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The paper focuses on the experimental results of a series of tests performed on a hybrid electrical source. The hybrid generator is made up of a fuel cell primary source equipped with an ultracapacitor storage device. The paper presents an examination of the steady-state and transient performance of the hybrid fuel cell-ultracapacitor source in terms of power quality. The aim is to investigate on fuel cell-ultracapacitor source’s behavior to feed pulsing loads.

A dynamic simulation of a PEMFC hybrid system has been developed in a MATLAB/SIMULINK environment to study the component interactions between a diesel fuel processor, a PEMFC system, a compressor/expander system, and a battery pack. Each subsystem has been modeled using its fundamental reactions or processes. The simulation also allows subsystem performance to be analyzed and control strategies to be developed and tested for a range of configurations. This paper describes the models used in the dynamic simulation tool and how these models are programmed and implemented in the MATLAB/SIMULINK environment. The paper also presents the results from a study of a PEMFC marine system as an auxiliary power source for a ship hotel load to illustrate the capability of the simulation tool. The analysis focuses on the effect of using a 1.5 MWe fuel cell stack and a diesel fuel processor with 36 tonnes of high-temperature LAIS (lithium-aluminium/iron sulphide) battery pack (2.88 MWh) on the performance of the system under the hotel load duty cycle. A steady-state analysis was performed for the average system power of 1.5 MWe, and the results of steady state calculations are also presented.

The purpose of this paper is to present a nonlinear control method for accurately maintaining coolant temperature within a proton exchange membrane (PEM) fuel cell stack by controlling coolant flow rate. Due to the current sensitive nature of the membrane and a strict relative humidity requirement it is critical to precisely control the internal temperature of the fuel cell. First, an optimization-based parameter identification is applied to determine unknown coefficients to the nonlinear thermal model of the fuel cell stack. The stack is modeled according to a lumped parameter continuous-flow stirred tank reactor (CSTR) form. The paper then presents a nonlinear disturbance rejection control technique to accomplish the necessary temperature control. Experimental data from a 17-cell fuel cell stack is used for both the modeling and the control portions of this work.

This paper presents a technical and economical study of a hybrid—fuel cell, photovoltaic, and battery—electric generation system. The system is installed on five different remote sites. These sites are family houses located in different regions in France beyond the reach of electrical power lines. The optimum system configuration is not often easily found and a lot of calculations and/or simulations are required in order to decide which combination gives the best technical and financial benefit. The aim of this study is to design each component of the remote generation system in order to get the best technical and financial combination. In this paper, a method is suggested to find the optimum combination for a hybrid power system dedicated to off-grid electricity users. Indeed, this project permits to save up to 25&percent; of the initial cost.

This paper presents the bubble transport phenomenon at the anode of a micro-direct methanol fuel cell (μDMFC) from a mesoscopic viewpoint. Carbon dioxide bubbles generated at the anode may block part of the catalyst/diffusion layer and also the flow channels that cause the μDMFC malfunction. Lattice-Boltzmann simulations were performed in this paper to simulate the two-phase flow in a microchannel with an orifice which emulates the bubble dynamics in a simplified porous diffusion layer and in the flow channel. A two-dimensional, nine-velocity model was established. The buoyancy force, the liquid-gas surface tension, and the fluid-solid wall interaction force were considered and they were treated as source terms in the momentum equation. Simulation results and parametric studies show that the pore size, the fluid stream flow rate, the bubble surface tension, and the hydrophilic effect between the fluid and the solid wall play the major roles in the bubble dynamics. Larger pore size, higher methanol stream flow rate, and greater hydrophilicity are preferred for bubble removal at the anode diffusion layer and also the flow channels of the μDMFC.

The fuel cell system and fuel cell gas turbine hybrid system represent an emerging technology for power generation because of its higher energy conversion efficiency, extremely low environmental pollution, and potential use of some renewable energy sources as fuels. Depending upon the type and size of applications, from domestic heating to industrial cogeneration, there are different types of fuel cell technologies to be employed. The fuel cells considered in this paper are mainly the molten carbonate (MCFC) and the solid oxide (SOFC) fuel cells, while a brief overview is provided about the proton exchange membrane (PEMFC). In all these systems, heat exchangers play an important and critical role in the thermal management of the fuel cell itself and the boundary components, such as the fuel reformer (when methane or natural gas is used), the air preheating, and the fuel cell cooling. In this paper, the impact of heat exchangers on the performance of SOFC, MCFC gas turbine hybrid systems and PEMFC systems is investigated. Several options in terms of cycle layout and heat exchanger technology are discussed from the on-design, off-design and control perspectives. A general overview of the main issues related to heat exchangers performance, cost and durability is presented and the most promising configurations identified.

A thermodynamic model for a gas turbine-fuel cell hybrid is created and described in the paper. The effects of gas turbine design parameters such as compressor pressure ratio, compressor efficiency, turbine efficiency, and mass flow are considered. The model allows to simulate the effects of fuel cell design parameters such as operating temperature, pressure, fuel utilization, and current density on the cycle efficiency. This paper discusses, based on a parametric study, optimum design parameters for a hybrid gas turbine. Because it is desirable to use existing gas turbine designs for the hybrids, the requirements for this hybridization are considered. Based on performance data for a typical 1600hp industrial single shaft gas turbine, a model to predict the off-design performance is developed. In the paper, two complementary studies are performed: The first study attempts to determine the range of cycle parameters that will lead to a reasonable cycle efficiency. Next, an existing gas turbine, that fits into the previously established range of parameters, will be studied in more detail. Conclusions from this paper include the feasibility of using existing gas turbine designs for the proposed cycle.

This paper presents a review of the current situation in the computational fluid dynamics (CFD) modeling of fuel cells and highlights the significant challenges that lie ahead in the development of a comprehensive CFD model for fuel cell applications. The paper focuses on the issues concerned with solid oxide fuel cells and proton exchange membrane fuel cells because these are the two most poplar and probably the most promising types of fuel cells for both stationary and transport applications. However, the general principles presented in this paper are applicable to all types of fuel cells.

