F2008-06-089
Study on the Diagnosis of Vehicle PEM Fuel Cell Membrane Drying and Water Flooding
Membrane drying and water flooding are important problems concerned Proton Exchange Membrane Fuel Cell (PEMFC) system´s performance and reliability. In order to monitor the PEMFC stack´s drying and flooding, a cell voltage monitor system (CVMS) was attached on PEMFC system, which in return degraded the system´s stability and increased the system´s complexity. This paper´s purpose is to abandon the CVMS and diagnose PEMFC stack´s drying with in-situ ohmic resistance test and diagnose PEMFC´s flooding with anode pressure drop test. Firstly, the ohmic resistance were tested under variable operating conditions with current interruption method; the operating parameters´ influences to the ohmic resistance were analyzed, the results indicated that, the PEMFC´s ohmic resistance decrease along with the increase of the operating temperature and the cathode inlet relative humidity, the cathode inlet relative humidity, the stoichiometric ratios and the operating pressure influence the ohmic resistance not too much. After the PEMFC performance´s decay, its ohmic resistance increased over 10% in average. The PEMFC´s membrane drying processes were studied through the experimental method, the change rules of operating voltage, ohmic resistance and anode pressure drop had been obtained. Combined with the normal working PEMFC ohmic resistance´s neural network model, the in-situ ohmic resistance test plan had been discussed to judge if the PEMFC is working under the dryness condition. Secondly, the flooding experiments had been developed on the same PEMFC stack. The experiment result revealed that, the anode pressure drop data maintained good linear relations with the operational parameter in unflooding situations; the anode pressure drop obviously increased when flooding occured. In the flooding process, the operating voltage reduced continuously, the anode pressure drop would be stable after an increase. The operational parameters influenced the PEMFC´s flooding: increasing the cathode inlet relative humidity, elevating the operating temperature, enhancing the operating current, reducing the cathode inlet stoichiometric ratio, the PEMFC would flood easily. But the anode inlet stoichiometric ratio and operating pressure did not have the obvious influence to PEMFC´s flooding. The PEMFC´s flooding problem would be solved effectively by pulse exhaust method. It would improve the PEMFC´s performance and increase its efficiency to choose the proper pulse opportunity and pulse width. Through this study, the PEMFC´s ohmic resistance test for membrane drying diagnosis and anode pressure drop test for PEMFC flooding diagnosis system had been established, an in-situ diagnosis system for vehicle PEMFC water management system have been raised. The work in this paper basically dealt with the main problems in the PEMFC water management system for vehicular application. It is valuable for optimizing PEMFC system and improving PEMFC´s efficiency.
Session: Hydrogen