Maximum equivalent efficiency and power output of a PEM fuel cell/refrigeration cycle hybrid system

With the help of the current models of proton exchange membrane (PEM) fuel cells and three-heat-source refrigeration cycles, the general model of a PEM fuel cell/refrigeration cycle hybrid system is originally established, so that the waste heat produced in the PEM fuel cell may be availably utilized. Based on the theory of electrochemistry and non-equilibrium thermodynamics, expressions for the efficiency and power output of the PEM fuel cell, the coefficient of performance and cooling rate of the refrigeration cycle, and the equivalent efficiency and power output of the hybrid system are derived. The curves of the equivalent efficiency and power output of the hybrid system varying with the electric current density and the equivalent power output versus efficiency curves are represented through numerical calculation. The general performance characteristics of the hybrid system are discussed. The optimal operation regions of some parameters in the hybrid system are determined. The advantages of the hybrid system are revealed.     

The parametric optimum analysis of a proton exchange membrane (PEM) fuel cell and its load matching

Based on the irreversible model of a PEM fuel cell working at steady state, expressions for the power output, efficiency and entropy production rate of the PEM fuel cell are analytically derived by using the theory of electrochemistry and non-equilibrium thermodynamics. The effects of multi-irreversibilities resulting from electrochemical reaction, heat transfer and electrical resistance on the key parameters of the PEM fuel cell are analyzed. The curves of the power output, efficiency and entropy production rate of the PEM fuel cell varying with the electric current density are represented through numerical calculation. The general performance characteristics of the PEM fuel cell are revealed and the optimum criteria of the main performance parameters are determined. Moreover, the optimal matching condition of the load resistance is obtained from the relations between the load resistance and the power output and efficiency. The effects of the leakage resistance on the performance of the PEM fuel cell are expounded and the optimally operating states of the PEM fuel cell are further discussed.     

Performance analysis and parametric optimum criteria of a class of irreversible fuel cell/heat engine hybrid systems

Based on the current models of solid oxide fuel cells and two-heat-source heat engines consisting of two isothermal and two polytropic processes, a general model of a class of fuel cell/heat engine hybrid systems is established, in which multi-irreversibilities existing in real hybrid systems are taken into account. Expressions for the efficiency and power output of the hybrid systems are analytically derived from the model. The curves of the efficiency and power output of the hybrid systems varying with the current density and the efficiency versus power output curves are represented through numerical calculation. The general performance characteristics of the hybrid systems are revealed and the optimum criteria of the main performance parameters are determined. The effects of some key irreversibilities existing in the fuel cell, regenerator and two-heat-source heat engine on the performance of the hybrid systems are discussed in detail. The results obtained here are very general and may be directly used to derive the various interesting conclusions of the hybrid systems which are operated under different special cases.     

Commercial vehicle auxiliary loads powered by PEM fuel cell

The commercial vehicles are in leadership in emission production for on-road vehicles. This high rate of emission is released in highly populated areas where diesel driven internal combustion engines are running in inefficient operating ranges. Except the propulsion, the internal combustion engine is powering the auxiliary devices such as refrigerator unit, etc. The auxiliary units are significant contributor to the overall pollutant production. In this paper the auxiliary load power supply for refrigerator unit is shifted from internal combustion engine to PEM fuel cell. The decrease in CO₂ accumulated emissions was estimated by simulation model containing vehicle model (tire, brake, differential, gearbox and driver model), diesel engine model and auxiliary power demand model. Four stroke diesel engine was modeled and investigated. For this investigation the fully filled truck was used for simulating 100% weight load. The gross weight is 7500 kg.The novelty of the approach is the simulation performed on realistic combination of city and urban road cycle. The focus was on modelling the realistic truck driving cycle in order to correctly predict emission and fuel consumption reduction. Since initial investigation are performed on constant load demand of fuel cell, simplified model of PEMFC was applied. PEM fuel cell stack was designed in order to meet the demands of auxiliary consumers. The H₂ consumption and size of hydrogen tank was estimated based on assumed 8-h daily drive. Finally, the migration of power supply for auxiliary units on commercial vehicle from internal combustion engine showed potential of fuel savings and CO₂ reduction of up to 9% for a given case on this specific test cycle.     

Fast start-up of a diesel fuel processor for PEM fuel cells

Fuel cell systems based on liquid fuels are particularly suitable for auxiliary power generation due to the high energy density of the fuel and its easy storage. Together with industrial partners, Oel-Waerme-Institut is developing a 3 kW_el PEM fuel cell system based on diesel steam reforming to be applied as an APU for caravans and yachts. The start-up time of a fuel cell APU is of crucial importance since a buffer battery has to supply electric power until the system is ready to take over. Therefore, the start-up time directly affects the battery capacity and consequently the system size, weight, and cost.     