This paper conducts a multiscale parametric study of temperature and composition effects on the transport phenomenon of a solid oxide fuel cell (SOFC). The molecular dynamics technique was employed to study the transport phenomenon of the solid electrolyte, which is made of yttria-stabilized zirconia. The influences of Y2O3 concentration and various operation temperatures on the SOFC were studied. Simulation results show that there exists an optimal concentration of 8mol% of Y2O3 in the composition for oxygen transport. Also higher operation temperature promotes the oxygen ion-hopping process that increases the ionic conductivity. A macroscale parametric study was also conducted in this paper to validate the influence of the temperature uniformity in the solid electrolyte by employing the computational fluid dynamics technique. The temperature distribution maps of a single-cell planar SOFC with coflow, counterflow and cross-flow channel designs are presented. The results conclude that the coflow configuration is the best design of the three.

A simple, low-cost testing method is proposed for fuel cell hardware development. A perforated aluminum foil with an array of small holes covered with carbon paper or cloth replaces the membrane electrode assemblies to test the contact resistance and gas permeability of the carbon paper. Practical fuel cells of 50cm2 reaction area with different gasket thicknesses and compressed pressures are tested for performance. The results of ohmic resistance and permeability of compressed carbon paper indicate strong relevance to cell performance, demonstrating that this novel testing method is valuable for fuel cell hardware development. Also, the compression mechanism of the diffusion layer is discussed along with a proposal for a strategy for improving cell performance. After that, an advanced design of a 25cm2 single cell is developed. The results of cell performance of the advanced cell are acceptable and competitive with the performance data of commercial products.

The intention of this paper is to present the dynamic models for the molten carbonate fuel cell (MCFC)-gas turbine hybrid cycle. This paper analyzes the performance of various components in the hybrid power plant, such as the compressor, turbine, recuperator, generator, fuel cell stack, etc. The modular simulation models of these components are presented. Based on the dynamic simulation modeling principle, one bottoming hybrid MCFC-microturbine cycle was studied to carry out the simulation. The simulation result can reflect the dynamic response of the hybrid power plant.

Uniform gas flow distribution in a fuel cell system is desired to attain maximum power operation potential. Two types of manifold systems are often used in fuel cell stacks; they are internal manifold system and external manifold system. This paper presents the modeling approach using the Computational Fluid Dynamics (CFD) method in analyzing fluid flow and heat transfer for the external manifold fuel cell stacks and stack module design. Computational models based on a Megawatt carbonate fuel cell stack module have been developed for investigating the fuel and oxidant flow distributions through the external manifold systems. This paper presents the modeling approaches and flow and temperature distribution results for externally manifolded fuel cell stack and stack module.

Due to constantly increasing electricity consumption, networks are becoming overloaded and unstable. Decentralization of power generation using small-scale local cogeneration plants becomes an interesting option to improve economy and energy reliability of buildings in terms of both electricity and heat. It is expected that stationary applications in buildings will be one of the most important fields for fuel cell systems. In northern countries, like Finland, efficient utilization of heat from fuel cells is feasible. Even though the development of some fuel cell systems has already progressed to a field trial stage, relatively little is known about the interaction of fuel cells with building energy systems during a dynamic operation. This issue could be addressed using simulation techniques, but there has been a lack of adequate simulation models. International cooperation under IEA/ECBCS/Annex 42 aims at filling this gap, and the study presented in this paper is part of this effort. Our objective was to provide the means for studying the interaction between a building and a fuel cell system by incorporating a realistic fuel cell model into a building energy simulation. A two-part model for a solid-oxide fuel cell system has been developed. One part is a simplified model of the fuel cell itself. The other part is a system level model, in which a control volume boundary is assumed around a fuel cell power module and the interior of it is regarded as a “black box.” The system level model has been developed based on a specification defined within Annex 42. The cell model (programed in a spreadsheet) provides a link between inputs and outputs of the black box in the system model. This approach allows easy modifications whenever needed. The system level model has been incorporated into the building simulation tool IDA-ICE (Indoor Climate and Energy) using the neutral model format language. The first phase of model implementation has been completed. In the next phase, model validation will continue. The final goal is to create a comprehensive but flexible model, which could serve as a reliable tool to simulate the operation of different fuel cell systems in different buildings.

In this paper, a three-dimensional finite volume model of a molten carbonate fuel cell (MCFC) is presented. The model applies a detailed electrochemical and thermal analysis to a planar MCFC stack of given geometry and assigned input flows conditions, material properties and assigned external heat losses, calculating global energy balances and reactant utilization, as well as internal temperature and chemical composition profiles, pressure profiles, polarization losses, and current density and voltage distribution over the stack. The model is calibrated on the available data for an experimented MCFC stack manufactured by Ansaldo Fuel Cells. The comparison of 2D versus 3D simulations is first discussed, showing the importance of the 3D model for an accurate analysis of real stack operation under significant heat loss conditions, but also showing the mutual influence of heat transfer between adjoining cells and evidencing the variable electrical performances between different cells of the same stack. As a counterpart, application of the 2D model, which takes advantage by much shorter calculation time while keeping a reasonable accuracy in the overall energy balances, is anyway indicated for complex cycle analysis and cycle optimization, where a complete 3D stack analysis may be limited to selected cases. Then, the model is applied to the off-design analysis of hybrid cycles based on a recuperated gas turbine arrangement where variable pressure ratios and fuel supply conditions are assumed for the fuel cell. The effects of the operating pressure and of the adoption of different fuel compositions are considered, with a cycle layout that may include natural gas reforming or is directly fed by a syngas provided by an external source, simulating different fuel feedstocks (e.g., coal gasification). Complete results are presented, in terms of fuel cell and overall cycle performances.

