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Hybrid-electric propulsion is recognized as an enabling technology for reducing aviation’s environmental impact. In this work, a serial/parallel hybrid configuration of a 19-passenger commuter aircraft is investigated. Two underwing-mounted turboprop engines are connected to electrical branches via generators. One rear fuselage-mounted electrically driven ducted fan is coupled with an electric motor and respective electrical branch. A battery system completes the selected architecture. Consistency in modeling accuracy of propulsion systems is aimed for by development of an integrated framework. A multipoint synthesis scheme for the gas turbine and electric fan is combined with physics-based analytical modeling for electrical components. Influence of turbomachinery and electrical power system design points on the integrated power system is examined. An opposing trend between electrical and conventional powertrain mass is driven by electric fan design power. Power system efficiency improvements in the order of 2% favor high-power electric fan designs. A trade-off in electrical power system mass and performance arises from oversizing of electrical components for load manipulation. Branch efficiency improvements of up to 3% imply potential to achieve battery mass reduction due to fewer transmission losses. A threshold system voltage of 1 kV, yielding 32% mass reduction of electrical branches and performance improvements of 1–2%, is identified. This work sets the foundation for interpreting mission-level electrification outcomes that are driven by interactions on the integrated power system. Areas of conflicting interests and synergistic opportunities are highlighted for optimal conceptual design of hybrid powertrains.

Aircraft electrification for propulsion is a promising way to alleviate the negative environmental impact of conventional carbon-powered aviation. Inclusion of the electrical powertrain aims to enhance design freedom, allowing for more efficient power systems and operational schemes. In this work, a design space exploration is performed, aiming to derive power management guidelines based on aircraft environmental performance. A 19-passenger commuter aircraft employing the series/parallel partial hybrid-electric architecture is examined. Two underwing-mounted turboprop engines are combined with a boundary layer ingestion fan mounted in the aft of the aircraft and powered by an electrical drive. The primary electrical energy source is a battery system. A multidisciplinary framework is utilized, comprising modeling approaches for multipoint thermal engine design, physics-based electrical component sizing and performance, aircraft sizing, mission design, and environmental assessment. The investigation revealed that the reference designed hybrid-electric configuration with entry-into-service (EIS) 2035 assumed technologies yields roughly 18% improvement in block consumption and emissions, but an 8% increase in maximum takeoff weight (MTOW), compared to its 2014 conventional counterpart. The design space exploration for an optimal power management scheme indicated a minimum average ratio of 1:1.35 between cruise and design point hybridization power. However, even the optimally operated hybrid aircraft showcases worse environmental performance compared to the conventional design of same entry-into-service date. The investigation has revealed that the complex powertrain and hybrid architecture selected may be more suitable for larger class aircraft, where aircraft requirements can be relaxed and higher degrees of electrification are not penalized or confined by set constraints.

Hybrid electric aviation is a possible step toward sustainable flight. Several hybrid architectures and synergetic concepts have been investigated. However, environmental performance results seem to be inconsistent due to deviations in technology assumptions and a mismatch between the fidelity of methodologies used for simulation of different aircraft systems. A multidisciplinary framework is developed, consisting of detailed modeling approaches for thermal and turbomachinery components, electrical power system design, aircraft/mission, and environmental analysis. The framework is employed for the investigation of an entry-into-service 2035 30 passenger commuter aircraft with a design mission of 1000 nautical miles. The investigation of parallel hybrid electric, turbo-electric, and series/parallel partial architectures is performed through a systematic conceptual design approach. The analysis reveals a bare minimum battery technology of 0.75 kWh/kg and 0.8 kW/kg, needed to compete with the conventional aircraft's performance. High degrees of hybridization (>20%) trigger the snowball effect of aircraft mass and thrust requirement, counteracting specific fuel and performance benefits generated by electrification. The turbo-electric and series/parallel partial concepts are paired with an electrically driven boundary layer ingestion fan. For those concepts to result in any block fuel and emissions benefits compared to conventional counterparts, a drag reduction from wake ingestion of 7.5–10% is required, with power split ratios between the electrically driven fan and propellers being limited to 15% due to extensive mass increase.

The aviation industry faces significant environmental challenges, prompting the implementation of regulations to mitigate the adverse effect of carbon-based energy and associated emissions. While electrified flight is a promising pathway, limitations in specific energy density of batteries narrow down the application space to commuter and regional classes. Towards that direction, this work investigates the design and operation of a series hybrid electric 30-passenger regional aircraft. A multi-disciplinary framework is utilized, comprising modelling approaches for multi-point thermal engine design, physics-based electrical component sizing and performance, aircraft sizing, mission design, and environmental assessment. Distributed propulsion with up to three propellers per wing is evaluated for aerodynamic benefits. With optimal wing redesign, drag reduction benefits only reach 1% for the selected aircraft class and flight velocities. Variable free power turbine speed operation is promising in reducing engine mass and improving performance of both thermal and electrical power systems. A combination of hybridization during take-off, climb and cruise defines the optimal design and operation guidelines for the hybrid concept. However, due to the increased mass of the battery and electrical power system, block fuel benefits only in the order of 5% are reported, compared to a turboelectric aircraft. When compared with a conventional configuration of same entry-into-service year, the series concept is outperformed in the examined range of battery assumed technologies.

Hydrogen for propulsion could lead the industry to achieving the set environmental goals. This work performs a comparative cycle and engine design for a hydrogen-fired and conventional Jet-A burning configuration. Aircraft design and mission performance complete the conceptual design loop. A 19-passenger small commuter aircraft is investigated. A multi-disciplinary framework is developed for the study. A multipoint synthesis scheme is employed for conventional, and hydrogen powered engine assessment. Cryogenic hydrogen tanks and a thermal management system are integrated in the aircraft and their volumetric and gravimetric impact are assessed showing an expected 13% increase of aircraft mass. Direct combustion of hydrogen leads to more efficient and smaller turboprop engines due to the increased specific heat capacity of combustion products. Engine cycle design reveals that the optimum aircraft energy consumption lies at an overall pressure ratio at cruise of 15 and a combustor outlet temperature of 1,400 K. However, the hydrogen tanks and fuel conditioning system increase aircraft mass sufficiently to offset the fuel conthe H2 and Jet-A configurations by 3-4%. This work reveals a lower bound of H2 fuel system gravimetric performance due to aircraft weight certification and highlights the design guidelines for the engine, aircraft, and storage system.