Operating line analysis of fuel processors for PEM fuel cell systems

At least three different definitions of fuel processor efficiency are in widespread use in the fuel cell industry. In some instances the different definitions are qualitatively the same and differ only in their quantitative values. However, in certain limiting cases, the different efficiency definitions exhibit qualitatively different trends as system parameters are varied. In one limiting case that will be presented, the use of the wrong efficiency definition can lead a process engineer to believe that a theoretical maximum in fuel processor efficiency exists at a particular operating condition, when in fact no such efficiency optimum exists. For these reasons, the objectives of this paper are to: (1) quantitatively compare and contrast these different definitions, (2) highlight the advantages and disadvantages of each definition and (3) recommend the correct definition of fuel processor efficiency.     

Energy efficiency analysis of an integrated glycerin processor for PEM fuel cells: Comparison with an ethanol-based system

The aim of this work is to analyze energetically the use of glycerin as the primary hydrogen source to operate a proton exchange membrane fuel cell. A glycerin processor system based on its steam reforming is described departing from a previous process model developed for ethanol processing. Since about 10% w/w of glycerin is produced as a byproduct when vegetable oils are converted into biodiesel, and due to the later is increasing its production abruptly, a large glycerin excess is expected to oversaturate the market. The reformed stream contains mainly H₂ but also CO, CO₂, H₂O and CH₄. As CO is a poison for PEM fuel cell type, a stream purification step is previously required. The purification subsystem consists of two water gas shift reactors and a CO preferential oxidation reactor to reduce the CO levels below 10 ppm. The reforming process is governed by endothermic reactions, requiring thus energy to proceed. Depending on the system operation point, the energy requirements can be fulfilled by burning an extra glycerin amount (to be determined), which is the minimal that meets the energy requirements. In addition a self-sufficient operation region can be distinguished. In this context, the water/glycerin molar ratio, the glycerin steam reformer temperature, the system pressure, and the extra glycerin amount to be burned (if necessary) are the main decision variables subject to analysis. Process variables are calculated simultaneously, updating the composite curves at each iteration to obtain the best possible energy integration of the process. The highest net system efficiency value computed is 38.56% based on the lower heating value, and 34.71% based on the higher heating value. These efficiency values correspond to a pressure of 2 atm, a water/glycerin molar ratio of 5, a glycerin steam reformer temperature of 953 K, and an extra glycerin amount burned of 0.27 mol h⁻¹. Based on the main process variables, suitable system operation zones are identified. As in practice, most PEM fuel cells operate at 3 atm, optimal variable values obtained at this condition are also reported. Finally, some results and aspects on the system performance of both glycerin and ethanol processors operated at 3 atm are compared and discussed.     

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.     

Methanol fuel processor and PEM fuel cell modeling for mobile application

The use of hydrocarbon fed fuel cell systems including a fuel processor can be an entry market for this emerging technology avoiding the problem of hydrogen infrastructure. This article presents a 1 kW low temperature PEM fuel cell system with fuel processor, the system is fueled by a mixture of methanol and water that is converted into hydrogen rich gas using a steam reformer. A complete system model including a fluidic fuel processor model containing evaporation, steam reformer, hydrogen filter, combustion, as well as a multi-domain fuel cell model is introduced. Experiments are performed with an IDATECH FCS1200™ fuel cell system. The results of modeling and experimentation show good results, namely with regard to fuel cell current and voltage as well as hydrogen production and pressure. The system is auto sufficient and shows an efficiency of 25.12%. The presented work is a step towards a complete system model, needed to develop a well adapted system control assuring optimized system efficiency.     

Technological aspects of an auxiliary power unit with internal reforming methanol fuel cell

Increasing source runtime, speeding up the transient response, while minimizing weight, volume and cost of the power supply system are key requirements for portable, mobile and off-grid applications of fuel cells. In this respect, Internal Reforming Methanol Fuel Cell (IRMFC) modules were designed, constructed and tested based on an innovative double reformer (DRef) configuration and metallic bipolar plates (BPPs) with unique arrangement. Recently developed cross-linked Advent TPS^® high-temperature membrane electrode assemblies (MEAs) were employed for fuel cell operation at 210 °C. Taking into account the requirement for a light-weight and low-volume stack, Cu-based methanol reforming catalyst were supported on carbon papers, resulting in ultra-thin reformers. The proposed configuration offered a significant decrease in the weight and volume of the whole power system, as compared with previous voluminous foam-based modules. Moreover, specifically designed bipolar plates were made of coated Al-metal alloys, which proved to be stable in the strong acidic environment at elevated temperatures. The prototype 32MEAs-32DRef IRMFC stack of 100 W including home-made insulation casing, was integrated for operation at 200–210 °C and at 0.2 A cm⁻², demonstrating the functionality of the unit. A power output of 100.7 W (3.14 W per cell; 0.114 W cm⁻²) was achieved in the last run following several on-off cycles. The volumetric power density of the IRMFC stack including insulation and casing is around 30 W per lt, being among the highest reported either in the case of portable or stationary applications. Overall, the observed stability of reformers and bipolar plates was satisfactory within the timeframe of the work undertaken. Specific targets for improvement of the efficiency were identified, and the main drawback had to do with low thermal and mechanical stability of the membranes under start-up/shut-down transient operation.     