This paper studies the transport phenomena inside the electrolyte of proton exchange membrane fuel cells (PEMFCs) using atomistic simulation techniques. The investigated material of the electrolyte is Nafion®, which is the most widely adapted polymer membrane in low-temperature fuel cells. The molecular dynamics simulation system includes part of the Nafion structure, numerous water molecules, and the transporting cations. The cations are assumed to be hydroxoniums (H3O+), which are a hydrogen proton combined with a water molecule. Simulation results indicated that the electrostatic energy dominated the other potential energies in the total internal energy analysis. Clusters of water molecules tend to move toward the sulfonic acid group in the Nafion fragment, where the hydrophilic/hydrophobic characteristics can be observed. The transport phenomena of hydroxoniums are classified into two categories—continuous migration and noncontinuous hopping. The self-diffusion coefficients of the hydroxoniums and the water molecules in the membrane were evaluated to be 3.476×10−5 cm2/s and 4.993×10−5 cm2/s respectively, based on the Einstein relation. The calculated self-diffusion coefficients are of the same order of magnitude as the experimental results, which indicates this atomistic simulation is reaching more and more practical in engineering analysis.

An advanced stage has been reached in the research and development of alternative vehicle propulsion systems, aiming at assuring acceptable levels of both consumption and emissions. Many different criteria, often expressed in incommensurable units, such as weight, reliability or availability, cost, etc., must be taken into account in order to obtain an “optimal” design for such systems. The design of such vehicles is the result of a complex synthesis, requiring high degree of methodologies involving tradeoffs among multiple criteria. This paper proposes a probabilistic multicriteria decision analysis applied to the design of a hybrid electric vehicle. In particular, a Bayesian estimation approach is proposed and numerically illustrated, with the purpose of determining the optimal decision for the systems’ design under uncertainty. In the course of the numerical application, it is shown how such methodology is able to integrate and update available information, even if poor and uncertain, on the basis of new experimental data.

Natural gas appears to be a fuel of great interest for solid oxide fuel cell (SOFC) systems. It mainly consists of methane, which can be converted into hydrogen by direct internal reforming (DIR) within the SOFC anode. However, a major limitation to DIR is carbon formation within the ceramic layers at intermediate temperatures. This paper proposes a model solution using the CFD-ACE software package to simulate the behavior of a tubular SOFC. A detailed thermodynamic analysis is carried out to predict the boundary of carbon formation for SOFCs fueled by methane. Thermodynamic equilibrium calculations that take into account Boudouard and methane cracking reactions allow us to investigate the occurrence of carbon formation. This possibility is discussed from the values of driving forces for carbon deposition defined as α=PCO2/(KBPCO2) and β=PH22/(KCPCH4), from the equilibrium constants KB and KC of the Boudouard and cracking reactions, and from the partial pressure Pi of species i. Simulations allow the calculation of the distributions of partial pressures for all the gas species (CH4, H2, CO, CO2, and H2O), current densities, and potentials of both electronic and ionic phases within the anode part (i.e., gas channel and Cermet anode). Finally, a mapping of α and β values enables us to predict the predominant zones where carbon formation is favorable (α or β<1) or unfavorable (α or β>1) according to the calculation based on thermodynamic equilibrium. With regard to the values of these different coefficients, we can say that a carbon formation can be supposed for temperature less than 800°C and for ratios xH2O/xCH4 smaller than 1.

A theoretical evaluation of the ohmic resistance of solid oxide fuel cells (SOFCs) is very important because internal ohmic resistances account for a large part of the losses occurring in SOFCs and significantly affect cell performance. However, in the majority of cases, a detailed evaluation of ohmic losses is not an elementary task, since the structure of the geometry makes it difficult to apply simple laws, such as R=ρl/S. The solution of a PDE equation is required, which has to be performed numerically. In this paper, two different numerical approaches have been applied to the simulation of the internal ohmic resistances of basic SOFC units, and the results have been compared. In particular, the commercial mathematical software FEMLAB and MATLAB have been used to implement the different numerical approaches. The agreement between the obtained results is very good.

In the thin-film solid oxide fuel cell (SOFC) concept of the German Aerospace Center (DLR) in Stuttgart, the entire membrane electrode assembly (MEA) is deposited onto a porous metallic substrate by an integrated multistep vacuum plasma spray (VPS) process. This concept enables the production of very thin and stable electrodes and electrolyte layers with a total cell thickness of only 100–120 μm. In this concept, the porous ferrite substrate material predominantly acts as mechanical cell support and as fuel gas distributor. In general, ferrite substrate alloys with high chromium and low manganese content show both excellent corrosion stability and adequate thermal expansion behavior. Nevertheless, at the high process temperature in the SOFC of ∼800°C, atomic transport processes can show a detrimental effect on cell performance, at least at the required long-term operation. Problems arise, in particular, through diffusion processes of Fe-, Cr-, and Ni-species between the Ni/8YSZ anode and the ferrite steel-based substrate material. This can induce significant structure changes both in the anode and the substrate. As a reliable solution of this key problem, a plasma sprayed thin diffusion barrier layer is seen at the interface between anode and substrate, which consists of an electrically conductive and chemically stable ceramic component. For this purpose, some doped perovskite-type LaCrO3, such as La1−xSrxCrO3−δ, La1−xCaxCrO3−δ, or La1−xSrxCr1−yCoyO3−δ were investigated and tested carefully at DLR. These types of perovskites show a high potential to fulfill all the required properties that are needed for the applicability as an anode-side diffusion barrier layer. The paper focuses on basic investigations of differently doped LaCrO3 compounds under SOFC-relevant conditions concerning thermal expansion, electrical conductivity, chemical stability, etc. Furthermore, first results of electrically and electrochemically characterized half cells carried out with some qualified doped LaCrO3 are shown. Finally, the diffusion barrier layer is demonstrated as a new SOFC component that is effective at cell operating conditions.

