Hydrogen-fueled Solid Oxide Fuel Cell - Gas Turbine (SOFC-GT) hybrid engines for aircraft propulsion: Comprehensive thermodynamic heat integration study

Developing sustainable aircraft propulsion requires considering both ecological and economic factors. One promising approach to reducing emissions and improving the efficiency of aircraft propulsion systems is integrating solid oxide fuel cells (SOFCs) into gas turbine cycles. A critical design challenge is air-side heat integration to ensure proper SOFC operating conditions and effective utilization of waste heat. This study evaluates four high-temperature heat-integration strategies employing exhaust gases from the SOFC, combustion chamber, high-pressure turbine, or low-pressure turbine. Parameter studies are performed for an aircraft in the ATR-72 power class considering variations in pressure ratio, SOFC fuel utilization, and current density. System performance is assessed in terms of efficiency, defined as shaft power output relative to the chemical energy of the supplied fuel, and the number of SOFC cells required to meet power demand, which serves as a preliminary weight indicator. The results show that preheating with low-pressure turbine exhaust achieves the highest efficiency (69.0%), while SOFC exhaust recuperation offers lower efficiency (63.4%) but requires smaller heat exchangers. Additionally, higher turbine inlet temperatures, enabled by additional fuel injection, reduce the required number of SOFC cells by up to an order of magnitude. These results demonstrate the trade-off between efficiency and the number of cells as an initial indicator of the weight of SOFC–gas turbine systems. • Hydrogen-fueled SOFC–GT hybrids for aircraft propulsion. • Four high-temperature heat-integration strategies compared. • Parameter study of pressure ratio, fuel utilization, and current density. • Efficiency vs. SOFC cell count trade-off investigated.