Thermodynamic analysis of recuperative gas turbines and aero engines

In the current work, the thermodynamic cycle of a conventional recuperative aero engine, in which a heat exchanger is placed after the power turbine, is compared with the thermodynamic cycles of two non-conventional recuperative aero engine configurations. For each configuration, different heat exchanger designs were used, all having the same core arrangement as the heat exchanger in the conventional recuperation aero engine which was designed by MTU aero engines AG and has been initially used in the first concept of the Intercooled Recuperative Aero engine of MTU. The core of the heat exchangers is specially designed to enhance heat transfer and minimize pressure losses when used as a recuperator in aero engines. Regarding the non-conventional cycle configurations, the first one is referred to as 'alternative recuperative' cycle, where a heat exchanger is placed between the high pressure and the power turbine, while the second one is referred to as 'staged heat recovery' where two heat exchangers are employed, one between the high and power turbines and the second one at the exhaust, downstream the power turbine. The comparison is based on the efficiencies and the thrust specific fuel consumption of each thermodynamic cycle. The performance characteristics of the heat exchangers were defined from previous experimental measurements and computational fluid dynamics. For all the examined configurations, the aero engine geometrical constrains were taken into consideration, especially for the alternative recuperative cycle. The results of the study showed that the alternative recuperative and the staged heat recovery cycles were more efficient than the conventional recuperative cycle for a specific range of pressure ratios and heat exchangers characteristics. These cycles combined with appropriate geometrical adaptations and with advanced, temperature resistant ceramics, alloys and other materials have the potential to further optimize the waste heat management exploitation in aero engines.