In this paper, a three dimensional solid oxide fuel cell (SOFC) model is constructed to investigate the gas distribution and the pressure variation in the external manifold stack by a computational fluid dynamics (CFD) approach. Several geometric parameters of external manifold stack, including the position of inlet tube, depth of the manifold and the channel resistance are optimized to achieve uniform gas distributions among the channels. Simulation results indicate that a gas distributor can enhance the flow uniformity effectively. Besides, with the increasing depth of the manifold, the flow tends to be more uniform in T-manifold but has a small impact on C-manifold stack. It is also shown that flow distribution is intensively enhanced with the raise of resistance, especially from 0Pa to 100Pa. Modeling results highlight the importance of manifold and channel structure design for external manifold stack and can be widely applied to design the geometric parameters.

With the advantages of high power density, rapid startup, low operating temperature and no emission of pollutants, proton exchange membrane (PEM) fuel cell is considered to be the most promising candidate for the next generation power source of Clean Energy Automotive. PEM fuel cell operation necessitates thermal management to satisfy the requirements of safe and efficient operation by keeping the temperature within a certain range independent of varying load conditions. As for a high power PEM fuel cell system (eg. 80kw) without the external gas to gas humidifier, the temperature of the stack inlet coolant had better track to a time-varying curve produced by the working condition, which introduce the temperature difference between the cathode inlet and outlet, and thus it improves the relative humidity of the inlet air of the cathode. Compared to the traditional stack outlet coolant temperature regulation problem, the new plant is a two inputs and two outputs system, furthermore, the stack inlet coolant temperature control is a tracking problem which is different to the outlet coolant temperature regulation (regulation problem). Considering that the PEM fuel cell without the external humidifier is a promising scheme which has been adopted by the Mirai fuel cell vehicle [1], we actively aim to control both the inlet and outlet coolant temperature as desired simultaneously. In this paper, a two inputs and two outputs decouple control scheme is developed to achieve our aim. Firstly, based on the energy conservation and continuity equation, we establish a dynamic thermal model for the cooling system consisted of a water circulation pump and a radiator coupled to a fan, integrated with the fuel cell stack. Secondly, the static coupling characteristics of the control variable is analyzed according the relative gain matrix method. Then two specific control strategies are designed. One is based on frequency domain pure PID control technique. Considering the coupling phenomenon between two control channels, another technique is based on decouple theory feed-forward decouple control technique. Both of them try to regulate the outlet and inlet coolant temperature through tuning mass flow rate of water circulation pump and duty ratio of radiator. Finally, all the control strategies are demonstrated on the platform of Matlab / Simulink. The results show that both of them can control the stack inlet and outlet coolant temperature simultaneously, but the second strategy has much better performance than the first.

The authors develop a small and simple steam-reforming reactor in a home-use size for such various heavy-hydrocarbons fuels as n-octane, n-decane, n-tetradecane and n-hexadecane in addition to n-dodecane, and measure the inside-temperature profile and the molar fractions of main gas components such as H 2 , CH 4 , CO and CO 2 . As a result, the authors successfully achieve suitable inside-temperature profiles. Namely, temperature almost-linearly increases in the downstream direction along a reactor, under such two conditions as 600–950 K at the upstream end of the catalyst-layer bed in the reactor and as less-than 1,070 K everywhere in the reactor. And, the authors reveal the effects of the liquid-hourly space velocity (LHSV) upon the molar fractions, a conversion ratio and reforming efficiencies for various heavy-hydrocarbons fuels. All the molar fractions, which agree well with thermochemical-equilibrium theory, are approximately independent of LHSV . The conversion ratio is about 90 % for LHSV ≤ 0.6 h −1 , and monotonically decreases with increasing LHSV for LHSV > 0.6 h −1 . Then, each reforming efficiency always attains the maximum for LHSV ≈ 0.6 h −1 being independent of fuels. This suggests the common upper limit of LHSV for practically-suitable operation.

