Future propulsion and integration:
towards a hybrid/electric aircraft
- Aligning commercial aviation with the COP21's target: ΔT < 2°C
- Critical need for disruptive technologies beyond incremental technology improvements
- Developing hybrid-electric propulsion and integration technologies
- Developing a roadmap for key enabling technologies
Why Hybrid Electric
Fully electric aircraft would be an appealing solution to eliminate CO2 emissions. However, building a fully electric commercial aircraft would require a step beyond the highest battery performance anticipated in a predictable future (densities in the range from 500 to 600 Wh/kg are beyond current R&D effort, while more than 750 Wh/kg would be needed for a B737 to transport 150 PAX over 900 nm).
Partial electrification through hybridisation, mixing electric and thermal engines and energy sources, is an intermediate step offering extended degrees of freedom for optimising the aircraft performance and reduce the fossil block fuel consumption. A variety of concepts can be envisaged with different kinds of hybrid propulsion architectures.
A broad variety of concepts and architectures:
- Parallel hybrid electric may be used to provide electric boosts from batteries to thermal engines during parts of the flight, allowing to optimise gas turbine performances throughout the mission profile, and in particular for cruise.
- Electricity production on board the aircraft with turboelectric architecture opens the way to distributed electric propulsion, which allows to implement innovative propulsion integration to develop synergetic effect with the airframe.
- Blowing the wing in order to increase lift at low speed and optimally size the wing for cruise (e.g. NASA X-57);
- Increasing effective by-pass ratio (BPR, which increases propulsive efficiency) and reducing individual propulsor diameter (this facilitates integration of propulsion with high BPR)
- Boundary-layer-ingestion (BLI e.g. in CENTRELINE project)
- Additional use of propulsion for example for control (removing or reducing empennages).
- Multiple variants may be envisaged mixing batteries and turbo-generators, leading to series hybrid architectures, which can be combined with the above mentioned integration of the propulsion system (e.g. batteries can be used to absorb peaks of energy demand or to power engines during some phases of the flight).