Assessment of Engine and Vehicle Performance Using Integrated Hybrid-Electric Propulsion Models

NASA is actively funding research into advanced, unconventional aircraft and engine architectures to achieve drastic reductions in vehicle fuel burn, noise, and emissions. One such concept is being explored by The Boeing Company, the General Electric Company, Virginia Polytechnic Institute and State University, and the Georgia Institute of Technology under the Subsonic Ultra Green Aircraft Research Project. A major cornerstone of this research is evaluating the potential performance benefits that can be attributed to using hybrid-electric propulsion. Hybrid-electric propulsion in this context involves a non-Brayton power generation or storage source, such as a battery or a fuel cell that can be used to provide additional propulsive energy to a conventional Brayton-cycle-powered turbofan engine. This research constructs an integrated Numerical Propulsion System Simulation hybrid-electric propulsion model capable of predicting hybrid-electric engine performance throughout the operational envelope. The system consists of a battery-powered motor partially driving the low-pressure shaft of a conventional turbofan engine. The applied motor power adds an additional degree of freedom, along with power setting, available to the aircraft designer during mission analysis. Modeling features and issues unique to hybrid-electric propulsion systems are described, and a vehicle trade study is carried out to determine the optimum engine cycle for both a cryogenic and conventionally driven motor system.