Cycle Analysis of Gas Turbine / Solid Oxide Fuel Cell Hybrids for Aircraft

Turbine-fuel cell hybrids offer the potential to reduce fuel burn over direct turbogenerators in all-electric aircraft. However, understanding how to configure them optimally for a particular vehicle and mission is difficult because the need to represent both the gas turbine and fuel cell accurately results in models that are complex and slow. It also makes it hard to develop an understanding of the basic trades that drive design generally. This paper presents a simplified analytical model of the hybrid thermodynamic cycle that is computationally efficient and thus suitable for performing design trade studies in aircraft. It is demonstrated on a B737 class aircraft where it is used to assess the effects of design choices like cycle pressure ratio and the turbogenerator/fuel cell power split on basic vehicle performance parameters like range and fuel burn. Key findings are that the hybrid system can reduce fuel burn by ~20% and that the 'breakeven' performance of the reformer/fuel cell element (the performance needed to realize the reduction in fuel burn with no reduction in payload or range) is ~1kW/kg. Further improvement in reformer/fuel cell specific power will increase payload and range relative to the baseline vehicle.