At the German Aerospace Center (DLR) in Stuttgart, a lightweight stack design for mobile applications was developed in cooperation with the automotive industry (BMW, Munich; Elring-Klinger, Dettingen; Rhodius, Weissenburg). This concept is based on the application of stamped metal sheet bipolar plates into which porous metallic substrate-supported cells (MSCs) are integrated. The paper concentrates on the one hand on the investigation of plasma sprayed button cells with a diameter of 48 mm on porous metallic substrates during reduction/oxidation and thermal cycling. On the other hand, another focus lies in the electrochemical testing of short stacks in the cassette arrangement. The microstructure of the cells was characterized by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction, and energy dispersive microanalysis (EDX) before and after operation. The cells and short stacks were electrochemically characterized mainly by long-term measurements (life cycle), by current-voltage measurements, and by impedance spectroscopy. In order to understand the nature of degradation mechanisms, the open-circuit voltages (OCV), the ohmic resistances, and the polarization resistances, during dynamic operation are compared and discussed. In order to distinguish between degradation effects due to the dynamic operation and usual stationary effects, these values are compared to values of noncycled cells. All of the cells investigated were able to withstand ten redox and ten thermal cycles without severe failure. Their redox- and thermal-cycling behavior are strongly dependent on their OCVs, which decrease during cycling. This proves that thermomechanical stresses in the electrolyte layer play a major role for the electrochemical performance of the cells during cycling. The improvement of the electrodes during the first 200 h of operation and the ohmic resistance of the cells are not significantly influenced by the cycling. The first four-cell short stack with the cassette arrangement shows promising results with an OCV of ∼4 V and an overall power of 92 W at 800°C. The performances of the single cells are in the range of 180–220 mW/cm2. The differences in cell performance can be attributed to different polarization resistances of the cells in the cassettes, which might be caused by a nonuniform gas supply in the short stack.

This paper analyzes and compares transient and steady-state performance characteristics of different types of single-shaft turbo-machinery for controlling the air through a pressurized solid oxide fuel cell (SOFC) stack that is integrated into a SOFC/GT pressurized hybrid system. Analyses are focused on the bottoming part of the cycle, where the gas turbine (GT) has the role of properly managing airflow to the SOFC stack for various loads and at different ambient conditions. Analyses were accomplished using two disparate computer programs, which each modeled a similar SOFC/GT cycle using identical generic gas turbine performance maps. The models are shown to provide consistent results, and they are used to assess: (1) the influence of SOFC exhaust composition on expander behavior for on-design conditions, (2) the off-design performance of the bypass, bleed, and variable speed controls for various part-load conditions and for different ambient conditions; (3) the features of such controls during abrupt transients such as load trip and bypass/bleed valve failure. The results show that a variable speed microturbine is the best option for off-design operation of a SOFC/GT hybrid system. For safety measures a bleed valve provides adequate control of the system during load trip. General specifications for a radial GT engine for integration with a 550 kW pressurized SOFC stack are identified, which allow operation under a wide range of ambient conditions as well as several different cycle configurations.

A high-precision method to measure efficiency of fuel cells with a 0.1&percent; margin of error is proposed. This method is principally divided into two procedures: determining the composition of fuel gas to be fed into a fuel cell system and measuring the flow rate of the fuel gas. The composition of the fuel gas is determined by an FTIR (Fourier transform infrared spectrometer) and/or a QMS (quadrapole mass spectrometer) with a built-in sonic nozzle sampling system. The flow rate was measured by the tracer gas method; that is, a given amount of tracer gas, such as one of the noble gases, was introduced into the line of the fuel gas, then, the mixed gas was sampled at the point where the tracer gas had been well mixed, and the concentration of the tracer gas was determined by the QMS. In this paper, a gravimetric calibration method using a highly sensitive balance is also proposed for flow control of the tracer gas. Also proposed are calibration of the FTIR and the QMS to establish the required low uncertainty or high accuracy of the measurement of the efficiency.

The use of proton exchange membrane fuel cells (PEFC) based power trains and stationary systems has been technically demonstrated but is still far from commercial application. Technical development is still required to reach cost and durability targets, and to this aim, modeling and simulation are useful tools to obtain both better understanding of the fundamental occurring processes and to shorten design-associated costs and time. In this paper, a hierarchical 3D-1D approach is proposed, to overcome the deficiencies of a full 1D approach and the characteristic computational costs of a full 3D approach. The polymeric membrane and catalyst layers are represented by a local 1D model, while channels, gas diffusion layers, and solid electrodes are modeled by a full 3D approach. The model capabilities are first investigated with respect to experimental data by means of a full fuel cell simulation; the main chemical, fluid dynamic, and thermal fields are then analyzed in a straight channel configuration. The proposed 3D/1D model is able to accurately represent PEFC specific phenomena and their physical coupling. It could be then successfully applied to both design and development.

This paper investigates the thermodynamic potential of the integration of molten carbon fuel cell (MCFC) technology with gas turbine systems for small-scale (sub-megawatt or sub-MW) as well as large-scale (multi-MW) hybrid cycles. Following the proposals of two important MCFC manufacturers, two plant layouts are discussed, the first based on a pressurized, externally reformed MCFC and a recuperated gas turbine cycle and the second based on an atmospheric MCFC, with internal reforming integrated within an externally fired gas turbine cycle. Different levels of components quality are considered, with an analysis of the effects of variable pressure ratios, different fuel mixture compositions (variable steam-to-carbon ratio) and turbine inlet temperature levels, together with potential advantages brought about by an intercooled compression process. The analysis shows interesting effects due to the peculiarity of the mutual interactions between gas turbine cycle and fuel cells, evidencing the importance of a careful thermodynamic optimization of such cycles. Results show the possibility to achieve a net electrical efficiency of about 57–58&percent; for a small plant size (with a difference of 1.5–2 percentage points between the two layouts), with the potential to reach a 65&percent; net electrical efficiency when integrated in advanced cycles featuring high-efficiency, large-scale equipment (multi-MW scale cycles).

