Delphi, Global Shift Paradigm ...Battery & EV Technology January 2001
The fuel-cell team at Delphi (5725 Delphi Dr., Troy, MI 48098; Tel: 248/813-2000, Fax: 248/813-2523) along with Global Thermoelectric, are building a proof-of-concept unit to demonstrate the advantages of a solid oxide fuel cell (SOFC) combined with a battery to serve as an auxiliary power unit (APU) for autos and trucks.
The SOFC APU provides a paradigm shift in the supply of electric power to passenger cars. This is consistent with the increasing power demands in automobiles in this era of more comfort and safety.
A small SOFC system for auxiliary power can be used as a high-efficiency generator that runs with the engine on or off. In this sense, it is not a threat to the internal combustion engine and does not have to reach the extremely low cost per kilowatt needed for propulsion. It is tolerant of carbon monoxide, which it can use as a fuel, and has less sensitivity to contaminants such as sulfur and light hydrocarbons in reformed fuel. It can be applied to conventional or mild hybrid configurations and is not linked to a fully electric drive train.
The overall system can be broken down into several subsystems, each with a specific function toward the overall operation: SOFC stack system; fuel reformer system (microreformer and main reformer); thermal management system; waste energy recovery sys-tem; process air system, SOFC control system, and power electronics system; and lithium polymer battery pack.
Delphi is developing a gasoline, partial oxidation (POX) reformer for fueling the SOFC stack. The fuel reformer is housed inside the hot box and operates at high temperatures. The reformers are fed fuel and air through valves located in the main plenum chamber. The fuel is introduced through the insulated way via an injector. The air is introduced with air control valves, and is fed from the main plenum chamber. Reformer operation is monitored with temperature sensors, gas pressure sensors, and gas composition sensors. Integration of the POX reformer with a SOFC stack has been successfully demonstrated. Current work is focused on developing automated controls.
Delphi and Global Thermoelectric are developing the system to meet the stringent volume, weight, and thermal cycling restrictions imposed by the auto industry. The stacks are made of planar metallic interconnects, 10-cm by 10-cm cells, compressible high-temperature seals, and stack compression and gas delivery elements.
The stacks have been sized for the automotive voltage requirements (42-v) and power outputs (2-5 kW). The stack
configuration consists of four 15-cell or 27-cell modules mounted on a gas-delivery manifold. The modules are then electrically connected in the appropriate manner to achieve the 42-v requirement.
One of the benefits of the modular assembly is the ability to condition- monitor the smaller stacks and, if required, swap out a module rather than having to disassemble a complete stack system. The modular approach also adds flexibility to the layout of the system, allowing for numerous stack configurations to fit the customer's space availability. Flow management is simplified by the modular arrangement, using short flow paths versus the long chambers of larger stacks.
Power is sent from the SOFC stack to the power electronics system controllers and the lithium polymer battery pack. From there power goes to the systems within the car, including heating and air conditioning.
Current and future work is focused on reducing the cost for commercialization, improving system power density, improving fuel use, achieving fast start-up of the system, and achieving automotive levels of durability over usage and thermal cycles.
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