GTT, a subsidiary of Siemens Power Corporation, started in 2004 the EOS Project (Energy from Solid Oxides) with Politecnico of Torino, an applied research activity in Stationary Fuel Cells based on SOFC technology. The project (2004-2009) has the purpose to test a pilot plant for Combined Heat and Power. The operation of a SOFC generator is strictly affected by some regulation variables, among which there are the air stoichiometry and pre-heating temperature: sensitivity tests have been performed and are analyzed in the paper to characterize the single sector operation in a 100 kWe SOFC stack. In the experimental domain of air stoichiometry (4.6-4.8) and air pre-heating temperature (609-612°C), it is shown that air stoichiometry has a deeper contribution to the behavior of the stack. Its effect is linked essentially to the modification of the temperature distribution inside the generator. In the experimental domain, the generator voltage can be expressed as a linear function of the air stoichiometry, so that the voltage sensitivity to the air stoichiometry has been outlined for single generator sectors of the whole generator. In particular, the results of the experimental session suggest that different sensitivities can be associated with the position of the sectors in the stack arrangement. Moreover, it is observed that air stoichiometry sensitivity tests can provide useful information about the assessment and problems of thermal management and temperature distribution inside the SOFC generator: this can be an interesting tool to address the optimal design of a air supply system and distribution inside the generator. Finally, the correlation between the voltage and temperature sensitivity to the air stoichiometry have been discussed.

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