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Fuel cell system models are key tools for automotive fuel cell system engineers to properly size components to meet design parameters without compromising efficiency by over-sizing parasitic components. A transient fuel cell system-level model is being developed that includes a simplified transient thermal and parasitics model. Model validation is achieved using a small 1.2 kW fuel cell system due to its availability. While this is a relatively small stack compared to a full size automotive stack, the power, general thermal behavior, and compressor parasitics portions of the model can be scaled to any number of cells with any size membrane area. With flexibility in membrane size and cell numbers, this model can be easily scaled to match full automotive stacks of any size. The electrochemical model employs a generalized polarization curve to approximate system performance and efficiency parameters needed for the other components of the model.

Proton exchange membrane (PEM) fuel cells are considered to be one of the best alternative power sources for automobiles. For this application, high power and high power density are required. Pressurizing the fuel cell system gives both higher efficiency and higher power density, but that pressure costs a percentage of the fuel cell output power. The compressor used to elevate the pressure has a direct effect on the system efficiency and water balance characteristics, especially at low load. Compressors being developed for fuel cell applications are examined to determine their effect on a fuel cell system. Two compressor technologies are discussed; a positive displacement twin-screw compressor and a turbocompressor, and their effects at low loads and set minimum compressor flows are examined. The turbocompressor proves to be a superior machine in terms of efficiency, and therefore offers the most promising effect on system efficiency of the two compressors.

Proton exchange membrane (PEM) fuel cells are considered to be one of the best alternative power sources for automobiles. For this application, high power and high power density are required. Pressurizing the fuel cell system gives both higher efficiency and higher power density, but that pressure costs a percentage of the fuel cell output power. The compressor used to elevate the pressure has a direct effect on the system efficiency and water balance characteristics, especially at low load. Compressors being developed for fuel cell applications are examined to determine their effect on a fuel cell system. Two compressor technologies are discussed; a positive displacement twin-screw compressor and a turbocompressor, along with their effects on overall system characteristics and efficiency. The turbocompressor proves to be a superior machine in terms of efficiency, and therefore offers the most promising effect on system efficiency of the two compressors.