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Towards a Transformation to Sustainable Aviation Systems
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Towards a Transformation to Sustainable Aviation Systems

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A: Sustainable Energy".

Deadline for manuscript submissions: closed (31 July 2018) | Viewed by 150297

Special Issue Editors

Prof. Dr. Jens Friedrichs

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Guest Editor
Institute of Jet propulsion and Turbomachinery, Technical University of Braunschweig, Braunschweig, Germany
Interests: fan aerodynamics and design; propulsion integration; jet engine deterioration & maintenance; intake / fan interaction
Prof. Dr. Ulrike Krewer

E-Mail Website
Guest Editor
Institute of Energy and Process Systems Engineering, Technical University of Braunschweig, Braunschweig, Germany
Interests: fuel cells; batteries; energy systems; electrochemical processes; model-based and experimental system analysis; dynamics process systems
Prof. Dr. Peter Horst

E-Mail Website
Guest Editor
Institute of Aircraft Design and Lightweight Structures, Technical University of Braunschweig, Braunschweig, Germany
Interests: composites; fatigue; aeronautical engineering; XFEM; mechanical properties; materials engineering; aluminium; aircraft design
Prof. Dr. Thomas Spengler

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Guest Editor
Institute of Automotive Management and Industrial Production, Technical University of Braunschweig, 38106 Braunschweig, Germany
Interests: operations management in the steel industry; supply chain management; sustainability and circular economy
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Rolf Radespiel

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Guest Editor
Institute of Fluid Mechanics, Technical University of Braunschweig, Hermann-Blenk-Str. 37, 38108 Braunschweig, Germany
Interests: aerodynamics; computational fluid dynamics; heat transfer; fluid dynamics; fluid mechanics; turbulence modeling; numerical simulation; CFD simulation; turbulence; experimental fluid mechanics
Prof. Dr. Arno Kwade

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Guest Editor
Institute for Particle Technology, Technische Universität Braunschweig, Volkmaroder Str. 5, D-38104 Braunschweig, Germany
Interests: particle breakage; milling; dispersing and classification of particles; powder flow (characterization, equipment design); coating of particles; synthesis and formulation of nanoparticles; DEM-simulations (calibration, contact models); battery electrode production; drug product formulation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue shall cover scientific approaches and contributions to the transformation of aviation systems towards sustainability over the next few decades. This is motivated by expectations to reduce the environmental impact, and to improve the reliability, safety and on-schedule operation, of aviation. In other sectors of mobility, a reduction of the carbon footprint is being realized through intensive electrification; the very high power and energy density demand of aviation do not allow for a direct transfer of such technology. This Special Issue aims to give interdisciplinary insight into possible technologies for transformation to a sustainable aviation system, and, thus, should contribute in overcoming existing paradigms, allowing for new approaches in aircraft and subsystems. Concepts, technologies, and their impacts need to be understood and analyzed in detail to propose system solutions that satisfy the expectations and allow aviation to be part of a closed-looped or zero-emission energy system. Topics may cover research from the perspective of natural science, engineering, economics, and social science. Examples are new and hybrid energy systems, synthetic high-density liquid energy storage for aviation, fuel cells and batteries for aviation, electrification concepts, as well as flight physics and new aircraft system concepts, including economic and social aspects.

Prof. Dr. Jens Friedrichs
Prof. Dr. Ulrike Krewer
Prof. Dr. Peter Horst
Prof. Dr. Thomas Spengler
Prof. Dr. Rolf Radespiel
Prof. Dr. Arno Kwade
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Hybrid Energy Systems
  • Electrochemical and Carbon-free Energy Conversion
  • Aircraft Design and Sizing
  • Active Flow Control
  • Energy-Based Flight Physics
  • New and Integrated Propulsion Concepts
  • Lifecycle Costing and Assessment
  • Efficient Energy Conversion and Distribution
  • Cross-impact Analysis

Published Papers (16 papers)

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Research

15 pages, 1854 KiB  
Article
Modelling of A Boundary Layer Ingesting Propulsor
by Nils Budziszewski and Jens Friedrichs
Energies 2018, 11(4), 708; https://0-doi-org.brum.beds.ac.uk/10.3390/en11040708 - 21 Mar 2018
Cited by 27 | Viewed by 5317
Abstract
Boundary layer ingestion is a promising method to decrease the propulsive power consumption of an aircraft, and therefore the fuel consumption. This leads to a reduced environmental impact and an improved cost-efficiency. To get a better understanding of this method and to estimate [...] Read more.
