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In addition to high-profile fuel cell applications such as automotive propulsion and distributed power generation, the use of fuel cells as auxiliary power units (APU) for vehicles has received considerable attention. APU applications may be an attractive market because fuel cells offer some attractive features for APU applications and the APU market offers a true mass-market opportunity that does not require some of the challenging performance and cost targets required for propulsion systems for vehicles. In this paper we discuss the technical performance requirements for PEM and SOFC APUs, as well as the current status of the technology and the implications for fuel cell system configuration and cost.

The transportation sector in the United States is a major contributor to global energy consumption and carbon dioxide emission. To assess the future potentials of different technologies in addressing these two issues, we used a family of simulation programs to predict fuel consumption for passenger cars in 2020. The selected technology combinations that have good market potential and could be in mass production include: advanced gasoline and diesel internal combustion engine vehicles with automatically-shifting clutched transmissions, gasoline, diesel, and compressed natural gas hybrid electric vehicles with continuously variable transmissions, direct hydrogen, gasoline and methanol reformer fuel cell hybrid electric vehicles with direct ratio drive, and battery electric vehicle with direct ratio drive.

Cost is one of the critical factors in the commercialization of PEM fuel cells in automotive markets. Arthur D. Little has been working with the U.S. Department of Energy, Office of Transportation Technologies to assess the cost of fuel-flexible reformer proton exchange membrane (PEM) fuel cell systems based on near-term technology but cost modeled at high production volumes and to assess future technology scenarios. Integral to this effort has been the development of a system configuration (in conjunction with Argonne National Laboratories), specification of performance parameters and catalyst requirements, development of representative component designs and manufacturing processes for these components, and development of a comprehensive bill of materials and list of purchased components. The model, data, and component designs have been refined based on comments from the Freedom Car Technical Team and fuel cell system and component developers.

One of the biggest barriers to commercialization of fuel cell vehicles is the high cost of materials and manufacturing of fuel cell components. Precious metal materials in the membrane electrode assemblies (MEAs) account for more than 17 percent of the total cost of polymer electrolyte membrane (PEM) fuel cell systems. Precious metals such as platinum may also be required for fuel processing catalysts. The Department of Energy (DOE) is addressing the important issue of the cost of fuel cell components by supporting R&D projects aimed at improving the performance of fuel cells which would lead to reduced platinum loading, as well as developing low-cost automated industrial processes for the manufacture of electrodes and MEAs. Other projects include development of a supply-demand elasticity model. The long term reserves and availability of platinum is a serious issue facing the commercial viability of fuel cell vehicles.

After about a decade of considerable investments in polymer electrolyte fuel cell (PEMFC) and in solid oxide fuel cell (SOFC) technology, both are being actively considered for vehicle applications. The two vehicle applications being most actively considered for fuel cells are propulsion (mainly for PEMFC) and auxiliary power (for both PEMFC and SOFC). For all transportation applications, fuel cells promise the benefits of clean and quiet operation, potentially low maintenance and high efficiency, and ultimately greater utility to drivers and passengers. Initial system and vehicle prototypes have started to demonstrate some of these benefits, but much technology development is still needed before commercialization can occur. Not surprisingly then, there are serious hurdles to be overcome if fuel cells are to become true competitors for internal combustion engines (ICEs) in automotive applications.

The solid oxide fuel cell (SOFC) system has emerged as an important technology for automotive and stationary applications. Modeling and simulation of the SOFC system have been utilized as an integral tool in an accelerated joint SOFC system development program. Development of unique modeling approaches and their results are discussed and compared with experimental performance. One dimensional system level analysis using Aspen with an embedded stack electrochemical model was performed resulting in effective sub-system partitioning and requirements definition. Further, a three-dimensional integrated electrochemical / thermal / computational fluid dynamics analysis of steady-state operation was employed. The combination of one-dimensional and three-dimensional environments led to effective performance projection at all levels in the system, resulting in optimization of overall system performance early in the design cycle.

