Fuel Cells: Coming Down to Earth

Attention manufacturers of internal combustion engines: Although it is still way too early to become inordinately concerned, Chrysler Corp. engineers have developed what one of them, Christopher E. Borroni-Bird, advanced technologies specialist, describes as “the gold standard” for automotive fuel cell technologies, and he calls for
the world’s automakers to devote their fuel cell development activities along the lines that Chrysler has drawn.

The reason: Whereas work is being done by other manufacturers on creating fuel cells that are powered by hydrogen or methane, the Chrysler approach utilizes gasoline (or methane or diesel fuel or alcohol). There is a substantial gas station infrastructure (according to Francois Castaing, Chrysler’s executive vp in charge of Powertrain and International Operations, “There’s $200-billion invested in the way gasoline is distributed”), and that’s unlikely to change anytime soon. So Chrysler says, in effect, “Why fight what exists on the street corners across America?”

A fuel cell isn’t a container. Rather, it is actually a system that produces electricity that can be used to drive an electric traction drive motor, which can be used to propel a vehicle. The electricity is generated by a chemical reaction between hydrogen—extracted from gasoline—and oxygen—available from the atmosphere. A platinum catalyst triggers the reaction.


The Processing.

To simplify the way it works: The gasoline goes from the fuel tank to a vaporizer that, through the use of heat, transforms the liquid to a gas. The vapor then goes to a partial oxidation (POX) reactor. Here, the vapor is mixed with air. There’s a spark from a plug, and the result is hydrogen, carbon monoxide and hydrogen sulfide. The hydrogen sulfide is undesirable, so the sulfur is filtered out of the gas. Carbon monoxide isn’t good for the fuel cells (to say nothing of people). So the next step is a water-gas shift. Here, steam is introduced into a canister where the carbon monoxide is being held. Copper oxide and zinc oxide catalysts come into play and the combination of the various elements results in carbon dioxide and hydrogen. There’s a bit of the carbon monoxide remaining in this hydrogen-rich gas, about 10,000 parts per million (ppm), that’s still way too much, so it is onto the PROX—preferential oxidation stage. At this stage, air is injected into the gas and when the oxygen encounters the carbon monoxide over a platinum catalyst, the primary result is carbon dioxide and less than 10 ppm of carbon monoxide. This results in the fuel.

The fuel then goes to a fuel cell stack. This stack, as configured for a full-sized car (think of a Chrysler Concorde, for example), is about 8 in. in diameter and 60 in. long. It is located where a drive shaft is ordinarily located. Within the fuel cell modules in the stack electricity is generated through a chemical reaction between the hydrogen generated and available oxygen in the presence of a platinum catalyst. Given that a fuel cell module generates under 1 volt and that it takes from about 20 to 50 kW for acceptable vehicle performance (0 to 60 mph in under seven seconds and have a travel range of about 400 miles), there are hundreds of modules in a given stack.


Some Implications.

So what are some of the implications? First of all, the fuel cell approach certainly changes the components that need to be manufactured. There are fewer moving parts than are used in internal combustion engines.

Canisters are a big part of the new system. Based on the current design, there’s a canister 6 in. in diameter and 20-in. long for the burner/vaporizer; a 14-in. diameter, 22-in. long canister for the POX fuel processor; another canister about the same size as the burner/vaporizer for the steam and air-injection process. In addition, there are a need for a small air compressor (1 ft. in diameter and 1 ft. long) and a coolant radiator (about the same size as a conventional unit). So think canisters, valves and pipes, not cylinders, pistons and manifolds.

Chrysler is working with Arthur D. Little on the project. It is expected that there will be a demonstration vehicle in two years and production prototypes in 10 years or less.