Boundary layer ingestion is a promising method to decrease the propulsive power consumption of an aircraft, and therefore the fuel consumption. This leads to a reduced environmental impact and an improved cost-efficiency. To get a better understanding of this method and to estimate its benefits, the modelling of a propulsor located at the upper rear centerbody of a blended wing body aircraft is presented in this paper. A parallel compressor model approach is used to analyse the impact of the ingested low velocity fluid which leads to a non-uniform inflow. The required boundary layer data are generated with an analysis tool for 2D subsonic airfoils. Some parameter variations are conducted with the developed programme to study their impact on the power saving potential. In addition, a simple estimation for the benefit of embedded aeroengines is given. Despite the drawback from fan efficiency due to the inflow distortion, the results show a significant decrease in required propulsive power for boundary layer ingestion in combination with integrated engines. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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25 pages, 11481 KiB  
Article
Aircraft Noise Assessment—From Single Components to Large Scenarios
by Jan Delfs, Lothar Bertsch, Christoph Zellmann, Lennart Rossian, Ehsan Kian Far, Tobias Ring and Sabine C. Langer
Energies 2018, 11(2), 429; https://0-doi-org.brum.beds.ac.uk/10.3390/en11020429 - 13 Feb 2018
Cited by 13 | Viewed by 6920
Abstract
The strategic European paper “Flightpath 2050” claims dramatic reductions of noise for aviation transport scenarios in 2050: “...The perceived noise emission of flying aircraft is reduced by 65%. These are relative to the capabilities of typical new aircraft in 2000...”. There is a [...] Read more.
The strategic European paper “Flightpath 2050” claims dramatic reductions of noise for aviation transport scenarios in 2050: “...The perceived noise emission of flying aircraft is reduced by 65%. These are relative to the capabilities of typical new aircraft in 2000...”. There is a consensus among experts that these far reaching objectives cannot be accomplished by application of noise reduction technologies at the level of aircraft components only. Comparably drastic claims simultaneously expressed in Flightpath 2050 for carbon dioxide and NOX reduction underline the need for step changes in aircraft technologies and aircraft configurations. New aircraft concepts with entirely different propulsion concepts will emerge, including unconventional power supplies from renewable energy sources, ranging from electric over hybrid to synthetic fuels. Given this foreseen revolution in aircraft technology the question arises, how the noise impact of these new aircraft may be assessed. Within the present contribution, a multi-level, multi-fidelity approach is proposed which enables aircraft noise assessment. It is composed by coupling noise prediction methods at three different levels of detail. On the first level, high fidelity methods for predicting the aeroacoustic behavior of aircraft components (and installations) are required since in the early stages of the development of innovative noise reduction technology test data is not available. The results are transferred to the second level, where radiation patterns of entire conventional and future aircraft concepts are assembled and noise emissions for single aircraft are computed. In the third level, large scale scenarios with many aircraft are considered to accurately predict the noise exposure for receivers on the ground. It is shown that reasonable predictions of the ground noise exposure level may be obtained. Furthermore, even though simplifications and omissions are introduced, it is shown that the method is capable of transferring all relevant physical aspects through the levels. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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23 pages, 2732 KiB  
Article
A Study on Electrofuels in Aviation
by Andreas Goldmann, Waldemar Sauter, Marcel Oettinger, Tim Kluge, Uwe Schröder, Joerg R. Seume, Jens Friedrichs and Friedrich Dinkelacker
Energies 2018, 11(2), 392; https://0-doi-org.brum.beds.ac.uk/10.3390/en11020392 - 08 Feb 2018
Cited by 77 | Viewed by 13038
Abstract
With the growth of aviation traffic and the demand for emission reduction, alternative fuels like the so-called electrofuels could comprise a sustainable solution. Electrofuels are understood as those that use renewable energy for fuel synthesis and that are carbon-neutral with respect to greenhouse [...] Read more.