Transients in a hybrid system composed of a solid oxide fuel cell (SOFC) and a gas turbine (GT) were evaluated during simultaneous manipulation of system airflow bypasses and turbine electric load. The three airflow bypass valves selected for study were chosen for their potential application in controlling dynamic excursions of the main fuel cell and gas turbine parameters in the system. The objective of this work was to understand the physical behavior by the simultaneous operation of the bypass valves along with the turbine electric load in order to formulate scenarios of control on the key parameters relevant to system failure, specifically from compressor stall and surge. Empirical data was collected using the National Energy Technology Laboratory Hybrid Performance project hardware simulation of a SOFC/GT hybrid. Step changes were implemented in all three valves for various open/close valve commands and increase/decrease of the turbine electric load simultaneously. The transient response of process variables was analyzed to determine the potential for mitigating or aggravating compressor stall and surge during load excursions.

Jet fuel is used to produce hydrogen on board of vehicles through integrated reactions of autothermal reforming (ATR) and water-gas shift (WGS). One of the most attractive benefits of autothermal reforming of hydrocarbon fuels is the possibility of self-sustainability of the reaction if the process is carefully managed and designed. In this work, an integrated fuel processor, including a mixing zone, an ATR reactor, a WGS reactor and two recuperators was fabricated and the hydrogen production performance (using Jet fuel) was tested and studied. Analysis of the energy in reactions and heat transfer area in the heat recuperator was carried out in order to obtain some insights on the optimal design and operating conditions. The previous experimental results regarding the reformate compositions and fuel conversion efficiency were used to evaluate some of the parameters described in the energy analysis model. The predicted results show that the overall process heat was negative (exchanging heat larger than preheating heat) under most of the previous experimental conditions, indicating the potential of self-sustainability of reaction in the fuel processor.

Considerable waste heat is generated via the oxygen reduction reaction in polymer electrolyte membrane fuel cells. Consequently, heat generation and removal in conventional fuel cell architectures has been carefully investigated in order to achieve effective thermal management. Here we present a novel microscale fuel cell design that utilizes a half-membrane electrode assembly. In this design, a single fuel/electrolyte stream provides an additional pathway for heat removal that is not present in traditional fuel cell architectures. The model presented here investigates heat removal over a range of inlet fuel temperatures. Heat generation densities are determined experimentally for all inlet fuel temperatures. The simulations presented here predict thermal profiles throughout this microscale fuel cell design. Simulation results show that the fuel stream dominates heat removal at room temperature. As inlet fuel temperature increases, the majority of heat removal occurs via convection with the ambient air. The model also shows that heat transfer through the oxidant channel is minimal over the range of inlet fuel temperatures.

A three dimensional numerical model of a practical planar solid oxide fuel cell (SOFC) stack based on the finite element method is constructed to analyze the thermal stress generated at different uniform temperatures. Effects of cell positions, different compressive loads, and coefficient of thermal expansion (CTE) mismatch of different SOFC components on the thermal stress distribution are investigated in this work. Numerical results indicate that the maximum thermal stress appears at the corner of the interface between ceramic sealants and cells. Meanwhile the maximum thermal stress at high temperature is significantly larger than that at room temperature (RT) and presents linear growth with the increase of operating temperature. Since the SOFC stack is under the combined action of mechanical and thermal loads, the distribution of thermal stress in the components such as interconnects and ceramic sealants are greatly controlled by the CTE mismatch and scarcely influenced by the compressive loads.

Polymer electrolyte membrane (PEM) fuel cells have been explored as a clean battery replacement in portable and miniature applications where total system mass and specific energy density (Wh/kg) are critical design constraints. By coupling a boost (step-up) DC/DC converter with a miniature PEM fuel cell stack, the total power system mass can be reduced while providing voltage regulation capabilities not available with a fuel cell alone. This configuration is applied to the design of a controlled meteorological (CMET) balloon power system as a case-study. In this work, we designed and tested three different micro-power DC/DC boost converters that were deployed in series with a PEM fuel cell stack. Testing of the converters revealed a transition region in which the converter output voltage is hysteretic, not well regulated, and dependent on the input voltage. As a result, it is important to identify the minimal stable and reliable input voltage to a given DC/DC converter in order to minimize the fuel cell power system mass. An optimization strategy is presented here that enables the minimization of PEM fuel cell stack mass by identifying the appropriate DC/DC converter input voltage subject to the dimension constraints of the fuel cell components. Prototype DC/DC converters were then experimentally tested in direct connection to a miniature two-cell PEM fuel cell stack.

