Determination of the safe operation zone for a turbine-less and solid oxide fuel cell hybrid electric jet engine on unmanned aerial vehicles

Abstract

Solid oxide fuel cell (SOFC) hybrid electric jet engines without turbines in which compressors are powered by fuel cells instead of the turbines are promising and developmental aero-engines for unmanned aerial vehicles. The hybrid electric jet engine combines the merits of turbo-electric engines and fuel cell engines. To avoid component malfunctions and engine performance deterioration, the determination of the safe operation zone is necessary. In this study, a performance analysis model of the hybrid electric jet engine is built and the main conclusions are as follows. The safe operating zone of the hybrid engine is not restricted by turbine inlet temperature. Under low fuel flow rate and low air flow rate, zones of too low reforming temperature or too low SOFC open voltage exist. An unbalanced energy zone exists under high fuel flow rate and low air flow rate. The power produced by the SOFC is above that consumed by the compressor. The lower boundary of the safe zone is determined by the choke zone of the compressors. In the safe zone, the hybrid engine has properties of high specific thrust (837.6 N/(kg.s−1)) and high thermal efficiency (70.4%) at high fuel low and air flow rate.