With the growth of aviation traffic and the demand for emission reduction, alternative fuels like the so-called electrofuels could comprise a sustainable solution. Electrofuels are understood as those that use renewable energy for fuel synthesis and that are carbon-neutral with respect to greenhouse gas emission. In this study, five potential electrofuels are discussed with respect to the potential application as aviation fuels, being n-octane, methanol, methane, hydrogen and ammonia, and compared to conventional Jet A-1 fuel. Three important aspects are illuminated. Firstly, the synthesis process of the electrofuel is described with its technological paths, its energy efficiency and the maturity or research need of the production. Secondly, the physico-chemical properties are compared with respect to specific energy, energy density, as well as those properties relevant to the combustion of the fuels, i.e., autoignition delay time, adiabatic flame temperature, laminar flame speed and extinction strain rate. Results show that the physical and combustion properties significantly differ from jet fuel, except for n-octane. The results describe how the different electrofuels perform with respect to important aspects such as fuel and air mass flow rates. In addition, the results help determine mixture properties of the exhaust gas for each electrofuel. Thirdly, a turbine configuration is investigated at a constant operating point to further analyze the drop-in potential of electrofuels in aircraft engines. It is found that electrofuels can generally substitute conventional kerosene-based fuels, but have some downsides in the form of higher structural loads and potentially lower efficiencies. Finally, a preliminary comparative evaluation matrix is developed. It contains specifically those fields for the different proposed electrofuels where special challenges and problematic points are seen that need more research for potential application. Synthetically-produced n-octane is seen as a potential candidate for a future electrofuel where even a drop-in capability is given. For the other fuels, more issues need further research to allow the application as electrofuels in aviation. Specifically interesting could be the combination of hydrogen with ammonia in the far future; however, the research is just at the beginning stage. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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21 pages, 10782 KiB  
Article
A Structural Design Concept for a Multi-Shell Blended Wing Body with Laminar Flow Control
by Majeed Bishara, Peter Horst, Hinesh Madhusoodanan, Martin Brod, Benedikt Daum and Raimund Rolfes
Energies 2018, 11(2), 383; https://0-doi-org.brum.beds.ac.uk/10.3390/en11020383 - 07 Feb 2018
Cited by 17 | Viewed by 6706
Abstract
Static and fatigue analyses are presented for a new blended wing body (BWB) fuselage concept considering laminar flow control (LFC) by boundary layer suction in order to reduce the aerodynamic drag. BWB aircraft design concepts profit from a structurally beneficial distribution of lift [...] Read more.
Static and fatigue analyses are presented for a new blended wing body (BWB) fuselage concept considering laminar flow control (LFC) by boundary layer suction in order to reduce the aerodynamic drag. BWB aircraft design concepts profit from a structurally beneficial distribution of lift and weight and allow a better utilization of interior space over conventional layouts. A structurally efficient design concept for the pressurized BWB cabin is a vaulted layout that is, however, aerodynamically disadvantageous. A suitable remedy is a multi-shell design concept with a separate outer skin. The synergetic combination of such a multi-shell BWB fuselage with a LFC via perforation of the outer skin to attain a drag reduction appears promising. In this work, two relevant structural design aspects are considered. First, a numerical model for a ribbed double-shell design of a fuselage segment is analyzed. Second, fatigue aspects of the perforation in the outer skin are investigated. A design making use of controlled fiber orientation is proposed for the perforated skin. The fatigue behavior is compared to perforation methods with conventional fiber topologies and to configurations without perforations. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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15 pages, 393 KiB  
Article
Analysis and Design of Fuel Cell Systems for Aviation
by Thomas Kadyk, Christopher Winnefeld, Richard Hanke-Rauschenbach and Ulrike Krewer
Energies 2018, 11(2), 375; https://0-doi-org.brum.beds.ac.uk/10.3390/en11020375 - 06 Feb 2018
Cited by 71 | Viewed by 12089
Abstract
In this paper, the design of fuel cells for the main energy supply of passenger transportation aircraft is discussed. Using a physical model of a fuel cell, general design considerations are derived. Considering different possible design objectives, the trade-off between power density and [...] Read more.
