal waste. The energy consumption for most of the time during a year can be satisfied by the PEMFC-CHP system under the thermal-led strategy, but the electricity gap exists as the thermal demand is lower. Under the electricity-led strategy, the GHG emission reduction of the eco-neighborhood under electricity-led strategy and thermal-led strategy are around 7000 ton and 5000 ton per year, respectively.     

Modeling and control of a PEM fuel cell based hybrid multilevel inverter

Multilevel inverter is an effective and practical solution for increasing power demand and reducing harmonics of AC waveforms. It is mainly employed in the distributed energy sources area because several batteries, fuel cell and solar cell can be connected through multilevel inverter to feed a load. This paper investigates the potentials of a single-phase Hybrid Cascaded Multilevel Inverter (HCMLI) fed from Proton Exchange Membrane Fuel Cell (PEMFC). A mathematical model of the PEMFC supplying HCMLI has been developed. This paper also presents the effect of a novel hybrid modulation on the device switching losses and harmonics of HCMLI. The proposed hybrid modulation technique combines the fundamental frequency switching scheme and Variable Frequency Inverted Sine Pulse Width Modulation (VFISPWM) technique. A comparison between the hybrid modulation strategy and the conventional Phase Disposition (PD) PWM method is also presented in terms of THD and switching losses. A suitable PID controller has been designed to control the output voltage of fuel cell based HCMLI, so that it can provide constant AC voltage with minimum THD up to the rated conditions. The inverter circuit topology and its control scheme are described in detail and their performance is verified based on simulation and experimental results.