An improved TLBO with elite strategy for parameters identification of PEM fuel cell and solar cell models

Clean and renewable energy generation and supply has drawn much attention worldwide in recent years, the proton exchange membrane (PEM) fuel cells and solar cells are among the most popular technologies. Accurately modeling the PEM fuel cells as well as solar cells is critical in their applications, and this involves the identification and optimization of model parameters. This is however challenging due to the highly nonlinear and complex nature of the models. In particular for PEM fuel cells, the model has to be optimized under different operation conditions, thus making the solution space extremely complex. In this paper, an improved and simplified teaching-learning based optimization algorithm (STLBO) is proposed to identify and optimize parameters for these two types of cell models. This is achieved by introducing an elite strategy to improve the quality of population and a local search is employed to further enhance the performance of the global best solution. To improve the diversity of the local search a chaotic map is also introduced. Compared with the basic TLBO, the structure of the proposed algorithm is much simplified and the searching ability is significantly enhanced. The performance of the proposed STLBO is firstly tested and verified on two low dimension decomposable problems and twelve large scale benchmark functions, then on the parameter identification of PEM fuel cell as well as solar cell models. Intensive experimental simulations show that the proposed STLBO exhibits excellent performance in terms of the accuracy and speed, in comparison with those reported in the literature.     

Stabilised control strategy for PEM fuel cell and supercapacitor propulsion system for a city bus

Fuel Cell (FC) buses have been developed as a long term zero emission solution for city transportation and have reached levels of maturity to supplement the coming London 2020 Ultra low emission zone implementation. This research developed a scaled laboratory Fuel Cell/Supercapacitor hybrid drivetrain implementing DC/DC converters to maintain the common busbar voltage and control the balance of power. A novel and simple hybrid control strategy based on balancing the currents on the common busbar whilst maintaining a stable FC output has been developed. It has been demonstrated that the FC power output can be controlled at a user defined value for both steady state and transient load conditions. The proposed control strategy holds the promise of extending FC life, downsizing power systems and improving the FC operating efficiency.     

Design of a PEM fuel cell system for residential application

Fuel cells are energy transformation technologies and they are clean, don't damage to environment, have high efficiency and provide uninterruptible energy generation. Research and development studies about fuel cells have been done increasingly. In the recent years, fuel cell technologies have performed in some sectors such as military, industrial, space, portable, residential, transportation and trading.     

Sulfonation of PEEK-WC polymer via chloro-sulfonic acid for potential PEM fuel cell applications

The preparation and characterization of thin dense sulfonated poly-ether-ether-ketone with cardo group (PEEK-WC) membranes for proton exchange membrane fuel cell (PEMFC) applications are described. The sulfonation of PEEK-WC polymer was realized via chloro-sulfonic acid and different kinds of membrane samples were prepared with a sulfonation degree ranging from 67 to 99%. The degree of sulfonation, homogeneity and thickness significantly affect both the membrane transport properties and the electrochemical performances. The dense character of the membranes was confirmed by SEM analysis. Proton conductivity measurements were carried out in a temperature range from 30 to 80 °C and at 100% of relative humidity, reaching 5.40×10⁻³ S/cm⁻¹ as best value at 80 °C and with a sulfonation degree (DS) of 99%. At the same conditions, a water uptake of 17% was achieved. DSC and TGA characterizations were used in order to determine the thermal stability of the membranes, confirming a T_g ranging between 206 and 216 °C depending on the DS, whereas FT-IR yielded indication about intermolecular interactions and water uptake at various sulfonation degrees.     

Water balance for the design of a PEM fuel cell system

The design of a proton exchange membrane (PEM) fuel cell system is important for the optimization of the function of supporting parameters in the fuel cell. The water balance in a PEM fuel cell is investigated based on the water transport phenomena. In this investigation, the diffusion of water from the cathode side to the anode side of the cell is observed to not occur at 20% relative humidity at the cathode (RHC) and 58% relative humidity at the anode (RHA). The minimum concentration of condensed water at the cathode side is observed at a cathode gas inlet relative humidity of 40% RHC–92% RHC and at temperatures between 343 K and 363 K. RHC operating conditions that are greater than 90% and at a temperature of 363 K increased the concentration of condensed water and occurred quickly, which result in a water balance that became difficult to control. On the anode side, the condensation of water is observed at operating temperatures of 353 K and 363 K.     