In this paper, the design of fuel cells for the main energy supply of passenger transportation aircraft is discussed. Using a physical model of a fuel cell, general design considerations are derived. Considering different possible design objectives, the trade-off between power density and efficiency is discussed. A universal cost–benefit curve is derived to aid the design process. A weight factor w P is introduced, which allows incorporating technical (e.g., system mass and efficiency) as well as non-technical design objectives (e.g., operating cost, emission goals, social acceptance or technology affinity, political factors). The optimal fuel cell design is not determined by the characteristics of the fuel cell alone, but also by the characteristics of the other system components. The fuel cell needs to be designed in the context of the whole energy system. This is demonstrated by combining the fuel cell model with simple and detailed design models of a liquid hydrogen tank. The presented methodology and models allows assessing the potential of fuel cell systems for mass reduction of future passenger aircraft. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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25 pages, 8037 KiB  
Article
Challenges and Opportunities of Very Light High-Performance Electric Drives for Aviation
by Markus Henke, Gerrit Narjes, Jan Hoffmann, Constantin Wohlers, Stefan Urbanek, Christian Heister, Jörn Steinbrink, Wolf-Rüdiger Canders and Bernd Ponick
Energies 2018, 11(2), 344; https://0-doi-org.brum.beds.ac.uk/10.3390/en11020344 - 02 Feb 2018
Cited by 58 | Viewed by 9427
Abstract
The demand for alternative fueling methods to reduce the need for fossil fuels is not limited to the electrification of ground vehicles. More-electric and all-electric aircraft pose challenges, with extensive requirements in terms of power density, efficiency, safety, and environmental sustainability. This paper [...] Read more.
The demand for alternative fueling methods to reduce the need for fossil fuels is not limited to the electrification of ground vehicles. More-electric and all-electric aircraft pose challenges, with extensive requirements in terms of power density, efficiency, safety, and environmental sustainability. This paper focuses on electrical machines and their components, especially for high-power applications like the main propulsion. The electrical machine is evaluated from different aspects, followed by a closer look at the components and materials to determine the suitability of the current standard materials and advanced technologies. Furthermore, the mechanical and thermal aspects are reviewed, including new and innovative concepts for the cooling of windings and for the use of additive manufacturing. Aircraft have special demands regarding weight and installation space. Following recent developments and looking ahead to the future, the need and the possibilities for light and efficient electrical machines are addressed. All of the approaches and developments presented lead to a better understanding of the challenges to be expected and highlight the upcoming opportunities in electrical machine design for the use of electric motors and generators in future aircraft. Several prototypes of electrical machines for smaller aircraft already exist, such as the electric drive of the Siemens powered Extra 330LE. The focus of this paper is to provide an overview of current technical possibilities and technical interrelations of high performance electric drives for aviation. A 1 MW drive is exemplified to present the possibilities for future drives for airplanes carrying a larger number of passengers. All presented techniques can also be applied to other drive power classes. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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21 pages, 7575 KiB  
Article
Multifunctional Composites for Future Energy Storage in Aerospace Structures
by Till Julian Adam, Guangyue Liao, Jan Petersen, Sebastian Geier, Benedikt Finke, Peter Wierach, Arno Kwade and Martin Wiedemann
Energies 2018, 11(2), 335; https://0-doi-org.brum.beds.ac.uk/10.3390/en11020335 - 02 Feb 2018
Cited by 86 | Viewed by 9269
Abstract
Multifunctionalization of fiber-reinforced composites, especially by adding energy storage capabilities, is a promising approach to realize lightweight structural energy storages for future transport vehicles. Compared to conventional energy storage systems, energy density can be increased by reducing parasitic masses of non-energy-storing components and [...] Read more.
