The electrification of the ground vehicles propulsion is already happening at a bigger scale in the global car market and it is starting to expand to the military ground vehicles as well. The aircraft industry’s propulsion is currently dominated by conventional jet-propulsion but the electrification and more specifically the Distributed Electric Propulsion (DEP) open a new opportunity for the hybrid-electric propulsion for aviation emulating the increasing momentum in ground vehicle applications.
The greater flexibility of employing electric motors in aviation propulsion having a range extender as the source of energy can facilitate revolutionary aircraft architecture with greater engine-airframe integration, such as blended wing body, distributed electric propulsion and boundary layer ingestion propulsion systems. These new designs could substantially improve the overall aerodynamic efficiency of the airframe, further reducing the energy required to carry a given payload for a given mission.
Fully-electric aviation could potentially eliminate emissions, but thus far the application of electrified propulsion technologies has been restricted to relatively smaller and shorter-range aircrafts due to the limited specific energy of current batteries (e.g. 250 Wh/kg) and batteries that are currently under development (e.g. 500 Wh/kg). For comparison, these levels are an order of magnitude lower than that of the carbon-based fuel, which has a specific energy of >12,000 Wh/kg. In a recent study, NASA concluded that minimum requirement for full electric general aviation aircraft energy storage system is 2000 Wh/kg. Results of a modeling study showed that for a full-electric aircraft, there is no battery, even when considering advanced battery concepts, that can provide competitive payloads and flight ranges with the state-of-the art propulsion systems such as turbine or internal combustion engines (ice). It should also be noted that charging batteries on the ground is likely to increase aircraft turnaround times, and hence decreasing their economic viability and passengers’ convenience.
The Wankel engine has the unique feature of being a truly multi-fuel engine running seamlessly on a variety of known fossil-based fuels such as DF2, JP8, Jet A, Gasoline, etc. Carbon Neutral Liquid Fuels (CNLFs) such as Ethanol, Synfuel, Bio-LNG, etc. and gaseous fuels such as Hydrogen, NG and others.
Pairing advanced Wankel engines, such as the 350 and 500 Series engines’, that offer multi-fuel and high-power density features with equally power-dense, high-efficiency Permanent Magnet Generator (PMG) technology enables taking advantage of both technologies’ scalability and modularity. This allows the building of a family of highly compact, light-weight range extenders in the 25-250 kW range.
Using the Wankel range extenders or other ICE equally versatile engine technology in tandem with PMG generator/motor advanced features very attractive hybrid-electric drive train solutions can be achieved enhancing the ground vehicle design for efficient, safe missions.
Employing range-extender centric Distributed Electric Propulsion (DEP) technology for aircraft propulsion facilitates the proliferation of revolutionary aircraft architectures with increased versatility and multi-fuel efficiency.