Thermodynamic Analysis of Solid Oxide Fuel Cell Gas Turbine Hybrid System for Aircraft Power Generation

Gas turbine technology has traditionally been used by the aviation industry for powering the aircraft including acting as APU. Operational unmanned aerial vehicle (UAV) has a gas turbine which is used as Auxiliary Power Unit (APU) which generically have overall efficiency not exceeding 35% which limits the range in terms of time in the air for the same APU fuel carried onboard. Gas turbine exhaust heat energy is largely wasted and there is scope of its utilization by thermally coupling it with a solid-oxide fuel cell (SOFC). By coupling SOFC with the gas turbine (GT) based power system, a hybrid SOFC-GT based APU system has been proposed for thermodynamic analysis, and the thermal efficiency of the proposed system can be enhanced by 77%. This paper focuses on a thermodynamic cycle analysis of an internal reformed solid oxide fuel cell which is integrated with the gas turbine to form a hybrid APU system for an UAV. Thermodynamic 1st and 2nd law, parametric analysis has been carried out, and the effect of various parameters such as compressor pressure ratio, turbine inlet temperature, air flow rate of the proposed system has been examined. From energy and exergy analysis of the proposed cycle, the thermodynamic losses within each cycle component have been evaluated which helps in estimating the work potentials of the fluid streams as well as heat interactions. Moreover, on increasing the air flow rate, the exergy destruction within SOFC decreases linearly while in the combustor, exergy destruction increases linearly. The overall cycle efficiency achievable by this hybrid cycle is observed to be around 62% significantly higher than tradition gas turbine based system. Auxiliary Power Unit of the future UAV’s may be designed around the proposed hybrid cycle which would lead to these units to deliver longer time in the air for the same fuel payload.