Multifunctionalization of fiber-reinforced composites, especially by adding energy storage capabilities, is a promising approach to realize lightweight structural energy storages for future transport vehicles. Compared to conventional energy storage systems, energy density can be increased by reducing parasitic masses of non-energy-storing components and by benefitting from the composite meso- and microarchitectures. In this paper, the most relevant existing approaches towards multifunctional energy storages are reviewed and subdivided into five groups by distinguishing their degree of integration and their scale of multifunctionalization. By introducing a modified range equation for battery-powered electric aircrafts, possible range extensions enabled by multifunctionalization are estimated. Furthermore, general and aerospace specific potentials of multifunctional energy storages are discussed. Representing an intermediate degree of structural integration, experimental results for a multifunctional energy-storing glass fiber-reinforced composite based on the ceramic electrolyte Li1.4Al0.4Ti1.6(PO4)3 are presented. Cyclic voltammetry tests are used to characterize the double-layer behavior combined with galvanostatic charge–discharge measurements for capacitance calculation. The capacitance is observed to be unchanged after 1500 charge–discharge cycles revealing a promising potential for future applications. Furthermore, the mechanical properties are assessed by means of four-point bending and tensile tests. Additionally, the influence of mechanical loads on the electrical properties is also investigated, demonstrating the storage stability of the composites. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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12 pages, 1017 KiB  
Article
A Generic Approach to Analyze the Impact of a Future Aircraft Design on the Boarding Process
by Bekir Yildiz, Peter Förster, Thomas Feuerle, Peter Hecker, Stefan Bugow and Stefan Helber
Energies 2018, 11(2), 303; https://0-doi-org.brum.beds.ac.uk/10.3390/en11020303 - 30 Jan 2018
Cited by 7 | Viewed by 7474
Abstract
The turnaround process constitutes an important part of the air transportation system. Airports often represent bottlenecks in air traffic management (ATM), thus operations related to the preparation of the aircraft for the next flight leg have to be executed smoothly and in a [...] Read more.
The turnaround process constitutes an important part of the air transportation system. Airports often represent bottlenecks in air traffic management (ATM), thus operations related to the preparation of the aircraft for the next flight leg have to be executed smoothly and in a timely manner. The ATM significantly depends on a reliable turnaround process. Future paradigm changes with respect to airplane energy sources, aircraft design or propulsion concepts will also influence the airport layout. As a consequence, operational processes associated with the turnaround will be affected. Airlines aim for efficient and timely turnaround operations that are correlated with higher profits. This case study discusses an approach to investigate a new aircraft design with respect to the implications on the turnaround. The boarding process, as part of the turnaround, serves as an example to evaluate the consequences of new design concepts. This study is part of an interdisciplinary research to investigate future energy, propulsion and designs concepts and their implications on the whole ATM system. Due to these new concepts, several processes of the turnaround will be affected. For example, new energy storage concepts will influence the fueling process on the aircraft itself or might lead to a new infrastructure at the airport. This paper aims to evaluate the applied methodology in the case of a new boarding process, due to a new aircraft design, by means of a generic example. An agent-based boarding simulation is applied to assess passenger behavior during boarding, particularly with regard to cabin layout and seat configuration. The results of the generic boarding simulation are integrated into a simplified, deterministic and generic simulation of the turnaround process. This was done to assess the proposed framework for future investigations which on the one hand address the ATM system holistically and on the other, incorporate additional or adapted processes of the turnaround. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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16 pages, 1721 KiB  
Article
Location Planning for Dynamic Wireless Charging Systems for Electric Airport Passenger Buses
by Stefan Helber, Justine Broihan, Young Jae Jang, Peter Hecker and Thomas Feuerle
Energies 2018, 11(2), 258; https://0-doi-org.brum.beds.ac.uk/10.3390/en11020258 - 23 Jan 2018
Cited by 33 | Viewed by 6392
Abstract
The majority of the ground vehicles operating on the airside parts of commercial airports are currently powered by diesel engines. These include vehicles such as apron buses, fuel trucks, and aircraft tractors. Hence, these vehicles contribute to the overall CO 2 emissions of [...] Read more.
