According to Delphi, the best way for fuel cells to enter the automotive market is through the trunk as an auxiliary power unit. There it can run on the engine's fuel supply and meet electrical power needs on the go, or while stopped, without trying to eliminate the internal combustion engine overnight.
Getting the last bit of a fuel system's hydrocarbon vapor under control demands adequate volume and little flow restriction. A honeycombed activated charcoal monolith traps the vapor in its structure, but readily releases them when manifold vacuum is applied.
Although many companies (including Delphi Automotive) are developing fuel cells to propel vehicles, Delphi is taking a less direct route toward acceptance of this technology. By leveraging expertise used in the production of oxygen sensors, spark plugs, and catalytic converters, Delphi plans to produce solid oxide fuel cells (SOFCs) as auxiliary power units (APUs) for luxury vehicles, work trucks, military vehicles, and over-the-road trucks in the latter half of this decade.
"OEMs are recognizing the benefits of powering accessories with the power off, or driving accessories that can't be run by the standard power generation system," says Jim Zizelman, chief engineer of Delphi's Advanced Engine Management Systems and Fuel Cells Division. Relying on an alternator driven by the engine "would not allow power-off use of the accessories, and wouldn't be as efficient–especially at idle when power reserves would have to be drawn from the battery," he says.
In production, the SOFC unit is expected to weigh 10 kg and displace 10 liters per kilowatt of output. So a 5-kW unit –about what the Delphi folk would expect for a premium luxury vehicle with all the trimmings–would weigh 50 kg and displace 50 liters. It would be located in the trunk, and run off the same fuel supply as the engine. "The reformer takes conventional fuels like gas, diesel, or methanol and converts it into a gas that is usable by the fuel cell," says Zizelman, "with very low emissions and very high efficiency." Still, it seems as though there is a future in propulsion for the SOFC APUs. "We aren't going to try and drive a hybrid vehicle using a fuel cell instead of a battery pack," says Jim Grieve, chief scientist at Delphi's Advanced Engine Management Systems and Fuel Cells Division. "However, it could be used as a small generator to extend range on electric vehicles," says Grieve, "giving them an almost unlimited range. Or you could run the fuel cell and vehicle engine together in a hybrid application. Plus, there's ‘combined cycle' power generation where the engine runs off the byproduct of the fuel cell." Each application mentioned either uses some form of electric drive, or requires changes to the fuel requirements and emission strategies of current engines. This is why Grieve and Zizelman insist the APU, not propulsion, will be the first outing for SOFC technology.
Carbon Canisters to the Rescue?
Even though emission standards continue to tighten, the established technology–an internal combustion engine and mechanical drive–survives. Sometimes the technology that allows this to happen is complex, other times it's quite simple. Delphi's carbon canister technology falls into the latter category.
If you sectioned Delphi's carbon canister vertically, you'd find, "a honeycombed activated carbon monolith that catches lower temperature hydrocarbon molecules, wrapped in a nylon container," says Matt Sheline, chief engineer for Delphi's Fuel Handling and Evaporative Emissions Systems Division. Which makes it sound like the large evaporative base canisters currently in use. So why invent a new version?
Two reasons. First, the California Air Resources Board (CARB) has two tough standards coming, LEV2 and PZEV. The first allows just two grams of hydrocarbon evaporation from the fuel system over three days. The PZEV standard, which stands for Partial Zero Emissions Vehicle and adds zero evaporative emissions to the already stringent Super Ultra-Low Emissions Vehicle (SULEV) standards, is a way for automakers to get partial electric vehicle credits. Second, onboard vapor recovery systems need to be low restriction to allow quick refueling. Multiple base canisters would seriously lengthen refueling stops by greatly increasing backpressure. Packaging, says Sue LaBine, staff design engineering manager, isn't a concern. "We have a couple of different scrubber sizes, from a 50-cc to a 200-cc unit, depending on the vehicle need. The bigger one, with SAE quick connectors at each end, is about 300 mm long and 80 mm in diameter." LaBine also says the unit can be used to bring marginal vehicles into compliance with current evaporative emission rules. And the cost? "About $15-$25 to the OEM," says Sheline.