Fuel Cell Auxiliary Power Unit Research Articles

A Compact, Self-Sustaining Fuel Cell Auxiliary Power Unit Operated on Diesel Fuel

A complete fuel cell-based auxiliary power unit in the 7.5 kWe power class utilizing diesel fuel was developed in accordance with the power density and start-up targets defined by the U.S. Department of Energy. The system includes a highly-integrated fuel processor with multifunctional reactors to facilitate autothermal reforming, the water-gas shift reaction, and catalytic combustion. It was designed with the help of process analyses, on the basis of which two commercial, high-temperature PEFC stacks and balance of plant components were selected. The complete system was packaged, which resulted in a volume of 187.5 l. After achieving a stable and reproducible stack performance based on a modified break-in procedure, a maximum power of 3.3 kWe was demonstrated in a single stack. Despite the strong deviation from design points resulting from a malfunctioning stack, all system functions could be validated. By scaling-up the performance of the functioning stack to the level of two stacks, a power density of 35 We l−1 could be estimated, which is close to the 40 We l−1 target. Furthermore, the start-up time could be reduced to less than 22 min, which exceeds the 30 min target. These results may bring diesel-based fuel cell auxiliary power units a step closer to use in real applications, which is supported by the demonstrated indicators.

Kinetic modeling of diesel autothermal reforming for fuel cell auxiliary power units

Fuel cell auxiliary power unit (FC-APU) system for heavy-duty trucks has been attracting much attention as an alternative to engine idling to reduce pollutant emissions. In this system, a reformer, which converts diesel, the main fuel of heavy-duty trucks, into syngas suitable for the fuel cell, is essential. A kinetic model of the reforming can be helpful in tasks such as the reactor design and system operation, but it is highly challenging to develop such a model due to the complexity of the reforming reaction network. Thus, in this study, we propose a systematic approach to build a reduced kinetic model of the diesel autothermal reformer. Specifically, microreactor experiments are conducted using a commercial diesel fuel, where the temperature, oxygen-to-carbon ratio (OCR), and steam-to-carbon ratio (SCR) are varied. Then, based on the composition measurements of the exit gas, optimal kinetic models are constructed by iteratively solving a parameter estimation problem for the candidate kinetic models with varying number of reactions. To reduce the number of candidates significantly, lumping techniques are used to generate reduced kinetic models. A stochastic optimization method is employed for the parameter estimation in which the concept of cross-entropy is used. The optimal reduced kinetic models with 3 and 4 reactions showed a consistency with the literature in terms of the reactions included. The accuracy of optimal reduced kinetic models increased, showing 21% improvement as the number of reactions increased from 3 to 4.

A Model-based Scenario Analysis for Assessing the Benefits of Fuel Cell Vehicle Hybridization

Abstract The paper presents model-based scenario analyses of micro and mild tri-hybrid vehicle configurations, related to existing conventional vehicles equipped with small power proton exchange membrane (PEM) fuel cell (FC) systems and, eventually, additional battery pack. The analyses are intended to support short-to medium-term development of fuel cell powered Light Duty Vehicles (LDVs) technology and are useful for carmakers to quantitatively assess the potential advantages associated to the afore-mentioned opportunities in terms of short-term clean and cost-efficient production of hydrogen. The analyses are performed making use of a comprehensive vehicle model, based on a hybrid (black-box and lumped parameters) approach, of a medium passenger car equipped with a turbocharged SI engine. The model has been enhanced to account for the additional components of two different powertrain configurations, namely conventional powertrain with ICE and fuel cell Auxiliary Power Unit (APU) and hybrid powertrain ICE/FC. Simulations have been carried out vs. standard driving cycles for two energy management strategies. The results allow evaluating the impact of powertrain configuration on CO2 emissions, in case of both Tank-to-Wheel (TTW) and Well-to-Wheel (WTW) analyses.