Recently, small solid oxide fuel cell (SOFC) systems have been developed for various applications because of their high performance. In such small generation systems, quick and frequent start-stops are often required. However, it is generally considered that these start-stops with SOFC systems are not preferable because SOFC systems are operated at high temperature. Also, quantitative studies on the thermal behavior of small SOFC systems are limited. The purpose of this paper is to obtain insight into the possibility of using small SOFC systems with quick and frequent start-stops. A simple two-dimensional numerical model for 1 kW-class SOFC systems was fabricated to study this problem. The model consists of a cylindrical SOFC stack, a prereformer on the stack, a heat exchanger for exhaust gas, and a thermal insulator that covers the stack and the prereformer. Using this model, first, the characteristics of the power generation efficiency were estimated under various operating conditions. In addition, the validity of the modeling was verified. Next, the start-up dependence on their structure and operating conditions was investigated. Finally, for the cyclic daily start-up and shutdown (DSS) procedure, the total efficiency during a day was calculated when the energy loss during start-stops is considered. As a result of the analysis, the following points were found. First, the validity and accuracy of the modeling was established, and their efficiency under the rated condition becomes 60&percent; (DC/HHV) at a steam-carbon ratio=2.5 and an oxygen utilization=50&percent;. Next, the thickness of the thermal insulator (0.03 W/m/K) is required to be more than 6 cm to reduce the heat loss from the outer surface of the thermal insulator to <5&percent; of the provided fuel energy (2 kW) under the rated condition. In this case, it takes ca. 150 min to start, if the fuel (methane) flow rate is 3.02 NL/min, which is equivalent to 2 kW of heat flow. Finally, for the DSS operation, consisting of repetition of a 16 h operation and an 8 h stop in a day, the total efficiency decreases by ca. 1.5&percent; from the rated power generation efficiency. Therefore, it is clarified that 1 kW-class SOFC systems can be quite suitable even in the case where quick and frequent start-stops are required.

The paper focuses on the simulation of a hybrid vehicle with proton exchange membrane fuel cell as the main energy conversion system. A modeling structure has been developed to perform accurate analysis for powertrain and control system design. The models simulate the dynamics of the main powertrain elements and fuel cell system to give a sufficient description of the complex interaction between each component under real operating conditions. A control system based on a multilevel scheme has also been introduced and the complexity of control issues for hybrid powertrains have been discussed. This study has been performed to analyze the energy flows among powertrain components. The results highlight that optimizing these systems is not a trivial task and the use of precise models can improve the powertrain development process. Furthermore, the behavior of system state variables and the influence of control actions on fuel cell operation have also been analyzed. In particular, the effect of introducing a rate limiter on the stack power has been investigated, evidencing that a 2 kW/s rate limiter increased the system efficiency by 10&percent; while reducing the dynamic performance of the powertrain in terms of speed error.

This paper presents a two-dimensional model to describe the gas flow in an integrated reactor, developed at the CNR-ITAE Institute, and aimed to design a βeta5 kWe hydrogen generator, named HYGen II, to integrate with polymer electrolyte fuel cells (PEFCs) for residential applications. The model is able to simulate velocity profiles in order to investigate the reactor geometrical key parameters. The unit can convert light hydrocarbons (methane, propane, LPG, butane) into a hydrogen rich mixture. The processing unit consists of an innovative integrated dual bed reactor, filled with pellet catalysts: a proprietary Pt/CeO2 autothermal reforming (ATR) and a commercial intermediate temperature water gas shift (ITWS). For the last clean-up step, a single-stage preferential oxidation (PROX) process has been adopted. Moreover, an automation system to monitor operating conditions and control plant equipment has been designed.

Planar-solid-oxide-fuel-cell stacks (PSOFCSs), in PSOFC-based power-conditioning systems (PCSs), are subjected to electrical feedbacks due to the switching power electronics and the application loads. These feedbacks (including load transient, current ripple due to load power factor and inverter operation, and load harmonic distortion) affect the electrochemistry and the thermal properties of the planar cells thereby potentially deteriorating the performance and reliability of the cells. In this paper, a detailed study on the impact of these electrical effects on the performance of the PSFOC is conducted. To analyze the impact of such feedbacks, a spatiotemporal numerical system model is developed on a low-cost Simulink modeling platform and the model under transient and steady-state conditions is validated experimentally. Using this validated model, parametric analyses on the impacts of transience, power factor, and distortion of the application load as well as low-frequency current ripple is conducted. Finally, using experimental data, we demonstrate the long-term impact of two most significant electrical feedbacks on the area-specific resistance and the corresponding loss of effective stack power.

St. Andrews Fuel Cells Ltd. is a spin-off company (formed in February 2005) from the University of St. Andrews. The company’s focus is on the development of the SOFCRoll fuel cell. The SOFCRoll design is produced from tape casting and is fired in a single unit, offering reduced fuel cell production costs. Additionally, the self-supporting nature of the SOFCRoll geometry removes the need for thick cell components, further reducing cell cost and offering increased power densities. This paper reviews the development of the SOFCRoll concerning the processing and performance testing.

Large scale power production benefits from the high efficiency of gas-steam combined cycles. In the lower power range, fuel cells are a good candidate to combine with gas turbines. Such systems can achieve efficiencies exceeding 60&percent;. High-temperature solid oxide fuel cells (SOFC) offer good opportunities for this coupling. In this paper, a systematic method to select a design according to user specifications is presented. The most attractive configurations of this technology coupling are identified using a thermo-economic multi-objective optimization approach. The SOFC model includes detailed computation of losses of the electrodes and thermal management. The system is integrated using pinch based methods. A thermo-economic approach is then used to compute the integrated system performances, size, and cost. This allows to perform the optimization of the system with regard to two objectives: minimize the specific cost and maximize the efficiency. Optimization results prove the existence of designs with costs from 2400 $/kW for a 44&percent; efficiency to 6700 $/kW for a 70&percent; efficiency. Several design options are analyzed regarding, among others, fuel processing, pressure ratio, or turbine inlet temperature. The model of a pressurized SOFC–μGT hybrid cycle combines a state-of-the-art planar SOFC with a high-speed micro-gas turbine sustained by air bearings.

