Semester

Summer

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Powsiri Klinkhachorn.

Abstract

The PEM (Polymer Electrolyte Membrane) fuel cell is a promising technology for mobile applications because of its compactness, low operating temperature, and quick startup time. The following study evaluates the efficiency of convection type PEM fuel cells by conducting a series of tests on two commercially available fuel cells, and examines each fuel cell's control methods to identify the key factors for the each cell's fuel and air management. The control system affects the stack by purging a dead-ended stack, which stabilizes the performance of the fuel cell by periodically purging the system of contaminants or water building up in the system and maintains the input hydrogen pressure; and the fan speed, which controls the temperature and helps pull air into the stack. The purging system was determined to have a large part in maintaining the performance of the fuel cell over time, with the fuel cell's output consistently deteriorating over time if kept dead-ended. Purging too often also had the effects of wasting hydrogen and unbalancing the internal pressures of the fuel cell. It was determined that the period between purges was most effective when dependent on the power drawn from the fuel cell and the rate of the fuel cell's voltage drop.;By observing the performance of two similar PEM fuel cells, the Jadoo and Horizon 100W fuel cells, the efficiency of their control systems could be compared and evaluated. The Jadoo purging system worked most efficiently at loads between 40-70W, which appeared to be the time when the fan was used to introduce the most sufficient amount of air into the stack and the purging period was 20 minutes. The average practical efficiency of the 100W-rated fuel cell was 42%, while the peak practical efficiency 48% at 62W. When run at higher power outputs that required more frequent purging, there was a small decline in the efficiency; and the fuel cell's lowest efficiency occurred when run at the low power outputs of 20W or less when most of the power from the fuel cell was diverted to the control unit. The Horizon fuel cell was purged whenever the voltage had dropped below a certain threshold, and had an overall average efficiency of 34% reaching higher efficiencies when run at lower power outputs. Its highest measured efficiency peaked at 48% at 11W, which was when the fuel cell required the lowest purging frequency. Models of the Jadoo PEM fuel cell were developed in the MATLAB/SIMULINK environment using the experimental data that incorporated the effects of keeping stack dead-ended.

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