Analysis of a gas turbine auxiliary power unit system based on a fuel cell combustor

In this study, a gas turbine (GT) system for auxiliary power units (APUs) is proposed based on a fuel cell combustor, which separates combustion into three processes: fuel-rich combustion, electrochemical reaction through solid oxide fuel cells (SOFCs), and fuel-lean combustion. Compared with the traditional GT system, the efficiency of the proposed system is much higher due to the high efficiency of the electrochemical conversion process in SOFCs. Meanwhile, the advantage of the GT's high power density is conserved to improve the system power density by increasing the GT power proportion, which makes it possible to be used as an APU for aircraft. First, the system was simulated and evaluated at the base case with electrical efficiency reaching 45.62% and power density reaching 0.43 kW/kg. Then, extra fuel was added into the fuel-lean combustion chamber to increase the GT power proportion, which led to an increase in power density and a decrease in efficiency. Finally, the concept of a superhigh-temperature SOFC was proposed to further increase the system power density. When the SOFCs operate at a superhigh temperature of 1473 K, the power density of the system reaches 2.67 kW/kg, which is much higher than that of conventional SOFC-GT hybrid systems.