This paper presents a two-dimensional model to describe the gas flow in an integrated reactor, developed at the CNR-ITAE Institute, and aimed to design a βeta5kWe hydrogen generator, named HYGen II, to integrate with polymer electrolyte fuel cells (PEFCs) for residential applications. The model is able to simulate velocity profiles in order to investigate the reactor geometrical key parameters. The unit can convert light hydrocarbons (methane, propane, LPG, butane) into a hydrogen rich mixture. The processing unit consists of an innovative integrated dual bed reactor, filled with pellet catalysts: a proprietary Pt∕CeO2 autothermal reforming (ATR) and a commercial intermediate temperature water gas shift (ITWS). For the last clean-up step, a single-stage preferential oxidation (PROX) process has been adopted. Moreover, an automation system to monitor operating conditions and control plant equipment has been designed.

In the last years the development of fuel cell (FC) technology has highlighted the correlated problem of storage and transportation of gaseous fuels, particularly hydrogen and methane. In fact, forecasting a large scale application of the FC technology in the near future, the conventional technologies of storage and transportation of gaseous fuels will be inadequate to support an expectedly large request. Therefore, many studies are being devoted to the development of novel efficient technologies for gas storage and transport; one of those is methane and hydrogen storage in solid, water-based clathrate hydrates. Clathrate hydrates (CH) are nonstoichiometric, nanostructured complexes of small “guest” molecules enclosed into water cages, which typically form at relatively low temperature-high pressure. In nature, CH of natural gas represent an unconventional and unexploited energy source and methane hydrate technology is already applied industrially. More recently, striking literature reports showed a rapid approach to the possibility of obtaining hydrogen hydrates at room temperature/mild pressures. Methane hydrate formation has been shown to be heavily promoted by some chemicals, notably amphiphiles. Our research is aimed at understanding the basic phenomena underlying CH formation, with a goal to render hydrate formation conditions milder, and increase the concentration of gas within the CH. In the present paper, we show the results of a preliminary attempt to relate the structural features of several amphiphilic additives to the kinetic and thermodynamic parameters of methane hydrate formation—e.g., induction times, rate of formation, occupancy, etc. According to the present study, it is found that a reduction of induction time does not necessarily correlate to an increase of the formation rate and occupancy, and so on. This may be related to the nature of chemical moieties forming a particular amphiphile (e.g., the hydrophobic tail, head group, counterion, etc.). Moreover, a chemometric approach is presented which is aimed at obtaining information on the choice of coformers for H2 storage in hydrates at mild pressures and temperatures.

Prediction of mass transfer effects is a key element in fuel cell design. In this paper, the results of a generalized analysis appropriate to a wide range of designs and flow conditions are presented. Mass transfer in a rectangular gas passage, diffusion layer, and the combination of the two is considered. Fully developed viscous flow is presumed to occur within the passage, while the incompressible form of Darcy’s law is prescribed for the diffusion layer. The mathematical foundations for a simple mass transfer analysis are presented. Detailed calculations are then performed by means of a computational fluid dynamics code. These results are then correlated according to the analytical methodology in terms of nondimensional numbers appropriate to mass transfer analysis; namely, the overall mass transfer driving force as a function of the blowing parameter. Parametric studies are performed for a range of geometries, as characterized by the aspect ratio and blockage factor. It is shown that a simple solution for the overall driving force may readily be obtained from the two individual solutions for the conjugate mass transfer problem. This solution is quite general in its nature, and may readily be used to predict concentration polarization effects for a variety of fuel cells.

One of the main targets in the development of anode-supported solid oxide fuel cell (SOFCs) is to improve the electrochemical performance. This can be achieved by optimizing processing and microstructural parameters of the SOFCs. Variations of the thickness of the cathode functional layer and the cathode current collector layer, the grain size of the powders used for applying these layers, and the sintering temperature, can influence the electrochemical performance as such that lower operation temperatures become possible without detrimentally affecting the power output to a great extent. In this study the effect of variations of the sintering temperature of the cathode on (1) the microstructure, (2) the gas diffusivity and permeability in the cathode, and (3) electrochemical performance of FZJ-type anode-supported single cells, was investigated. The FZ-Ju¨lich cell design is based on anode-supported type cells, which are characterized by a relatively thick anode (thickness: 1.0–1.5 mm) consisting of a NiO/8YSZ cermet, a thin 8YSZ electrolyte, and a bi-layered cathode. The cathode distinguished two separated layers: first a cathode functional layer consisting of La0.65Sr0.3MnO3(LSM)/Y2O3-stabilized ZrO2 (8YSZ) and a cathode current collector layer of pure La0.65Sr0.3MnO3 (LSM). This study can be considered as a follow-up of that (Journal of Power Sources 141 (2005) 216–226) describing the improvement of the cell performance by a systematic variation of the microstructure. The experiments described in this paper and the corresponding results are part of a more extensive study to investigate in more detail the effect of the sintering temperature on the electrochemical performance of LSM-type SOFCs. Since research is still going on, conclusions, drawn in this contribution, are yet not definitive.

The combination of biomass gasification systems with fuel cells promises adequate systems for sustainable, decentralized energy conversion. Especially high temperature fuel cells are suited for this task because of their higher tolerance to impurities, their internal steam reforming potential, and favorable thermal integration possibilities. This paper presents the results of biosyngas utilization in solid oxide fuel cells with Ni/GDC anodes at 850 and 920°C. The relation between the fuel composition and the electrochemical performance is discussed, as well as the impact of sulfur up to a concentration of 9 ppmH2S. The investigations have made clear that Ni/GDC anodes can be operated within a wide range of biosyngas compositions. Sulfur has appeared to deactivate the anode for methane reforming. The oxidation of hydrogen and carbon monoxide are insensitive to sulfur, suggesting that both nickel and GDC are active electrocatalysts.