The majority of the ground vehicles operating on the airside parts of commercial airports are currently powered by diesel engines. These include vehicles such as apron buses, fuel trucks, and aircraft tractors. Hence, these vehicles contribute to the overall CO 2 emissions of the aviation transport system and thus negatively influence its environmental footprint. To reduce this damaging environmental impact, these vehicles could potentially be electrified with on-board batteries as their energy sources. However, the conductive charging of such vehicles via stationary cable connections is rather time-consuming. A dynamic wireless charging system to supply public transportation passenger buses with electric energy while in motion has recently been installed on the Korea Advanced Institute of Science and Technology (KAIST) campus and in the Korean city of Gumi. In this paper, we study configuration problems related to the use of this technology to make airport operations more environmentally sustainable. We concentrate on the power supply for apron buses and analyze the location planning problems related to the distribution of the required power supply and the wireless charging units in the apron road system. To this end, we develop a formal optimization model and discuss the first numerical results. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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28 pages, 8967 KiB  
Article
Drag Reduction by Laminar Flow Control
by Nils Beck, Tim Landa, Arne Seitz, Loek Boermans, Yaolong Liu and Rolf Radespiel
Energies 2018, 11(1), 252; https://0-doi-org.brum.beds.ac.uk/10.3390/en11010252 - 20 Jan 2018
Cited by 75 | Viewed by 11209
Abstract
The Energy System Transition in Aviation research project of the Aeronautics Research Center Niedersachsen (NFL) searches for potentially game-changing technologies to reduce the carbon footprint of aviation by promoting and enabling new propulsion and drag reduction technologies. The greatest potential for aerodynamic drag [...] Read more.
The Energy System Transition in Aviation research project of the Aeronautics Research Center Niedersachsen (NFL) searches for potentially game-changing technologies to reduce the carbon footprint of aviation by promoting and enabling new propulsion and drag reduction technologies. The greatest potential for aerodynamic drag reduction is seen in laminar flow control by boundary layer suction. While most of the research so far has been on partial laminarization by application of Natural Laminar Flow (NLF) and Hybrid Laminar Flow Control (HLFC) to wings, complete laminarization of wings, tails and fuselages promises much higher gains. The potential drag reduction and suction requirements, including the necessary compressor power, are calculated on component level using a flow solver with viscid/inviscid coupling and a 3D Reynolds-Averaged Navier-Stokes (RANS) solver. The effect on total aircraft drag is estimated for a state-of-the-art mid-range aircraft configuration using preliminary aircraft design methods, showing that total cruise drag can be halved compared to today’s turbulent aircraft. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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26 pages, 4874 KiB  
Article
Conceptual Design of Operation Strategies for Hybrid Electric Aircraft
by Julian Hoelzen, Yaolong Liu, Boris Bensmann, Christopher Winnefeld, Ali Elham, Jens Friedrichs and Richard Hanke-Rauschenbach
Energies 2018, 11(1), 217; https://0-doi-org.brum.beds.ac.uk/10.3390/en11010217 - 16 Jan 2018
Cited by 135 | Viewed by 18434
Abstract
Ambitious targets to reduce emissions caused by aviation in the light of an expected ongoing rise of the air transport demand in the future drive the research of propulsion systems with lower CO2 emissions. Regional hybrid electric aircraft (HEA) powered by conventional [...] Read more.
Ambitious targets to reduce emissions caused by aviation in the light of an expected ongoing rise of the air transport demand in the future drive the research of propulsion systems with lower CO2 emissions. Regional hybrid electric aircraft (HEA) powered by conventional gas turbines and battery powered electric motors are investigated to test hybrid propulsion operation strategies. Especially the role of the battery within environmentally friendly concepts with significantly reduced carbon footprint is analyzed. Thus, a new simulation approach for HEA is introduced. The main findings underline the importance of choosing the right power-to-energy-ratio of a battery according to the flight mission. The gravimetric energy and power density of the electric storages determine the technologically feasibility of hybrid concepts. Cost competitive HEA configurations are found, but do not promise the targeted CO2 emission savings, when the well-to-wheel system is regarded with its actual costs. Sensitivity studies are used to determine external levers that favor the profitability of HEA. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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17 pages, 1848 KiB  
Article
Simulation-Based Analysis of the Potential of Alternative Fuels towards Reducing CO2 Emissions from Aviation
by Karsten Kieckhäfer, Gunnar Quante, Christoph Müller, Thomas Stefan Spengler, Matthias Lossau and Wolfgang Jonas
Energies 2018, 11(1), 186; https://0-doi-org.brum.beds.ac.uk/10.3390/en11010186 - 12 Jan 2018
Cited by 17 | Viewed by 7763
Abstract
The mid-term framework of global aviation is shaped by air travel demand growth rates of 2–5% p.a. and ambitious targets to reduce aviation-related CO2 emissions by up to 50% until 2050. Alternative jet fuels such as bio- or electrofuels can be considered [...] Read more.