Heat exchanger design for autothermal reforming of diesel

The increasing electrification of vehicles for passenger and heavy duty transport requires the deployment of efficient, low-emission power sources. Auxiliary Power Units (APUs) based on fuels cells offer an excellent solution, especially for supplying power during idling mode. For urban transport applications, gaseous hydrogen appears to be the best fuel option, whereas long-distance applications are better served by a liquid energy carrier. The autothermal reforming of liquid fuels such as diesel presents a simple and efficient method for producing hydrogen for fuel cell APUs. Heat integration for steam generation and air pre-warming are the key elements to a compact autothermal reformer design. With the aid of intense CFD simulations, a reformer construction was achieved with the high power density of 3.3 kWth/l. Experimental validation indicates high hydrogen concentrations of between 32 and 36%, depending on diesel quality. In combination with already existing results, the newest autothermal reformer (ATR) generation enables the set-up of a complete APU system, fulfilling the U.S. Department of Energy (DOE) targets for fuel cell-based APUs.

A Diesel-Powered Fuel Cell APU—Reliability Issues and Mitigation Approaches

The paper deals with reliability issues of a diesel-powered fuel cell auxiliary power unit (APU). The unit combines an autothermal diesel reformer and a proton exchange membrane fuel cell stack. The focal point is mitigation approaches for increasing the reliability of the complete APU system. These include control strategies on the one side, and electronic hardware solutions on the other. The measures, guarantying safe, reliable, and long-life operation, were developed, implemented and experimentally validated on a 3-kW net electric power APU system targeted for truck on-board applications.

Control of an afterburner in a diesel fuel cell power unit under variable load

Abstract In this paper, the control system for a catalytic afterburner in a diesel fuel cell auxiliary power unit is presented. The catalytic afterburner is used to burn the non-utilised hydrogen and other possible combustible components of the fuel cell anode off-gas. To increase the energy efficiency of the auxiliary power unit, the thermal energy released in the catalytic afterburner is utilised to generate the steam for the fuel processor. For optimal operation of the power unit in all modes of operation including load change, stable steam generation is required and overall energy balance must be kept within design range. To achieve this, the reaction temperature of the catalytic afterburner must be stable in all modes of operation. Therefore, we propose the afterburner temperature control based on mass and thermal balances. Finally, we demonstrate the control system using the existing prototype of the diesel fuel cell auxiliary power unit.

Coupling of a Solid Oxide Fuel Cell Auxiliary Power Unit with a Vapour Absorption Refrigeration System for Refrigerated Truck Application

AbstractModeling studies have been carried out to investigate coupling of an solid oxide fuel cell auxiliary power unit (SOFC APU) with a small scale NH3–H2O based vapour absorption refrigeration system (VARS) for a refrigerated truck/trailer application, by using hot cathode exhaust from the SOFC stack to drive the VARS. A bottom up design and modeling approach has been adopted where the end requirements, cooling load in this case, are identified first followed by upstream modeling of the SOFC and VARS unit. This approach enables design of system/components to meet the desired end requirements rather than compromise or fall short of the desired goal.Initial modeling results show that it is indeed possible to couple an SOFC with a VARS on a small scale (< 10 kW cooling load) for the refrigerated truck application. As this novel strategy utilizes both heat and power from the SOFC it promises a higher total efficiency up to 80% and also removes a significant part of the load from the main diesel engine, thereby leaving the engine to carry out the task of only propelling the vehicle. The excess electrical power from the SOFC could also be used to charge the vehicle batteries.

Control of autothermal reforming reactor of diesel fuel

In this paper a control system for autothermal reforming reactor for diesel fuel is presented. Autothermal reforming reactors and the pertaining purification reactors are used to convert diesel fuel into hydrogen-rich reformate gas, which is then converted into electricity by the fuel cell. The purpose of the presented control system is to control the hydrogen production rate and the temperature of the autothermal reforming reactor. The system is designed in such a way that the two control loops do not interact, which is required for stable operation of the fuel cell. The presented control system is a part of the complete control system of the diesel fuel cell auxiliary power unit (APU).