To improve the energy efficiency and achieve zero-net energy goals, as well as to reduce environmental impacts, we demonstrated and evaluated the use of a 1.5 kW Solid Oxide Fuel Cell (SOFC) with Micro-combined heat and power (Micro-CHP) for powering residential homes. In this study, we designed, tested and demonstrated an SOFC Micro-CHP system as a Distributed Generation (DG) prime mover that has high reliability and availability, high efficiency and ultra-low emissions for steady state operation. Energy balances and dynamic analyses of integrating a thermal storage system with the SOFC Micro-CHP system were carried out using a summer load profile of a residence in Southern California. The thermal storage system was found to mitigate the dynamics introduced from the electric water heater and smooth out the residential load profile. Additionally, the integrated thermal storage system and the SOFC Micro-CHP system was found to reduce the overall electricity import and thus the carbon emissions.

Operating points of a 300kW Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) power plant simulator is estimated with the use of a Multiple Model Adaptive Estimation (MMAE) algorithm, aimed at improving the flexibility of controlling the system to changing operating conditions. Through a set of empirical Transfer Functions derived at two distinct operating points of a wide operating envelope, the method demonstrates the efficacy of estimating online the probability that the system behaves according to a predetermined dynamic model. By identifying which model the plant is operating under, appropriate control strategies can be switched and implemented upon changes in critical parameters of the SOFC-GT system — most notably the Load Bank (LB) disturbance and FC cathode airflow parameters. The SOFC-GT simulator allows testing of various fuel cell models under a cyber-physical configuration that incorporates a 120kW Auxiliary Power Unit, and Balance-of-Plant components in hardware, and a fuel cell model in software. The adaptation technique is beneficial to plants having a wide range of operation, as is the case for SOFC-GT systems. The practical implementation of the adaptive methodology is presented through simulation in the MATLAB/SIMULINK environment.

A tri-layered solid electrolyte and an oxygen permeable solid air cathode for lithium-air battery cells were synthesized in this investigation. Detailed fabrication procedures for solid electrolyte, air cathode and the assembly of real-world lithium-air battery cell are described. Fabrication of real-world lithium-air button cells was performed using the synthesized tri-layered solid electrolyte, an oxygen permeable air cathode, and a metallic lithium anode. The lithium-air button cells were tested under dry air with 0.1mA∼0.2mA discharge/charge current at different temperatures. It was found that interfacial contact resistances play an important role in Li-air battery cell performance. Experimental results suggested that the lack of robust interfacial contact among solid electrolyte, air cathode and lithium metal anode were the primary factors for the cell’s high internal resistances. It was also found that once the cell internal resistance issues were resolved, the discharge curve of the battery cell was much smoother and the cell was able to discharge at above 2.0V for up to 40 hours. It indicated that in order to have better performing lithium-air battery cell, interfacial contact resistances issue must be resolved very efficiently.

DEMOSOFC [1] is a Fuel Cell & Hydrogen Joint Undertaking (FCH-JU) funded project which foresees the installation of the largest biogas fed Solid Oxide Fuel Cell (SOFC) in Europe. The SOFC will be the sole combined heat & power (CHP) generator within a medium size wastewater treatment plant (WWTP) located in Torino (IT). Three SOFC modules, each rated 58 kWe, will supply around 30% of the internal electrical loads and a variable share of the thermal load depending on the season. The key objective of the project is to demonstrate the industrial readiness of SOFC systems, which are able to guarantee better performance both in terms of electrical efficiency and emission of pollutants with respect to conventional internal combustion engines. SOFC systems have a high potential for integration with local renewable fuels as biogas and/or bio-syngas from waste sources. Looking at the biogas potential in EU, the most common plant size lies in the sub-MW scale. This work aims to describe the DEMOSOFC concept, the approach followed for the design of the integrated system. Energy performance, environmental benefits, underlining advantages and barriers of this integration are presented and discussed.

