The Thermal Efficiency of Free Piston Gas Turbines

Abstract

The free piston gas turbine will be classified into several cycles by the method of heating the compressed air, the fundamental cycles of wich are Pescara, constant pressure combustion, regeneration and regenerative constant pressure combustion cycle. By analysing the reversible air cycles of them thermodynamically, the relations among thermal efficiency and principal factors were obtained. The thermal efficiency of the three cycles except Pescara can be determined by the three factors, namely, thermal efficiency of engine cylinder, pressure ratio in compressor cylinder and ratio of turbine inlet temperature to the atmospheric one. While the efficiency of Pescara cycle can be determined only by arbitrary two factors among them and is equal to that of a Sabathe cycle which has the same max. pressure, degree of explosion and cut-off ratio as the engine cylinder of Pescara and operates on the atmospheric pressure. Assuming that the efficiency of engine cylinder is equal to 60% and the ratio of turbine inlet temperature to the atmospheric one 3, the max. thermal efficiency and the pressure ratio for each cycle were calculated as follows : [table]