Hybrid Electric Propulsion

Abstract

Electrified propulsion holds the promise of reducing aviation’s CO2 emissions footprint through three means: access to green grid electric energy, improvements in aircraft performance through new airframe and propulsion system architectures and enabling further optimization of the gas turbine cycle. Charging an aircraft battery pack with green electric energy and using this energy to drive electric propulsors results in a zero emissions vehicle. This is practical for light aircraft and short missions. Boosting a Jet-A burning gas turbine with green electric energy (again stored in a ground charged battery), in either a parallel or series turbo-electric architecture can yield a net reduction in CO2 emissions, as long as the fuel burn required to carry the weight of a discharged battery pack does not overcome the reduction in fuel burn afforded by the ground charged battery. Several studies have indicated that a net savings is possible with cell level energy densities approach ∼ 500 whr/kg, a reasonable target for the 2030 time frame. Electrified propulsion can also enable unique aircraft configurations, employing a veryhigh efficiency prime mover (gas turbine) designed for running only a generator at peak efficiency, and/or distributing the propulsors throughout the aircraft, for improvement in L/D and propulsive efficiency.