jueves, 13 de mayo de 2010

GM Highlights Engineering Advances With Second-Generation Fuel Cell System and Fifth-Generation Stack; Poised for Production Around 2015

28 September 2009

The second generation hydrogen fuel cell system under development by General Motors—which contains its fifth-generation fuel cell stack—is half the size, 220 pounds (100 kg) lighter and uses less than half the platinum (30 grams plus or minus vs. 80 grams) of the current generation in the Chevrolet Equinox Fuel Cell electric vehicle (earlier post).

The production-intent fuel cell system can be packaged under the hood in about the same space as a four-cylinder engine; by contrast, the first generation system in the Equinox (with the fourth-generation stack) is about the size of a file cabinet, says Charles Freese, executive director of GM Fuel Cell Activities.
Gm2genfcs2
The first generation fuel cell system (with fourth-generation stack technology) used in the Equinox. The new second-generation system is to the left. Click to enlarge.

The new system, where we have adopted a pretty radical change in the architecture itself, downsizes dramatically, takes 100 kg of the mass out, and takes the size down to half of that of the Equinox. What constitutes the propulsion system architecture is not just the fuel cell stack and the balance of plant, it’s also the traction motor—which is mounted to the base [of the stack]—and the power electronics unit. The system looks about like a small inline gasoline engine, you could even put it into a sedan. It’s pretty tightly packaged and integrated.

In 2007, GM took fuel cell development activity out of R&D and moved it over to GM Powertrain, along with 500 scientists and engineers. (Earlier post.) Work that has been going on since then has been less focused on just the stack itself, and more on the mass production at low cost of fuel cell system, said Freese.

As an example of the type of production-oriented engineering optimization GM is taking, Freese used the injection system.

If you go back to the first-generation system in the Equinox, it uses a complex hydrogen injection system: 7 injectors with flow shift units, its oscillates the hydrogen back and forth through the cell. It had its own plumbing and control module. We’ve replaced that with an injector the size of my little finger. It does the whole job.

When you see the cell itself, you go from these composite carbon cell plates that are more difficult to manufacture and maybe less robust in terms of assembly damage. We’ve moved to a stamped steel plate—something like you make for the head gasket on an engine.

The second-generation system uses 320 cells that provide the same functionality as the 400-cell system used in the Equinox, Freese said. The air compressor operates at 120,000 rpm and has a 5-liter dimension. By contrast, the Equinox system operates at 80,000 rpm and has a volume of about 9 liters. “It’s all about taking things, making them smaller, integrating them,” said Freese.

Packaging of the system plays a role too. Parts have been moved around from where they are on the Equinox, Freese said, allowing GM to get rid of some of the cables in that system. In addition to the system-level work, GM has made advances with its stack technology. The electrode design is different, Freese said, enabling a significant change in platinum loading.

We’re in the 80 gram platinum level on the Equinox. The Gen 2 architecture is basically down to a 30 gram plus or minus platinum loading, and we are working toward a sub-10 gram platinum level. We have a clear roadmap established. If we look at the Gen 2 architecture as commercialized in the 2015 time frame, we’re looking at the sub-10 level sometime in the 2018-2022 time frame.

At or below the 10 grams level, Freese said, the fuel cell system would use less platinum than current catalytic converters for combustion engines.

Commercialization. GM has not yet announced the vehicle that the second-generation design will go into for its first tests; however, Freese noted that the fuel cell technology works very well in the family-size vehicles. For an Equinox, for example, roughly 123 kW of energy is required to move the vehicle, according to Freese. The current Equinox fuel cell vehicle uses as stack that produces 93 kW.

A system off of a Gen 2 architecture to fit into the same vehicle would be around 87 kW...we strike a balance between the battery and the fuel cell.

While continuing to develop technical improvements to the basic fuel cell system, GM is focused on steps toward commercializing the technology. Freese, who prior to his role with fuel cells was executive director for GM’s diesel engines, noted a number of similarities in the development of propulsion systems.

A lot of the way that we develop technologies for production are the same, no matter what kind of propulsion system. What surprised me were not the things I thought. I find similarities in so many areas with developing a diesel powertrain. [What surprised me] were the things I didn’t anticipate until getting into it.

In terms of the similarities, you think of some of the technologies on board. We faced challenges in injection systems and noise. Those are common problems on diesel powertrains. The challenges that you have to overcome are very similar. Another area is the turbo on the diesel or the compressor on the fuel cell. You are moving air and using a rotating compressor...it’s very similar. As you look at the design, you can find part after part that uses things that use similar tools, you develop test them, prove that they are ready for production. You really can draw across the disciplines.

GM, says Freese, is developing the second generation system on a 2015 timeframe. The company is currently in the pre-development phase, and is roughly a little over a year before making a development commitment.

GM has invested more than $1.5 billion in fuel cell technology and we are committed to continuing to invest, but we no longer can go it alone. As we approach a costly part of the program, we will require government and industry partnerships to install a hydrogen infrastructure and help create a customer pull for the products.

Charles Freese

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