Sizing of fuel-based energy systems for electric aircraft

Abstract

Optimized electric motors are lighter and smaller than conventional piston engines. As a result, new airplane configurations are feasible as motors can be placed in unconventional positions. Through careful aircraft design higher aerodynamic efficiencies of airframe, propeller, and propeller integration can be achieved. The energy density of current batteries, however, still limits strongly the range of purely battery powered aircraft. But if the energy is stored in liquid fuel and converted by a generator into electric energy, then the advantages of electric propelled airplanes and conventional combustion engines can be combined. But which combustion engine is optimal for such a serial-hybrid electric aircraft? In this new propulsion chain, other boundary conditions apply to the combustion engine than in conventional aircraft designs. These boundary conditions interact with the characteristics of combustion engines. An example for an engine characteristic is that different kinds of piston engines exist. It can be observed that technologies, which result in lighter piston engines, are associated with lower efficiencies and vice versa. In this paper it will be shown through considerations on aircraft level, that the optimal combustion engine for an electric-hybrid airplane should be heavier and more efficient than the optimal combustion engine for a conventional aircraft.

Multifunctional Composites for Future Energy Storage in Aerospace Structures

“…Various electric aircraft designs have been investigated [6,[45][46][47][48][49][50], either dealing with the conversion of existing fuel-powered aircrafts to all-electric or hybrid aircrafts, or with the development of totally new aircraft designs. However, many electric aircraft designs rely on substituting the fuel-powered propulsion system by an electrical one using, for example, (heavy) conventional batteries.…”

Competitiveness of Hybrid Electric Aircraft on Short Range Scheduled Flights

“…One of the critical enablers for hybrid aircraft is the advancement of lithium-ion batteries, providing higher energy density, power density, and increased levels of safety. Further, hybrid electric aircraft concepts make use of the increased degrees of freedom in the design space between aerodynamics, aeroelastics, structures, propulsion, and energy conversion, aiming to optimize the integration of the propulsive units and the energy management system for efficiency (Geiß & Voit-Nitschmann, 2017).…”

“…In this case, a hybrid system can size one single gas-turbine for cruise climb power and take the additionally required power for takeoff from the batteries, while the critical case of a one-engine-inoperative-go-around can be significantly alleviated by the use of multiple electric propulsive units. During cruise, the gas-turbine runs close to best efficiency (see Figure 1) and can even be further optimized to operate at that specific design point, drastically reducing the thrust-specific fuel consumption -in other words, fuel would be saved in these phases of flight (Liu, Valencia, &Teng, 2016 andGeiß &Voit-Nitschmann, 2017).…”

“…Additional power for peak demand scenarios, such as a singleengine-go-around, can be provided by the batteries. Since the gas-turbine would run at constant cruise power without the necessity for wide power variations, it could be optimized for that design point, which would enable significant improvements in fuel consumption (Liu, Valencia, &Teng, 2016 andGeiß &Voit-Nitschmann, 2017).…”

“…Thus, in hybrid applications, batteries would enable short periods of high power demand, such as takeoffs and go-arounds. Additional applications could include electric taxi exclusively from battery power to ensure zero emissions on the ground and increase efficiency: Turboprop engines and turbofans have relatively high fuel flow rates during taxi operations and reach a low point in specific fuel consumption (Geiß & Voit-Nitschmann, 2017). Especially in the case of busy airports, the amount of taxi fuel used due to long waiting periods at the departure holding point with idling engines is of concern to the operators.…”