The mid-term framework of global aviation is shaped by air travel demand growth rates of 2–5% p.a. and ambitious targets to reduce aviation-related CO2 emissions by up to 50% until 2050. Alternative jet fuels such as bio- or electrofuels can be considered as a potential means towards low-emission aviation. While these fuels offer significant emission reduction potential, their market success depends on manifold influencing factors like the maturity of the production technology or the development of the price of conventional jet fuel. To study the potential for adoption of alternative jet fuels in aviation and the extent to which alternative fuels can contribute to the reduction targets, we deploy a System Dynamics approach. The results indicate that the adoption of alternative fuels and therefore their potential towards low-emissions aviation is rather limited in most scenarios considered since current production processes do not allow for competitive prices compared to conventional jet fuel. This calls for the development of new production processes that allow for economic feasibility of converting biomass or hydrogen into drop-in fuels as well as political measures to promote the adoption of alternative fuels. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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21 pages, 1790 KiB  
Article
Design Considerations for the Electrical Power Supply of Future Civil Aircraft with Active High-Lift Systems
by J.-K. Mueller, A. Bensmann, B. Bensmann, T. Fischer, T. Kadyk, G. Narjes, F. Kauth, B. Ponick, J. R. Seume, U. Krewer, R. Hanke-Rauschenbach and A. Mertens
Energies 2018, 11(1), 179; https://0-doi-org.brum.beds.ac.uk/10.3390/en11010179 - 11 Jan 2018
Cited by 13 | Viewed by 6740
Abstract
Active high-lift systems of future civil aircraft allow noise reduction and the use of shorter runways. Powering high-lift systems electrically have a strong impact on the design requirements for the electrical power supply of the aircraft. The active high-lift system of the reference [...] Read more.
Active high-lift systems of future civil aircraft allow noise reduction and the use of shorter runways. Powering high-lift systems electrically have a strong impact on the design requirements for the electrical power supply of the aircraft. The active high-lift system of the reference aircraft design considered in this paper consists of a flexible leading-edge device together with a combination of boundary-layer suction and Coanda-jet blowing. Electrically driven compressors distributed along the aircraft wings provide the required mass flow of pressurized air. Their additional loads significantly increase the electric power demand during take-off and landing, which is commonly provided by electric generators attached to the aircraft engines. The focus of the present study is a feasibility assessment of alternative electric power supply concepts to unburden or eliminate the generator coupled to the aircraft engine. For this purpose, two different concepts using either fuel cells or batteries are outlined and evaluated in terms of weight, efficiency, and technology availability. The most promising, but least developed alternative to the engine-powered electric generator is the usage of fuel cells. The advantages are high power density and short refueling time, compared to the battery storage concept. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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22 pages, 5339 KiB  
Article
Exploring Vehicle Level Benefits of Revolutionary Technology Progress via Aircraft Design and Optimization
by Yaolong Liu, Ali Elham, Peter Horst and Martin Hepperle
Energies 2018, 11(1), 166; https://0-doi-org.brum.beds.ac.uk/10.3390/en11010166 - 10 Jan 2018
Cited by 36 | Viewed by 6151
Abstract
It is always a strong motivation for aeronautic researchers and engineers to reduce the aircraft emissions or even to achieve emission-free air transport. In this paper, the impacts of different game-changing technologies together on the reduction of aircraft fuel consumption and emissions are [...] Read more.