Delphi Automotive Systems and BMW are jointly developing Solid Oxide Fuel Cell (SOFC) technology for application in the transportation industry primarily as an on-board Auxiliary Power Unit (APU). In the first application of this joint program, the APU will be used to power an electric air conditioning system without the need for operating the vehicle engine. The SOFC based APU technology has the potential to provide a paradigm shift in the supply of electric power for passenger cars. Furthermore, by supplementing the conventional fuel with reformate in the internal combustion engine, extremely low emissions and high system efficiencies are possible. This is consistent with the increasing power demands in automobiles in the new era of more comfort and safety along with environmental friendliness. Delphi Automotive Systems and BMW were successful in demonstrating an Auxiliary Power Unit (APU) based on Solid Oxide Fuel Cell (SOFC) technology in February, 2001.

Arthur D. Little in conjunction with the Department of Energy and the Illinois Department of Commerce and Community Affairs are developing an ethanol fuel processor for fuel cell vehicles. Initial studies were carried out on a 25 kWe catalytic partial oxidation (POX) reformer to determine the effect of equivalence ratio, steam to carbon ratio, and residence time on ethanol conversion. Results of the POX experiments show near equilibrium yields of hydrogen and carbon monoxide for an equivalence ratio of 3.0 with a fuel processor efficiency of 80%. The size and weight of the prototype reformer yield power densities of 1.44 l/kW and 1.74 kg/kW at an estimated cost of $20/kW.

Industrial grade ethanol, in concentrations ranging from 130 proof to 200 proof, can be used as a feedstock for a 50kWe advanced fuel processor developed by Arthur D. Little, Inc. for fuel cell vehicles. At 180 proof concentration, hydrated ethanol showed no performance degradation compared with both 200 proof (pure) ethanol and E95 (95% ethanol and 5% gasoline) at equivalence ratios ranging from 3.0 to 4.0. Environmental benefits associated with the use of ethanol in fuel cell power systems include its production from renewable biological sources, low toxicity in the event of an accidental spill, and recycling of carbon dioxide released by the process back to the plant matter used as ethanol feedstock. Cost savings associated with the use of hydrated ethanol are expected to include lower production costs, lower distribution costs, and lower powerplant costs due to the possibility of system simplification.

Fuel cells show great promise in generating electrical power for a variety of uses. In the automotive realm, one focus has been on the use of fuel cells for primary vehicle propulsion. Another emerging application is the fuel cell as the primary provider of electrical power to the vehicle, augmenting or replacing the traditional alternator, while producing higher power levels. The advantage of the fuel cell in this role is that the fuel cell operation is de-coupled from that of the engine. High power levels can be achieved independent of engine speed and power can be produced without the engine running. This paper examines the application of a fuel cell auxiliary power unit (APU) to a dual-voltage 42V/14V automotive electrical system meeting the evolving 42V PowerNet specifications. An architecture for this electrical system is presented, followed by a sizing analysis to properly match the fuel cell stack to the voltage of the PowerNet and to a 42V battery pack.

Delphi Automotive Systems and BMW have been jointly developing Solid Oxide Fuel Cell (SOFC) technology for application in the transportation industry primarily as an on-board Auxiliary Power Unit (APU). In the first application of this joint program, the APU will be used to power an electric air conditioning system without the need for operating the vehicle engine. The SOFC-based APU technology has the potential to provide a paradigm shift in the supply of electric power for passenger cars. Furthermore, supplementing the conventional fuel with reformate in the internal combustion engine, extremely low emissions and high system efficiencies are possible. This is consistent with the increasing power demands in automobiles in the new era of more comfort and safety along with environmental friendliness.

While it is generally agreed that the PEM fuel cell technology is best for road vehicles, the need for a source of relatively pure hydrogen poses significant challenges. There are two distinct options that are currently being considered: On-board processing of gasoline or methanol Fueling with hydrogen gas made in an off-board facility Each option has different implications for the fueling infrastructure and for the technologies required both on- and off-board the vehicle. In addition, various fueling strategies shift the balance of risk between fuel providers and vehicle manufacturers. Generally speaking, alternative fueling options can be seen to trade off technical risk (e.g., will it work?) for commercial risk (e.g., will anyone buy it?). In seeking a satisfactory business solution, a key issue is the balance between these two risks on the part of the vehicle manufacturer and the fuel provider.