Proton exchange membrane (PEM) fuel cells show characteristics of high power density, low operating temperature, and fast start-up capability, which make them potentially suitable to replace conventional power sources (e.g., internal combustion engines) as auxiliary power units (APU) for on-board applications. This paper presents a methodology for a preliminary investigation on either sizing and operating management of the main components of an on-board power system composed by: (i) PEM fuel cell, (ii) hydrogen storage subsystem, (iii) battery, (iv) grid interface for the connection to an external electrical power source when available, and (v) electrical appliances and auxiliaries installed on the vehicle. A model able to reproduce the typical profiles of electric power requests of on-board appliances and auxiliaries has been implemented in a computer program. The proposed methodology helps also to define the sizing of the various system components and to identify the fuel cell operating sequence, on the basis of the above mentioned load profiles.

This paper presents the results of a system simulation study. The HYSYS 3.1 - ASPEN code has been used for simulation. The system consists of a fixed bed gasifier followed by reforming and clean-up units. The produced hydrogen gas is fed to a PEM fuel cell. The gasified hydrocarbons are hazelnut shells, bark, rice straw, animal waste, and two lignites. Hydrocarbon properties, gasification, and reforming process parameters all affect the system efficiency. The effect of the moisture content and oxygen to carbon ratio of the hydrocarbon feeds on the fuel processing and overall system efficiencies are presented. The overall efficiency of the system increases with increasing hydrocarbon feed oxygen to carbon ratio; this tendency is more evident at higher moisture levels.

This paper sets out the results of mathematical modeling and numerical simulations with regard to the influences of the type and thickness of electrolyte on Solid Oxide Fuel Cell Hybrid System (SOFC-HS) performance. A change of electrolyte materials can result in total hybrid system efficiency increasing from around 48&percent; HHV (53&percent; LHV) to about 65&percent; HHV (72&percent; LHV) in an environment where turbine inlet temperature and gas turbine subsystem pressure ratio remain unchanged. The governing equations of SOFC-HS modeling are given. An adequate simulator of the SOFC stack was made and described. Based on this simulator, a model of the 260 kWe Siemens Westinghouse unit was built. The performance of this SOFC-HS with different electrolyte materials and thicknesses is shown, and some characteristics are given and described. The advantages and disadvantages of different electrolyte types from a hybrid system performance point of view are indicated.

This paper proposes a reduced fuel cell stack model for control and fault diagnosis which was validated with experimental data. Firstly, the electro-chemical phenomena are modeled based on a mechanism of gas adsorption/desorption on catalysts at the anode and at the cathode of the stack, including activation, diffusion, and carbon monoxide poisoning. The electrical voltage of a stack cell is then modeled by the difference between the two electrode potentials. A simplified thermal model of the fuel cell stack is also developed in order to take into account heat generation from reactions, heat transfers, and evaporation/condensation of water. Finally, the efficiency ratio is computed as a model output. It is used to evaluate the efficiency changes of the entire system, providing an important indicator for fault detection.

One of the main targets in the development of anode-supported solid oxide fuel cell (SOFCs) is to improve the electrochemical performance. This can be achieved by optimizing processing and microstructural parameters of the SOFCs. Variations of the thickness of the cathode functional layer and the cathode current collector layer, the grain size of the powders used for applying these layers, and the sintering temperature, can influence the electrochemical performance as such that lower operation temperatures become possible without detrimentally affecting the power output to a great extent. In this study the effect of variations of the sintering temperature of the cathode on (1) the microstructure, (2) the gas diffusivity and permeability in the cathode, and (3) electrochemical performance of FZJ-type anode-supported single cells, was investigated. The FZ-Jülich cell design is based on anode-supported type cells, which are characterized by a relatively thick anode (thickness: 1.0-1.5mm) consisting of a NiO/8YSZ cermet, a thin 8YSZ electrolyte, and a bi-layered cathode. The cathode distinguished two separated layers: first a cathode functional layer consisting of La0.65Sr0.3MnO3(LSM)∕Y2O3-stabilized ZrO2 (8YSZ) and a cathode current collector layer of pure La0.65Sr0.3MnO3 (LSM). This study can be considered as a follow-up of that (Journal of Power Sources 141 (2005) 216–226) describing the improvement of the cell performance by a systematic variation of the microstructure. The experiments described in this paper and the corresponding results are part of a more extensive study to investigate in more detail the effect of the sintering temperature on the electrochemical performance of LSM-type SOFCs. Since research is still going on, conclusions, drawn in this contribution, are yet not definitive.

In a situation where fossil energy resources globally run short and the greenhouse effect increases, the interest in new technologies of energy conversion to reduce the demand of primary energy and emission of pollutants grows. The use of high temperature fuel cells like solid oxide fuel cells (SOFCs), especially in combination with gas turbines (GTs), promises remarkable room for improvement in the areas mentioned, compared to other state-of-the-art technologies. But design and handling of such complex plants require efficient control strategies to promote safe and reliable operation. The development of powerful control algorithms is based on an exact knowledge of the operating behavior, which can be obtained using dynamic system models. In this paper a nonlinear model with bulk parameters and 19 dynamic states is presented; the main assumptions and the underlying equations are given. The simulated system consists of a compressor, a SOFC, a turbine, a recuperator, an ejector with a diffusor, a reformer, and a load. Additionally, from the nonlinear model a linear one in state-space representation is derived at nominal conditions. The results of both models are compared. The agreement of the dynamic behavior and of steady state final values is satisfactory. Thus in future studies, methods of linear control theory could be used with the linear model to develop efficient control strategies.