It is always a strong motivation for aeronautic researchers and engineers to reduce the aircraft emissions or even to achieve emission-free air transport. In this paper, the impacts of different game-changing technologies together on the reduction of aircraft fuel consumption and emissions are studied. In particular, a general tool has been developed for the technology assessment, integration and also for the overall aircraft multidisciplinary design optimization. The validity and robustness of the tool has been verified through comparative and sensitivity studies. The overall aircraft level technology assessment and optimization showed that promising fuel efficiency improvements are possible. Though, additional strategies are required to reach the aviation emission reduction goals for short and medium range configurations. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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20 pages, 1296 KiB  
Article
Exploring the Effect of Increased Energy Density on the Environmental Impacts of Traction Batteries: A Comparison of Energy Optimized Lithium-Ion and Lithium-Sulfur Batteries for Mobility Applications
by Felipe Cerdas, Paul Titscher, Nicolas Bognar, Richard Schmuch, Martin Winter, Arno Kwade and Christoph Herrmann
Energies 2018, 11(1), 150; https://0-doi-org.brum.beds.ac.uk/10.3390/en11010150 - 08 Jan 2018
Cited by 53 | Viewed by 9345
Abstract
The quest towards increasing the energy density of traction battery technologies has led to the emergence and diversification of battery materials. The lithium sulfur battery (LSB) is in this regard a promising material for batteries due to its specific energy. However, due to [...] Read more.
The quest towards increasing the energy density of traction battery technologies has led to the emergence and diversification of battery materials. The lithium sulfur battery (LSB) is in this regard a promising material for batteries due to its specific energy. However, due to its low volumetric energy density, the LSB faces challenges in mobility applications such as electric vehicles but also other transportation modes. To understand the potential environmental implication of LSB batteries, a comparative Life Cycle Assessment (LCA) was performed. For this study, electrodes for both an NMC111 with an anode graphite and a LSB battery cell with a lithium metal foil as anode were manufactured. Data from disassembly experiments performed on a real battery system for a mid-size passenger vehicle were used to build the required life cycle inventory. The energy consumption during the use phase was calculated using a simulative approach. A set of thirteen impact categories was evaluated and characterized with the ReCiPe methodology. The results of the LCA in this study allow identification of the main sources of environmental problems as well as possible strategies to improve the environmental impact of LSB batteries. In this regard, the high requirements of N-Methyl-2-pyrrolidone (NMP) for the processing of the sulfur cathode and the thickness of the lithium foil were identified as the most important drivers. We make recommendations for necessary further research in order to broaden the understanding concerning the potential environmental implication of the implementation of LSB batteries for mobility applications. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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23 pages, 883 KiB  
Article
Modelling and Designing Cryogenic Hydrogen Tanks for Future Aircraft Applications
by Christopher Winnefeld, Thomas Kadyk, Boris Bensmann, Ulrike Krewer and Richard Hanke-Rauschenbach
Energies 2018, 11(1), 105; https://0-doi-org.brum.beds.ac.uk/10.3390/en11010105 - 03 Jan 2018
Cited by 78 | Viewed by 12636
Abstract
In the near future, the challenges to reduce the economic and social dependency on fossil fuels must be faced increasingly. A sustainable and efficient energy supply based on renewable energies enables large-scale applications of electro-fuels for, e.g., the transport sector. The high gravimetric [...] Read more.
In the near future, the challenges to reduce the economic and social dependency on fossil fuels must be faced increasingly. A sustainable and efficient energy supply based on renewable energies enables large-scale applications of electro-fuels for, e.g., the transport sector. The high gravimetric energy density makes liquefied hydrogen a reasonable candidate for energy storage in a light-weight application, such as aviation. Current aircraft structures are designed to accommodate jet fuel and gas turbines allowing a limited retrofitting only. New designs, such as the blended-wing-body, enable a more flexible integration of new storage technologies and energy converters, e.g., cryogenic hydrogen tanks and fuel cells. Against this background, a tank-design model is formulated, which considers geometrical, mechanical and thermal aspects, as well as specific mission profiles while considering a power supply by a fuel cell. This design approach enables the determination of required tank mass and storage density, respectively. A new evaluation value is defined including the vented hydrogen mass throughout the flight enabling more transparent insights on mass shares. Subsequently, a systematic approach in tank partitioning leads to associated compromises regarding the tank weight. The analysis shows that cryogenic hydrogen tanks are highly competitive with kerosene tanks in terms of overall mass, which is further improved by the use of a fuel cell. Full article
(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)
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