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Design point analysis of a hybrid fuel cell gas turbine cycle for advanced distributed propulsion systems

Abstract:

The performance benefits of boundary layer ingestion in the case of air vehicles powered by distributed propulsors have been documented and explored extensively in numerous studies. Therefore, it is well known that increased inlet flow distortion and associated pressure losses due to boundary layer ingestion (BLI) can dramatically reduce these benefits. Additionally the high power required by the distributed propulsors implies large electrical components for generation and transmission which compromise the possible configurations for TeDP systems with BLI. In order to reduce the aforementioned aerodynamic integration aspects and the high power demands of TeDP systems alternative configurations which split he thrust between the propulsor unit and the turbofans have been investigated. In this work the potential benefits and challenges that an alternative thermodynamic cycle based on an hybrid gas turbine with SOFC’s implemented in an optimum TeDP system with BLI using thrust split is assessed. For this preliminary analysis simplified parametric models for fuel cells, gas turbines and weight have been used to capture important trends in the implementation of this cycle. The results obtained at design point conditions has shown that the implementation of this cycle and the use of liquid hydrogen for fuel and coolant could contribute to reduce by 70 % the TSFC before iterating and resizing. However, as main challenges for the implementation of this system arise hydrogen storage issues and the weight increment of the propulsion system due to the use of fuel cells. This latter parameter was observed to increase by 40 % before iterating and resizing. Furthermore, it was found that the use of thrust split could be beneficial to find an optimum configuration which presents a trade-off between the TSFC reduction and weight increment. Finally, it has been found that the synergistic advantages of the hybrid Brayton cycle and fuel cells with the TeDP system may offer opportunities for the performance improvement of the whole propulsion system.