GCTool Computer Model Helps Focus Fuel Cell Vehicle Research

Somewhere near Detroit, an automotive engineer stares at the ceiling, wondering how to squeeze 1% more efficiency out of the fuel cell reformer she's been working on. Never mind 5% more from the next component on her list. Computer software, such as Argonne's GCTool, lets designers "try out" different system configurations, without the expense and delays of actually building numerous prototypes. Our engineer could learn that she's been worrying about the wrong thing.

Argonne systems analysts have shown that in fuel cell systems for vehicles, more is not always better. For example, increasing the efficiency of the fuel processor (the component that converts hydrocarbon fuel into hydrogen for the fuel cell) may actually lower the overall system efficiency. "They go in opposite directions. You can make the fuel processor more efficient, but that's because you're stealing energy from somewhere else in the system," says Argonne's Romesh Kumar, who leads Argonne's fuel cell modeling efforts.

Modular, Flexible, and Easy to Use

These results, along with other surprising findings, have been obtained by using the General Computational toolkit (GCtool), a versatile simulation software package developed by Argonne for designing, analyzing, and comparing different power-plant configurations. This flexible software uses a modular approach to integrate many of the detailed thermodynamic and component models developed during decades of fuel cell and power system research at Argonne and elsewhere.

GCtool is easy to use. "An entire fuel cell system - everything necessary to go from fuel to electricity - is specified as a sequence of lines of simple code," Kumar says. From this input, the software generates a system schematic, and users can switch between the input window and the diagram until they are satisfied with the flows. According to Kumar, "You enter lines in the input window and then you look at the diagram and say, 'Oh wait a minute - this isn't going where I wanted,' so you go back and change it."

All the input, including lines specifying the fuel, feed rates, and component performance, can fit on one page for a relatively simple system. Users can modify all the system inputs - down to the density and thickness of a heat exchanger wall, if desired. After a simulation run, the schematic displays all the input and output values for each component. The calculated results, including the iterations conducted to achieve convergence, are written to the output file to any desired level of detail.

Analyses Reveal Surprises

Using GCTool for sensitivity analyses can save automotive engineers a tremendous amount of time. Kumar explains: "We might see that a small difference in the fuel cell performance yields a big difference in the vehicle efficiency, which means the whole system is very sensitive to that. Whereas if we change the airflow by a factor of two, the efficiency may not change much - then we can say the system isn't much affected by the airflow and we can focus our efforts elsewhere."

By questioning all of their assumptions, Argonne's systems analysis team found another surprise hiding in the compressor/expander systems used to manage water and operating pressure in fuel cell systems - namely, that the efficiency of these systems is much more important to overall efficiency than expected.

GCTool Saves Time and Money

As automotive fuel cell technology gets closer to what promises to be a huge market, companies are naturally reluctant to reveal their research. The kind of analysis done at Argonne, because it can be made public, provides an important forum for discussion that can keep developers from working in isolation and spending energy, time, and money that could be devoted to more critical problems.

A variety of arrangements are available for licensing the technology. About a dozen organizations outside of Argonne are using GCtool for systems analysis and evaluation. Some of these users are private-sector fuel cell companies and universities that assist the U.S. Department of Energy (DOE) in developing new fuel processing and fuel cell system technologies for automotive applications.

Research for GCtool is supported by funding from DOE's Office of Energy Efficiency and Renewable Energy.