Modeling Solid Oxide Fuel Cells for Hybrid-Electric Turbo Generators in Aircraft Applications

Abstract

Air travel accounts for a significant portion of domestic and global greenhouse gas emissions. Decarbonized electric propulsion has the potential to be disruptive to replace conventional gas turbine based engines and could be an attractive solution to reduce aircraft emissions. This work aims to design a pressurized hybrid solid oxide fuel cell/gas turbine turbo generator using carbon neutral liquid fuels for narrow body commercial aircraft with high gravimetric power densities. Novel Ni/GDC based cell architectures are used to lower cell operating temperature and thereby, reduce both stack costs (e.g., interconnects and seals) and system balance-of-plant costs. There is currently limited understanding of the operating characteristics and optimum conditions for employing GDC based cells in these applications. Further, the mixed ion electronic conducting (MIEC) nature of GDC and its impact on cell voltage and electrochemical performance has yet to be quantified. This work presents a one-dimensional, down-the-channel stack model that captures physicochemical processes for an intermediate temperature Ni/GDC based fuel cell. The leakage current phenomena of MIEC anodes is captured by calculating open circuit voltage as a function of conductivity, temperature and pressure. Activation overpotentials are calculated based on published results in literature that fit exchange current densities and charge transfer coefficients based on experimental electrochemical impedance spectroscopy measurements [1,2]. Fickian diffusion for mass transport across the porous electrodes and rate mechanisms to evaluate reforming characteristics are used. The model predicts electrochemical performance for varying cell temperatures and flow rates. The distribution of overpotentials with cell temperature and current density is analyzed. Thermal management of power dense stack operating conditions is critical to understand. Thus, the stack model is also employed to within a subsystem where it is integrated with an autothermal reformer and anode gas recycle to parametrically assess operating conditions and performance, particularly towards minimizing cooling air flow requirements. Figure 1