Exergy analysis of a regional-distributed PEM fuel cell system

In this paper, the exergy flow and exergy efficiency of a 3 kW proton-exchange-membrane fuel cell were investigated, and the regional characteristic of the distributed energy system was considered. In the environmental temperature range of 263–313 K, the difference in the total efficiency of the proposed system was 6%. On the other hand, the difference in the exergy total efficiency of the same temperature range was 30%. Moreover, as a result of examining how to improve the exergy efficiency of this system, certain improvement methods were proposed: (a) preheat the city-gas and air supplied to the system using exhaust heat and raise the combustion temperature; (b) preheat the water supplied to the system using exhaust heat; (c) change the catalyst material of each unit and reduce the amount of cooling of the reformed gas; and (d) examine the combined cycle power generation. The exergy efficiency, in the case of introducing the proposed system into individual homes in Sapporo, Tokyo, and Kagoshima, was evaluated. Consequently, when the system was introduced into a community with low outside air temperatures, exergy efficiency increased compared with communities with high outside air temperatures.     

Parametric sensitivity analysis of PEM fuel cell electrochemical Model

In order to obtain an adequate PEM Fuel Cell model, it is necessary to define the values for a specific group of modeling parameters. The disagreements between the experimental and simulation results arise because of uncertainties stemming not only from the experimental measurements, but also from the modeling parameters used in the theoretical calculations. The modeling parameters were analyzed using Multi-Parametric Sensitivity Analysis (MPSA). This paper presents a sensitivity investigation of PEMFC electrochemical models and aims to determine the relative importance of each parameter on the modeling results. A computer program is written in Dev-cpp environment to calculate the sensitivity index for each parameter. As a result, the parameters were classified according to their influence in the modeling results as: insensitive, sensitive and highly sensitive. Thus it is possible to evaluate the relative importance of each parameter to the simulation accuracy. The present work benefits to understand the most effecting parameters, thus it helps the manufacturer to be more cautious in defining the exact value for them.     

PEM fuel cell air-feed system observer design for automotive applications: An adaptive numerical differentiation approach

In this paper, an adaptive algebraic observer is proposed for a Polymer Electrolyte Membrane Fuel Cell (PEMFC) air-feed system, based on Higher Order Sliding Mode (HOSM) differentiators. The goal is to estimate oxygen and nitrogen partial pressures in the fuel cell cathode side, using measurements of supply manifold pressure and compressor mass flow rate. As the proposed technique requires the time derivatives of the states, Lyapunov-based adaptive HOSM differentiators are synthesized and implemented for estimating these derivatives without a-priori knowledge of the upper bounds of their higher order time derivatives. The performance of the proposed method is validated through experiments on a Hardware-In-Loop (HIL) test bench. These results illustrate the feasibility and effectiveness of the proposed approach.     

Performance analysis of a new designed PEM fuel cell

In this paper, a new design for the flow channels is presented, and a parametric study of the proton exchange membrane (PEM) fuel cell is conducted in order to investigate the effect of the new flow channels, as well as different operating parameters, on the efficiency and energy output of the cell. Design parameters are selected based on studies presented in the literature to build a physical and practical model. With the new design of the flow channels, it is noticed that the cell efficiency increases from 33.8% to 47.7% if the temperature of the cell is increased. The power output of the cell increases from 2.6 to 282.5 W when the cell temperature and the current density are increased. Moreover, decrease in the efficiency of the cell ranges from 45.5% to 28.4% with the increase in the current density and membrane thickness. Based on the analytical model, design parameters were selected to manufacture a fuel cell that has a power output of 175 W and an efficiency of 35% running at 353 K and 3 bar, with an effective membrane area of 450 cm². Experiments are conducted to investigate the effect of newly designed flow channels on pressure distribution. It is found that when hydrogen is supplied from both inlets, pressure across the channels become symmetric and, therefore increasing the power output. This study reveals that, with the proper choice of design parameters, a PEM fuel cell is an attractive economical, efficient, and environmental solution when compared with conventional systems of power generation such as gas turbines. Copyright © 2011 John Wiley & Sons, Ltd.     

Maximum equivalent power output and performance optimization analysis of an alkaline fuel cell/heat-driven cycle hybrid system

A generic model of the hybrid system consisting of an alkaline fuel cell (AFC) and a heat-driven cycle, which may work as either a refrigerator or a heat pump, is originally established. On the basis of the models of AFCs and three-heat-reservoir cycles, the equivalent power output and efficiency of the hybrid system are obtained. The performance characteristic curves of the hybrid system are represented through numerical calculation. The maximum equivalent power output and efficiency of the hybrid system are determined. Problems concerning the optimal operation of the hybrid system are discussed. The effects of the main irreversible losses on the performance of the hybrid system are investigated in detail. It is important to note that the waste heat produced in the AFC can be readily used in such a hybrid cycle.