Parametric analysis of a solid oxide fuel cell auxiliary power unit operating on syngas produced by autothermal reforming of hydrocarbon fuels

A 1 kWe integrated auxiliary power unit (APU) system consisting of an autothermal reformer and a solid oxide fuel cell (SOFC) unit, as well as balance-of-plant components, was designed and analyzed. A relatively easy-to-approach SOFC model was developed in order to conveniently calculate V-I and P-I curves and the system's net efficiency at different operating conditions. The effects of steam to carbon and oxygen to carbon ratios in the reactants, channel dimensions of the SOFC unit, and hydrocarbon fuel types on the integrated APU system's performance were discussed. Five hydrocarbon fuels including diesel, Jet-A, gasoline, ethanol, and methanol were studied as fuel sources for the APU system. The system's net efficiency around 35% is possible for all the tested fuels in the current density range of 100–400 mA/cm2. The APU system was also verified to be thermally self-sustainable in the steady state operation by a thermal management analysis.

Demonstration of the First European SOFC APU on a Heavy Duty Truck

Within the EU-FCH JU funded project DESTA the partners AVL, Eberspächer, Topsoe Fuel Cell, Volvo and Forschungszentrum Jülich are collaborating since January 2012 to demonstrate the first European Solid Oxide Fuel Cell Auxiliary Power Unit (SOFC APU) on a heavy duty truck. The APU is used to provide the truck with electrical energy during vehicle standstill to power comfort functions like A/C, TV, refrigerator & PCs. To facilitate these functionalities typically, the main diesel engine is idled which causes significant emissions and operating cost. The APU is used with conventional diesel fuel and provides about 3 kW of electrical power at 30% electrical efficiency. To enable the usage of conventional fuel, SOFC technology is used.Main advantage of the SOFC stack technology is the use and operation with synthesis gas generated out of conventional fuels. Hence DESTA SOFC APU systems can be operated with conventional road Diesel fuel. Within the APU system, the Diesel fuel is reformed to a hydrogen and carbon monoxide containing synthesis gas. The SOFC technology allows the conversion of this hydrogen and also carbon monoxide with oxygen of the air directly into electricity. This creates a significant benefit in comparison to other fuel cell technologies like PEM or HT PEM. This process also allows significantly higher electrical efficiencies than conventional solutions like a diesel gen-set. Additionally the fuel cell APU is extremely silent and doesn’t emit other harmful emissions like NOx, THC or PM.

Fuel Cell Auxiliary Power Units for Heavy Duty Truck Anti-Idling

Fuel Cell Auxiliary Power Units for Heavy Duty Truck Anti-Idling

Integrated fuel cell APU based on a compact steam reformer for diesel and a PEMFC

This paper presents experimental results of a diesel steam reforming fuel processor operated in conjunction with a gas cleanup module and coupled operation with a PEM fuel cell. The fuel processor was operated with two different precious-metal based reformer catalysts, using diesel surrogate with a sulfur content of less than 2ppmw as fuel. The first reformer catalyst entails an increasing residual hydrocarbon concentration for increasing reformer fuel feed. The second reformer catalyst exhibits a significantly lower residual hydrocarbon concentration in the reformate gas.Coupled operation of the fuel processor/gas cleanup with a PEM stack shows the impact of residual hydrocarbons on fuel cell performance. Using the second reformer catalyst, the fuel processor/gas cleanup was successfully coupled to an 80-cell stack generating an electric power output of up to 1.5kWel. The system is foreseen to be used as a mobile auxiliary power unit (APU) for caravans and yachts or as a stationary energy supply.

Development and design of experiments optimization of a high temperature proton exchange membrane fuel cell auxiliary power unit with onboard fuel processor

In this work, the concept development, system layout, component simulation and the overall DOE system optimization of a HT-PEM fuel cell APU with a net electric power output of 4.5 kW and an onboard methane fuel processor are presented. A highly integrated system layout has been developed that enables fast startup within 7.5 min, a closed system water balance and high fuel processor efficiencies of up to 85% due to the recuperation of the anode offgas burner heat. The integration of the system battery into the load management enhances the transient electric performance and the maximum electric power output of the APU system. Simulation models of the carbon monoxide influence on HT-PEM cell voltage, the concentration and temperature profiles within the autothermal reformer (ATR) and the CO conversion rates within the watergas shift stages (WGSs) have been developed. They enable the optimization of the CO concentration in the anode gas of the fuel cell in order to achieve maximum system efficiencies and an optimized dimensioning of the ATR and WGS reactors. Furthermore a DOE optimization of the global system parameters cathode stoichiometry, anode stoichiometry, air/fuel ratio and steam/carbon ratio of the fuel processing system has been performed in order to achieve maximum system efficiencies for all system operating points under given boundary conditions.

