Abstract
Purpose In recent years, increased awareness on global warming effects led to a renewed interest in all kinds of green technologies. Among them, some attention has been devoted to hybrid-electric aircraft – aircraft where the propulsion system contains power systems driven by electricity and power systems driven by hydrocarbon-based fuel. Examples of these systems include electric motors and gas turbines, respectively. Despite the fact that several research groups have tried to design such aircraft, in a way, it can actually save fuel with respect to conventional designs, the results hardly approach the required fuel savings to justify a new design. One possible path to improve these designs is to optimize the onboard energy management, in other words, when to use fuel and when to use stored electricity during a mission. The purpose of this paper is to address the topic of energy management applied to hybrid-electric aircraft, including its relevance for the conceptual design of aircraft and present a practical example of optimal energy management. Design/methodology/approach To address this problem the dynamic programming (DP) method for optimal control problems was used and, together with an aircraft performance model, an optimal energy management was obtained for a given aircraft flying a given trajectory. Findings The results show how the energy onboard a hybrid fuel-battery aircraft can be optimally managed during the mission. The optimal results were compared with non-optimal result, and small differences were found. A large sensitivity of the results to the battery charging efficiency was also found. Originality/value The novelty of this work comes from the application of DP for energy management to a variable weight system which includes energy recovery via a propeller.
Highlights
In the past decades, the trend towards “More Electric Aircraft” has materialized in new airliners such as the Boeing 787
The optimal results will be compared with a non-optimal energy management, and conclusions will be drawn
The hybrid aircraft performance will be compared with the conventional aircraft, and results regarding the mesh convergence study will be presented
Summary
The trend towards “More Electric Aircraft” has materialized in new airliners such as the Boeing 787. One possible future evolution for this trend is electric propulsion: the use of electricity available onboard to power the propulsion system This opens new possibilities for aircraft design, such as distributed electric propulsion or radically new aircraft configurations (Sehra and Whitlow, 2004; Gohardani et al, 2011). The results of these exercises indicate only marginal improvements in fuel efficiency when hybrid electric designs are compared against conventional propulsion designs. These marginal improvements are conditionally dependent on the future evolution of battery energy density. Aircraft manufacturers are not able to finance the development cost of a new aircraft unless it delivers substantial reductions in fuel consumption
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