Automakers are looking at electric motors as a replacement for the internal-combustion engine (ICE). Fuel cells have emerged as the more viable energy source than batteries. Especially PEMFCs are widely regarded as the technology of choice for automotive propulsion. PEMFCs run at about the temperature of boiling water and need a separate reformer to break down liquid fuels such as methanol and gasoline into hydrogen gas of suitable purity. The reformers tend to be large and complex, but economics is a much bigger obstacle to their commercialization, because internal-combustion engines are highly refined and relatively inexpensive to build per unit of power delivered. A parallel trend in automotive design is car electrification. Engine-driven 14-V-alternators providing onboard electrical power are being pushed to practical limits. Evolving dual-voltage 42/14-V systems based on the 42-V PowerNet specification will help meet the added power demands. This is where fuel cells come in, say Delphi Automotive Systems, Troy, Mich., and partner, German automaker BMW. Delphi's prototype solid-oxide fuel cell (SOFC) auxiliary power unit (APU) is sized to generate 5 kW of electrical power at 42 Vdc. The APU will replace alternators and work with the ICE on or off. The SOFC will provide electrical power for cars with conventional ICE drivetrains as well as for hybrid vehicles that join electric motors with small ICEs. SOFCs are highly efficient (> 50% fuel-to-electric conversion efficiency). They are compatible with conventional hydrocarbon fuels such as gasoline, methanol, natural gas, and diesel fuel, when combined with a relatively simple partial-oxidation reformer. SOFCs make electricity from fuel and oxidant gases in an electrochemical process that takes place across an ion-conducting, ceramic membrane. Reformed fuel (reformate) feeds to an anode, and air to a cathode. A solid electrolyte separates the two electrodes. Delphi's latest Generation 3 planar-type 30-cell stacks are designed to operate at about 750 deg C. They use separator plates and interconnects made of a special alloy called Cro Fer 22 APU, which is characterized by a small thermal expansion coefficient and the ability to remain electrically conductive at temperatures to 900 deg C. The APU's catalytic partial-oxidation reformer turns liquid fuel into small droplets, heats them, then catalytically converts the stream primarily into gaseous CO and H2, and less than a percent each of methane, ethylene, and ethane. Generation 2 tubular reformers in cyclic tests reach a steady-state output of about 20% H2 gas in under 3 min from startup. These systems are managed by an electronic control unit. In operation, an increase in electrical load signals the controller to boost flow rates of reformed fuel and air. Feedback comes from exhaust-gas analyzers and temperature and pressure sensors. The control system resides in the same package as the reformer and SOFC stacks. This makes it necessary to separate the package into two basic zones: an insulated hot-zone module, which houses the fuel-cell stack, the reformer, and a waste-energy recovery (WER) system, and a plant-support module, which houses the electronic-control unit, sensors, and actuators along with an electric blower fan that supplies air to the stack cathode, purging, and cooling systems. A 40-V lithium-ion battery operates the automobile electrical accessories when the SOFC is coming up to temperature, and supplies power to the cathode air blower, SOFC sensors and actuators during startup and cool down. The DOE performance objectives are not reached yet. A recent test of a Generation 3 30-cell stack produced a stack power density of 308 mW/cm², considerably less than the DOE target of > 1 W/cm². DOE projections say the SOFC portion of the APU should reach its operating temperature range of 600 to 800 deg C in under 2 min. Generation 2 stacks, for reference, take about 45 min. Shrinking APU size and weight are equally important objectives. For comparison, a Generation 2 APU consumes 60 liters and weighs 154 lb (70 kg). Ongoing work on Generation 3 APUs aims to further lower these numbers. Generation 3 stacks consume a volume of just 3.5 liters and weigh 28.6 lb (13 kg), a significant improvement over earlier Generation 2 stacks (6 liters and > 20 kg). Meanwhile, a BMW 7 Series fitted with a prototype APU is undergoing testing. Delphi says the APU's primary target is luxury cars with a high electrical demand, which represents about 1 to 2% of the vehicle market. The technology could also work in conventional super-ultra-low emissions vehicles (SULEVs), ships, portable, and stationary power systems.