Study on Use of Fuel-Cell Auxiliary Power Units in Refrigerator Cars Employed for Delivery to Convenience Store

Study on Use of Fuel-Cell Auxiliary Power Units in Refrigerator Cars Employed for Delivery to Convenience Store

A techno-economic comparison of fuel processors utilizing diesel for solid oxide fuel cell auxiliary power units

Ultra-low sulphur diesel (ULSD) is the preferred fuel for mobile auxiliary power units (APU). The commercial available technologies in the kW-range are combustion engine based gensets, achieving system efficiencies about 20%. Solid oxide fuel cells (SOFC) promise improvements with respect to efficiency and emission, particularly for the low power range. Fuel processing methods i.e., catalytic partial oxidation, autothermal reforming and steam reforming have been demonstrated to operate on diesel with various sulphur contents. The choice of fuel processing method strongly affects the SOFC's system efficiency and power density. This paper investigates the impact of fuel processing methods on the economical potential in SOFC APUs, taking variable and capital cost into account. Autonomous concepts without any external water supply are compared with anode recycle configurations. The cost of electricity is very sensitive on the choice of the O/C ratio and the temperature conditions of the fuel processor. A sensitivity analysis is applied to identify the most cost effective concept for different economic boundary conditions. The favourite concepts are discussed with respect to technical challenges and requirements operating in the presence of sulphur.

Nanoparticle Molybdenum Dioxide: A New Alternative Catalytic Material for Hydrogen Production via Partial Oxidation of Jet-A Fuels

A battery-extender fuel cell auxiliary power unit (BE-APU) is the first step in a far-reaching and long-term vision that Boeing has for utilizing fuel cells as APUs on board commercial airplanes for greater energy efficiency and improved air quality at airports. A critical requirement for developing a commercially viable BE-APU is a catalyst that can reform and electrochemically oxidize fossil fuel-based aviation fuels. This paper reviews the catalytic performance of nanoparticle MoO 2 , which can effectively reform Jet-A fuels to produce hydrogen and carbon monoxide (synthesis gas) under partial oxidation conditions. Nanoparticle MoO 2 was synthesized by the reduction of molybdenum trioxide (MoO 3 ) powder in a 1:3 volume ratio of ethylene glycol to distilled water at 180 °C for 12 h. The resulting nanoparticle MoO 2 was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and BET surface area measurements. For the partial oxidation of Jet-A fuel at 850 °C, oxygen-to-carbon (O 2 /C) ratio of 0.55 and weight-hourly-space-velocity (WHSV) of 1.5 h ―1 , the synthesized nanoparticle MoO 2 displayed a fuel conversion of ∼99% and a hydrogen yield of ∼60% after 9 h on-stream. Under similar operating conditions, a reference Ni catalyst was deactivated due to coking after less than 4 h of operation. Based on these findings, nanoparticle MoO 2 appears to display a coking resistance higher than that of the reference Ni catalyst during the partial oxidation of Jet-A fuels.

Effects of stack array orientation on fuel cell efficiency for auxiliary power unit applications

The commercial fuel cell products currently appearing on the market are self-contained fuel cell engines. These engines can be used for many applications that are presently dominated by internal combustion engines or batteries. Vehicle mounted fuel cell auxiliary power units have been attracting attention lately. Additionally, there is a market based incentive to use multiple small fuel cell arrays in place of a single large fuel cell for some applications. Typically, fuel cells are designed to operate as stand-alone units. This paper investigates the ability of small commercial stacks to operate in common array arrangements. Although an individual Nexa is able to produce 1500 W, Dual Nexas do not maintain that capability while in array configurations. With an overall load share ratio of 1.02:1 the series array reliably produced 2900 W of power, while with an overall load share ratio of 1.09:1 the parallel array reliably produced only 2800 W of power. This study shows that array orientation affects both system stack net efficiency and individual stack net efficiency. The information gained from this study may be helpful for fuel cell design and integration.

