Publications

Despite the substantially lower energy per unit mass of batteries compared to hydrocarbon fuels, electrification of the aircraft propulsion system could lead to increases in energy efficiency for certain types of missions. This work builds on the electric powertrain component models (battery, converter, motor) from previous work and presents models for the propulsor, power distribution system, thermal management system (TMS), and wiring in order to complete an all- electric propulsion system framework. This framework is used to simulate a propulsion system with power loads representative of a commuter aircraft mission that transports 19 passengers over 100 nmi. Results show that the battery makes up over 60% of the total propulsion system mass, indicating that improvements in battery technology are essential to lower propulsion system mass. Despite making up a smaller fraction of the propulsion system mass, the other components impact the overall system via their efficiency since that sizes the battery and the TMS. Distributed propulsion is found to lower the propulsion system mass, with diminishing returns beyond 10 propulsors due to the increased heat rejection and hence TMS mass.

Electrification of the aircraft propulsion system has the potential to decrease the flight energy requirement, by leveraging higher component efficiencies as well as distributed propulsion and boundary layer ingestion. Previous results have shown an energy-usage benefit for small all- electric aircraft over conventional aircraft, but the benefit is highly sensitive to the underlying technology-level and modeling assumptions. This work presents models for the components of an all-electric propulsion system (battery, converter, motor) at a fidelity level that captures their operational behavior under the variable-power loads of the different flight segments. They are integrated into an all-electric propulsion powertrain sized for a commuter aircraft mission carrying 19 passengers over 100 nmi, as well as for the NASA X-57 Maxwell mission. Results using these higher-fidelity models predict a heavier propulsion system that consumes more energy than what is obtained from low-fidelity models with a constant-power, cruise- only representation of the mission. Motors and converters, sized for the maximum power requirements in a mission, show differences in efficiencies even across lower-power segments. Resulting system voltages are found to be well beyond currently certifiable limits. Distributed propulsion helps brings system voltages down with a small powertrain efficiency penalty, but increases the mass of the powertrain components.

The current work presents a sizing and optimization framework that uses a power-based analysis to model transport aircraft with varying degrees of electrification. This framework uses a unified propulsion system model that represents the wide variety of conventional and electrified propulsion system architectures through just one source and one load electrification parameter. The framework is applied to a commuter mission for aircraft carrying up to 19 passengers, and the effects of electrification analyzed based on on-board energy requirements with three different levels of electrical component technology. Results show that energy usage benefits of electrification depend strongly on the assumed technology levels. With today’s state-of-the-art batteries and electrical components, electrification is unlikely to prove beneficial. However, with significant technological improvements – in particular for batteries – electrification could substantially reduce energy needs. For a 463 km (250 nmi) mission, an all-electric architecture reduces energy consumption by up to 69% based on our optimistic 2035 technology assumptions. Hybrid-electric configurations can retain a significant proportion of the benefit of electrification while increasing the feasible mission range: for an extended range of 926 km (500 nmi), an aircraft storing 90% of its energy in batteries and 10% in fuel could reduce energy consumption by as much as 63% for the optimistic technology assumptions, and as much as 27% with more realistic 2035 technology values. Furthermore, we find that technologies enabled by electrification, specifically distributed propulsion and boundary layer ingestion, could play an important role in facilitating electrification, although to a lesser degree than the other technological advances.

This paper presents a body-force propulsor model that replaces the engine blades with a source volume to produce the equivalent flow turning, work input, and losses. The motivation for developing this model is to capture the effects of inlet flow non-uniformity on propulsor performance, while using a local formulation appropriate for full-aircraft CFD at a computational cost compatible with design studies. The model is able to capture non-axisymmetric effects and only requires specification of the blade camber and thickness distributions. An inviscid formulation for the body-force was previously found to be capable of predicting the inviscid distortion transfer effects, but losses and blade metal blockage effects were not accounted for. An improved formulation with a blockage component is proposed here and is shown to properly predict the propulsor work. Loss terms are included to model 2D profile losses and secondary flow losses. The proposed model is implemented in the flow solver ADflow and validated against NASA rotor 67 experimental data. The total pressure ratio shows good agreement and the choking mass flow was captured within a 1% error. The isentropic efficiency and its off-design trends were qualitatively well predicted.

The goal of this paper is to determine whether an open rotor aircraft configuration has the potential to provide fuel-burn benefits relative to a conventional turbofan aircraft, and if so in which regions of the payload-range design space adopting an open rotor technology would be most advantageous. A design space exploration focused on the major trends and design drivers is carried out for open rotor aircraft with aft mounted and wing mounted engines, and their performance compared to a turbofan baseline. We consider transport aircraft with ranges between 1 000 and 7 000 nautical miles and 50 to 400 passengers, and introduce a modeling approach for open rotor engines into a conceptual design and optimization framework. For each range-passenger requirement, aircraft are optimized for minimum fuel burn on an economic range mission. It is found that open rotor configurations are best suited for short range missions with large passenger counts, and that aft mounted open rotors outperform wing mounted ones. The optimum open rotor engine design sacrifices engine and aerodynamic efficiency in order to limit integration penalties and propulsion system weight.

This work presents a design space exploration for electrified aircraft that use electrical components for propulsion, and identifies configurations and missions for which electrification can provide an energy-usage advantage relative to hydrocarbon-based propulsion. A framework was developed to capture the major trade-offs of electrification at cruise condition, as well as the effects of distributed propulsion and boundary layer ingestion. The analysis is based on a parametric exploration of the trade-space with focus on mission size (payload and range) and technology level. It considers aircraft classes ranging from a 20-passenger thin-haul up to a twin-aisle intercontinental transport. All-electric aircraft are found to be best at low ranges (200–500,nmi), requiring the lowest amount of on-board energy but with a limited feasibility region. Turbo-electric architectures can be beneficial even with current technology, and are best for long missions. Adding a turbo-generator to an electric aircraft, for a hybrid-electric propulsion system, acts as a range extender and is optimal for intermediate-size missions. Finally, leveraging distributed propulsion and boundary layer ingestion improves energy efficiency and expands the range of feasible missions for highly electrified aircraft.