Thermodynamic analysis of a solid oxide fuel cell jet hybrid engine for long-endurance unmanned air vehicles

Abstract

The turbine-less jet engine is promising due to the compressor driven by a motor and the high combustor exit temperature. It is a key problem that how to provide electric power for the motor. In this paper, a novel solid oxide fuel cell (SOFC) jet hybrid engine with anode and cathode recirculation is proposed and investigated where the SOFC power system is instead of the turbine to provide power for the compressor. For the system, compressed air entering into SOFC cathode channel is preheated by cathode recirculation exhaust. The gases reform in the reformer, which are air, fuel and steam from the anode recirculation exhaust. Reformed gases are provided for the SOFC anode channel. SOFC produces electric power to drive the compressor by a motor. Then, SOFC exhaust enters the combustor. The combustor exhaust expands and produces propulsion power in the nozzle. In order to evaluate and improve the performance of the SOFC jet hybrid engine, the thermodynamic analysis model is built. The energy and exergy analysis are accomplished. The effect of pressure ratio and flight altitude on the performance of the hybrid engine are studied. In addition, sensitivity analysis is accomplished. The preliminary results are as follows: (1) The thermal efficiency, the specific thrust and the specific impulse of the engine could reach to 57.60%, 790.00 N/(kg⋅s−1) and 4132 s under design conditions. (2) The sum of the relative exergy destruction ratio of the SOFC, the combustor, the nozzle and the exhaust is over 85%. (3) The total pressure recovery coefficient of the SOFC has a strong influence on the performance of the SOFC jet hybrid engine.