This paper proposes an optimal predictive control of 0.75 kW PEM fuel-cell cogeneration with home appliances. This paper also models fuel cell system for design and operation evaluation of building equipment based on actual measurement of residential fuel cell system on sale. As one application of constructed model and proposed control method, this paper discusses concerning home EMS for efficient PV utilization.

The performance of a 300 kW Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) pilot power plant simulator is evaluated by applying a set of robust Proportional Integral Derivative (PID) controllers that satisfy time delay and gain uncertainties of the SOFC-GT system. The actuators are a fuel valve (FV) that models the fuel cell thermal exhaust, and a cold-air (CA) valve which bypasses airflow rate from the fuel cell cathode. The robust PID controller results for the uncertain gains are presented first, followed by a design for uncertain time delays for both, FV and CA bypass valves. The final design incorporates the combined uncertain gain parameters with the time delay modeling of both actuators. This Multiple-Input Multiple-Output (MIMO) technique is beneficial to plants having a wide range of operation and a strong parameter interaction. The practical implementation is presented through simulation in the Matlab/Simulink environment.

Recent developments in applications such as Pulsed Power, Space, High Altitude Long Endurance (HALE) aircraft and underwater vehicles have created interest in the application of air-independent fuel cells. The attraction for such systems has been the potential for high performance, long life and high energy density allowing for extended mission operations and simple recharge. A limitation of such systems, to date, has been the relatively complicated balance of plant required for system operation. This typically requires circulation of one or both reactants to remove product water and distribute reactants. These parasitic systems can reduce the overall efficiency and maintainability of the system, create noise and inhibit or prevent certain missions. Under the sponsorship of the NASA Glenn Research Center Infinity has developed a Non Flow-Through (NFT) Advanced Product Water Removal (APWR) Proton Exchange Membrane Fuel Cell system. The design eliminates the need to actively circulate reactants and can remove water directly from the reaction site within the cell. This low temperature, compact, lightweight technology projects to a system with the operational simplicity and reliability of a battery but with the performance and recharge capability of fuel cells. This paper will report on the operational characteristics, performance and benefits of Infinity’s APWR fuel cell. An update on development status and recent testing results will be included.

The high thermal conduction resistances of lithium-ion batteries severely limits the effectiveness of conventional external thermal management systems. To remove heat from the insulated interior portions of the cell, a large temperature difference is required across the cell, and the center of the electrode stack can exceed the thermal runaway onset temperature even under normal cycling conditions. One potential solution is to remove heat locally inside the cell by evaporating a volatile component of the electrolyte. In this system, a high vapor pressure co-solvent evaporates at a low temperature prior to triggering thermal runaway. The vapor generated is transported to the skin of the cell, where it is condensed and transported back to the internal portion of the cell via surface tension forces. For this system to function, a co-solvent that has a boiling point below the thermal runaway onset temperature must also allow the cell to function under normal operating conditions. Low boiling point hydrofluoroethers (HFE) were first used by Arai to reduce LIB electrolyte flash points, and have been proven to be compatible with LIB chemistry. In the present study, HFE-7000 and ethyl methyl carbonate (EMC) 1:1 by volume are used to solvate 1.0 M LiTFSI to produce a candidate electrolyte for the proposed cooling system. Copper antimonide (Cu 2 Sb) and lithium iron phosphate (LiFePO 4 ) are used in a full cell architecture with the candidate electrolyte in a custom electrolyte boiling facility. The facility enables direct viewing of the vapor generation within the full cell and characterizes the galvanostatic electrochemical performance. Test results show that the LFP/Cu 2 Sb cell is capable of operation even when a portion of the more volatile HFE-7000 is continuously evaporated.