Targets in the development of anode-supported or planar solid oxide fuel cells (SOFCs) are low operation temperatures, high durability, high reliability, high power density, and low production costs. During the past ten years steps have already been taken at Forschungszentrum Jülich to lower the operating temperatures while maintaining the power output. This was achieved by optimizing processing and microstructural parameters of the electrodes. This paper presents the latest results concerning performance improvement through variations of the processing route and the microstructure of La0.65Sr0.3MnO3 (LSM) and La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF)-type SOFCs. In the case of the LSM-type single cells, the following aspects relating to the electrochemical performance were investigated in more detail: (1) production of the anode substrate by tape casting versus warm pressing; (2) deposition of the anode functional layer (AFL) and electrolyte by screen printing versus vacuum slip casting; (3) use of noncalcined and non-ground YSZ for applying the cathode functional layer (CFL); and (4) sintering temperature of the CFL and cathode current collector layer (CCCL). In the case of LSCF-type cells, a systematic approach was initiated for optimizing the Ce0.8Gd0.2O2−δ (CGO) diffusion barrier layer: (1) deposition techniques of the CGO layer and (2) sintering temperature of the screen-printed CGO layer. Results have shown that certain modifications of the processing route led to a slightly lower electrochemical performance, whereas others did not affect the performance at all. Regarding LSCF-type SOFCs, a slight improvement of the performance was achieved by optimizing the sintering temperature of the CGO layer.

Anode recirculation is essential to the pure-hydrogen proton exchange membrane fuel cell system. Keeping the pressure difference between the anode and the cathode is also important to the membrane health. In this paper, a dynamic platform was designed for the recirculation test of injection pump and real-time control of the anode pressure tracking. The test bench can work in a wide range of conditions for high- and low-pressure application. Based on the MATLAB/xPC Target environment, some S functions were written to drive the PC board for the hardware-in-loop application. Then an analytical full-order and a reduced-order model were built with good accuracy. By linearization of the nonlinear dynamic model, a linear quadratic Gaussian algorithm based on state feedback was used for set-point tracking. Moreover, an adaptive fuzzy neural network with an on-line neural network identifier was also designed to improve the control robustness. The foundation of the test bench and realization of the real-time control algorithms are meaningful to the future application in fuel cell systems.

In the paper, a solid oxide fuel cell (SOFC) system is briefly described and its economical feasibility in three different applications is analyzed. In the feasibility analysis, the SOFC system is part of commercial applications where energy is used for power and heat generation. In the economical analysis, the three applications have different load profiles which are studied separately at different geographical locations with associated local energy market conditions. The price for natural gas and electricity varies by location, leading to a different feasibility condition for stationary fuel cell application as well as for other distributed generation equipment. In the study, the spark spread of natural gas and electricity is used as a base variable for the analysis. The feasibility is analyzed in the case of an electricity-only application as well as with two combined heat and power applications, where an economical value is assigned to the produced and consumed heat. The impact on economical competitiveness of possible incentives for the generated fuel cell power is estimated. A sensitivity analysis with different fuel cell-units’ electrical efficiency, maintenance cost, and payback period is presented. Finally, the maximum allowed investment cost levels for the SOFC system at different locations and market conditions is presented.

Project ABSOLUTE (advanced battery solid oxide fuel cell linked unit to maximize efficiency), aims to combine a sodium-nickel chloride battery and an intermediate temperature solid oxide fuel cell (IT-SOFC) to form an all-electric hybrid package that surpasses the efficiency and performance of a purely fuel cell driven vehicle, as well as extending the range of a purely battery driven electric vehicle. This paper discusses the project background, the ABSOLUTE hybrid concept, the methodology adopted, the vehicle types and drive cycles that best suit the hybrid and system control considerations. Results from a battery and IT-SOFC system model are presented.

Pressurized high temperature fuel cells and gas turbine integrated power systems are receiving growing attention as capable of reaching very high electrical conversion efficiency even in small size power plants. In this system the fuel and the oxidant (air) enter the cell after being compressed. The fuel oxidation reaction occurs predominantly within the fuel cell. The reaction is completed in a combustion chamber and the pressurized combustion products are exhausted through a turbine. The dynamic interdependences related to the integration of the fuel cell and the gas turbine are not completely understood and unexpected complications and dangers might arise. In fact as a consequence of both the relatively large volume of the pressurized portion of the plant and the shape of the stalled characteristic of available compressors, the plant could be affected by the inception of fluid-dynamic instabilities. In particular, surge could be detected in the transient off-design operational conditions occurring during plant regulation, start up and shut down. The paper presents a new experimental fuel cell gas turbine simulation facility that has been constructed at the Mechanical Engineering Department of the University of Trieste, Italy. The facility was designed to examine the effects of transient events on the dynamics of these systems. The theoretical analysis of the plant is completed using a dynamic model of the system purposely developed.

An experimental study is under way to assess the performance of solid-oxide cells operating in the steam electrolysis mode for hydrogen production over a temperature range of 800–900°C. Results presented in this paper were obtained from a ten-cell planar electrolysis stack, with an active area of 64 cm2 per cell. The electrolysis cells are electrolyte supported, with scandia-stabilized zirconia electrolytes (∼140 μm thick), nickel-cermet steam/hydrogen electrodes, and manganite air-side electrodes. The metallic interconnect plates are fabricated from ferritic stainless steel. The experiments were performed over a range of steam inlet mole fractions (0.1–0.6), gas flow rates (1000–4000 sccm), and current densities (0–0.38 A/cm2). Steam consumption rates associated with electrolysis were measured directly using inlet and outlet dewpoint instrumentation. Cell operating potentials and cell current were varied using a programmable power supply. Hydrogen production rates up to 100 Nl/h were demonstrated. Values of area-specific resistance and stack internal temperatures are presented as a function of current density. Stack performance is shown to be dependent on inlet steam flow rate.

In the present paper we report the NiO solubility in a variety of alkali carbonate compositions in the presence of MgO, CaCO3, BaCO3, and La2O3 additions under different conditions of gas composition and temperature. Two types of binary eutectic melts were chosen, namely, the standard electrolyte (62-38) (Li-K)2CO3 and (52–48)&percent; (Li-Na)2CO3 mixtures. The ternary eutectic melt chosen was (43.5-31.5-25.0) mol &percent;(Li-Na-K)2CO3. The observed reduction of NiO solubility induced by the additives can be explained in terms of a higher basic character of all the modified electrolytes, although the NiO dissolution still follows an acidic dissolution mechanism in all the conditions under study.