Rafal Marcin Laskowski, Janusz Lewandowski


In the present paper, the performance of a simple-cycle gas turbine was analysed. The first part of the paper focuses on the performance of a gas turbine stage. Assuming the working medium to be an ideal gas, a relation between the current and maximum enthalpy and entropy changes was obtained. Based on this relation, three other relations were obtained: between stage internal efficiency, current and maximum enthalpy and entropy changes, and stage inlet temperature. A relation for stage outlet temperature under changed conditions, taking into account reference conditions, was also proposed. The proposed relations are true when the difference between the inlet and outlet pressures is small, as is the case with the gas turbine stage. In the second part of the paper, determining optimal compression ratio for the whole simple-cycle gas turbine system is described. Most commonly, the optimal compression ratio is assumed for maximum power or thermal efficiency of the whole system. The optimal compression ratio for maximum power is determined analytically, while the one for maximum efficiency iteratively. In the paper, an analytical relation for the optimal compression for maximum thermal efficiency was presented. In order to determine the optimal compression ratio for a simple-cycle gas turbine, the applicability of another function was examined; besides the enthalpy changes for the turbine and compressor, the other function also directly takes into account entropy changes in the turbine and compressor. In the discussion, identical properties of air and flue gas were assumed, pressure losses in the system were neglected, and the air and flue gas mass flow rates were assumed to be equal.


efficiency, gas turbine, optimal compression ratio

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