Diesel reformer — a key component for a truck fuel cell APU

A diesel fuel processor has been developed to integrate with a high-temperature polybenzimidazole (PBI) based polymer electrolyte membrane (PEM) fuel cell, to provide power for truck auxiliary power unit (APU) applications. The fuel processor is designed to operate at low temperatures, ranging from 490 to 600°C, and convert ultra low sulfur diesel (ULSD) to C1 (CH4, CO and CO2) compounds without intermediate products. Reforming in this low temperature range is an effective approach to minimizing carbon deposition. It also produces less CO in the product; consequently the CO cleanup component is greatly simplified when the system is integrated with a PBI fuel cell that tolerates some CO. This reduction in system complexity will help lower costs while improving reliability.

Control Oriented Modeling of Solid Oxide Fuel Cell Auxiliary Power Unit for Transportation Applications

This paper reports on the development of a control-oriented model for simulating a hybrid auxiliary power unit (APU) equipped with a solid oxide fuel cell (SOFC) stack. Such a work is motivated by the strong interest devoted to SOFC technology due to its highly appealing potentialities in terms of fuel savings, fuel flexibility, cogeneration, low-pollution and low-noise operation. In this context, the availability of a model with acceptable computational burden and satisfactory accuracy can significantly enhance both system and control strategy design phases for APUs destined to a wide application area (e.g., mild-hybrid cars, trains, ships, and airplanes). The core part of the model is the SOFC stack, surrounded by a number of ancillary devices: air compressor/blower, regulating pressure valves, heat exchangers, prereformer, and postburner. Since the thermal dynamics is clearly the slowest one, a lumped-capacity model is proposed to describe the response of SOFC and heat exchangers to load (i.e., operating current) variation. The stack model takes into account the dependence of stack voltage on operating temperature, thus adequately describing the typical voltage undershoot following a decrease in load demand. On the other hand, due to their faster dynamics the mass transfer and electrochemistry processes are assumed instantaneous. The hybridizing device, whose main purpose is to assist the SOFC system (i.e., stack and ancillaries) during transient conditions, consists of a lead-acid battery pack. Battery power dependence on current is modeled, taking into account the influence of actual state of charge on open circuit voltage and internal resistance. The developed APU model was tested by simulating typical auxiliary power demand profiles for a heavy-duty truck in parked-idling phases. Suited control strategies also were developed to avoid operating the SOFC stack under severe thermal transients and, at the same time, to guarantee a charge sustaining operation of the battery pack. In order to assess the benefits achievable by introducing the SOFC-APU on board of a commercial truck, the simulated fuel consumption was compared with the fuel consumed by idling the thermal engine. From the simulation carried out, it emerges how the SOFC-APU allows achieving a potential reduction in fuel consumption of up to 70%.

Analysis of the market for diesel PEM fuel cell auxiliary power units onboard long-haul trucks and of its implications for the large-scale adoption of PEM FCs

Proton exchange membrane fuel cells (PEM FCs) offer a promising alternative to internal combustion engines in road transport. During the last decade PEM FC research, development and demonstration (RD&D) activities have been steadily increasing worldwide, and targets have been set to begin their commercialisation in road transport by 2015–2020. However, there still is considerable uncertainty on whether these targets will actually be met. The picture is complex and market and technology issues are closely interlinked; investment in RD&D projects is essential but not sufficient; the development of suitable early markets is also necessary and policy is set to play an important role. Auxiliary power units (APUs) are generally regarded as one important early market for FCs in transport. This paper analyses the possible future market for diesel PEM FC APUs onboard long-haul trucks and its implications for the development of PEM FCs in general. The analysis, part of the project HyTRAN (EC Contract no. 502577), is aided by the use of a dynamic simulation model of technology and markets developed by the author. Results suggest that an interesting window of opportunity for diesel PEM FC APUs exists but this is subject to additional research particularly targeted at the rapid development of fuel processors.