Demand has increased for high reliability mobile power systems for space and aerial vehicles in military, scientific, and commercial applications. Batteries have traditionally supplied power in these applications, but the desire to extend mission duration and expand vehicle capabilities would require an energy density increase that is difficult for batteries to achieve. The use of pure hydrogen and oxygen reactants with high efficiency membrane electrode assemblies and novel design concepts for the fuel cell stack bipolar plates and balance of plant (BOP) components has the potential to meet the desired system energy density. This paper reviews subsystem and integrated testing of a lightweight PEM fuel cell system design for implementation into an aerial vehicle or space mission. The PEM fuel cell stack is designed for optimum efficiency at 2 kWe of power during standard operation with the capacity to provide over 5 kWe of continuous power. The passive flow control and water management subsystems provide the gas flow and humidification necessary for efficient operation and remove excess water produced by the stack under all operating regimes. Work is in progress to test the fully integrated system under expected operating conditions for potential lightweight PEMFC applications.

Hydrogen fuel cells are an important part of a portfolio of strategies for reducing petroleum use and emissions from medium and heavy duty (MD and HD) vehicles; however, their deployment is very limited compared to other powertrains. This paper addresses gaseous hydrogen storage tank design and location on representative MD and HD vehicles. Storage design is based on vehicle size and occupation. The available storage space on representative vehicles is assessed and is used to estimate the weight and capacity of composite material-based compressed gaseous storage at 350 and 700 bar. Results demonstrate the technical feasibility of using hydrogen storage for Fuel Cell Electric Trucks (FCETs) across a wide range of the MD and HD vehicle market. This analysis is part of a longer-term project to understand which market segments provide the maximum economic impact and greenhouse gas reduction opportunities for FCETs.

In this study, the catalytic combustion of methane is numerically investigated using an unstructured, implicit, fully coupled finite volume approach. Nonlinear system of equations is solved by Newton’s method. The catalytic partial oxidation of methane over both platinum and rhodium catalysts are studied three-dimensionally. Eight gas-phase species (CH 4 , CO 2 , H 2 O, N 2 , O 2 , CO, OH and H 2 ) are considered for the simulation. Surface chemistry is modeled by detailed reaction mechanisms including 24 heterogeneous reactions with 11 surface-adsorbed species for Pt catalyst and 38 heterogeneous reactions with 20 surface-adsorbed species for Rh catalyst. The numerical results are compared with the experimental data and good agreement is observed. The performance of the fuel reformer is analyzed for two different catalysts. The sensitivity analysis for the reactor is performed using three different approaches: finite difference, direct differentiation and adjoint method. The design cycle is performed using two gradient-based optimization algorithms to improve the value of the implemented cost function and optimize the reactor performance.

In this paper, using patented nano-additive based polymer synthesis technology, a novel approach to the design and fabrication of high temperature proton exchange membrane (PEM) has been developed. The presence of sulfonated octaphenyl POSS (S-POSS) in a PBI-PA (polybenzimidazole-phosphoric acid) membrane results in a 40–50% increase in conductivity at 120–200$deg relative to non-sulfonated silica or POSS control fillers at comparable weight percent filler loadings and PBI molecular masses, and also relative to unfilled PBI-PA membranes. In addition, the presence of S-POSS and silica both result in physical reinforcement of the membrane and increased its modulus and mechanical integrity, but only S-POSS offers the benefits of both increased conductivity and increased modulus. Isophthalic acid and 3,3’-diaminobenzidine (DAB) were polymerized in the presence of polyphosphoric acid (PPA) and S-POSS nanoadditive, and the degree of polymerization was monitored by viscosity and torque change measurements. Molecular mass was determined by inherent viscosity measurements of samples removed from the reaction solution. Membranes were prepared by casting the reaction solution and allowing PPA to hydrolyze to PA under ambient conditions. The membranes were characterized for acid content, in-plane conductivity, tensile modulus and shear modulus, and were roll-milled to achieve the desired thickness for membrane electrode assembly (MEA) fabrication.