This thesis assesses the feasibility of turbo-, hybrid-, and fully-electric aircraft propulsion systems to enable more efficient air transport. A modular optimization framework was developed to quantify system performance for single-aisle transport aircraft with a mission similar to a Boeing 737 MAX 8. Various propulsion systems leveraging superconducting motors, boundary layer ingestion, high-temperature PEM fuel cells, and liquid hydrogen fuel were examined. Aviation turbine fuel (ATF) and liquid hydrogen were compared using the payload-fuel energy intensity (PFEI), defined as the fuel energy required per product of range and payload. For a given mission, it was found that a hydrogen-fueled fully-electric configuration required similar fuel energy compared to an ATF-burning turbo-fan propulsion system (PFEI = 5.0). Relative to these systems, a hydrogen-fueled turbo-fan had 14% lower PFEI, an ATF-burning turbo-electric propulsion system had 23% higher PFEI, a hydrogen-fueled turbo-electric propulsion system had 8% lower PFEI, and a hydrogen-fueled hybrid-electric had 3% lower PFEI for the same mission.
This thesis assesses the performance benefit of electrified propulsion systems for commercial aircraft entering production in a 2035 timeframe. The propulsive power reduction from boundary layer ingestion (BLI), a technology that could be enhanced by electrification, is characterized and bounded by power balance analysis. An aircraft system model extends this analysis to capture the weight and performance trades of electrified architectures, as defined by propulsion system configuration, technology level, and mission. The model quantifies the impact of such architectures on mission energy via optimized aircraft designs. It is found that the propulsive power of a representative narrow-body jet is reduced by 28% with ideal ingestion of the entire boundary layer. Distributed, boundary layer ingesting, turbo-electric aircraft configurations are found to minimize energy consumption for all the missions examined from 500 to 6000 nmi. Energy reductions up to 27% relative to a non-BLI, non-electric, twin-turbofan design are possible. Advanced non-electric aircraft configurations are also examined and found to achieve similar reductions (up to 24%) with fuselage BLI. A parametric characterization of the trade space of electrified configurations illustrates the benefit of a turbo-electric architecture for all the technology levels and missions examined and the limitation of all-electric architecture to mission ranges less than 300 nmi, even with optimistic technology levels.
The primary human activities that release carbon dioxide (CO2) into the atmosphere are the combustion of fossil fuels (coal, natural gas, and oil) to generate electricity, the provision of energy for transportation, and as a consequence of some industrial processes. Although aviation CO2 emissions only make up approximately 2.0 to 2.5 percent of total global annual CO2 emissions, research to reduce CO2 emissions is urgent because (1) such reductions may be legislated even as commercial air travel grows, (2) because it takes new technology a long time to propagate into and through the aviation fleet, and (3) because of the ongoing impact of global CO2 emissions. Commercial Aircraft Propulsion and Energy Systems Research develops a national research agenda for reducing CO2 emissions from commercial aviation. This report focuses on propulsion and energy technologies for reducing carbon emissions from large, commercial aircraftâ€" single-aisle and twin-aisle aircraft that carry 100 or more passengersâ€"because such aircraft account for more than 90 percent of global emissions from commercial aircraft. Moreover, while smaller aircraft also emit CO2, they make only a minor contribution to global emissions, and many technologies that reduce CO2 emissions for large aircraft also apply to smaller aircraft. As commercial aviation continues to grow in terms of revenue-passenger miles and cargo ton miles, CO2 emissions are expected to increase. To reduce the contribution of aviation to climate change, it is essential to improve the effectiveness of ongoing efforts to reduce emissions and initiate research into new approaches.
The Electric-powered general aviation aircraft, DA-II, represents a major step forward in environmentally friendly vehicle technology. DA-II has been designed to provide clean, quiet, and convenient service for civilian air travel. Electric propulsion was chosen for several reasons. First, by not using an internal combustion engine, the aircraft can greatly reduce air pollution. The electric propulsion is also quiet compared to conventional internal combustion engines. The final reason for choosing electric propulsion is to explore the feasibility of this technology in a commercially viable single propeller aircraft. The basic design philosophy behind the DA-II is to build an easily maintainable, efficient aircraft that could be used in general aviation. Due to its high specific energy density, i.e., the amount of energy stored in a given system or region of space per unit volume or mass depending on the context, a proton exchange membrane (PEM) hydrogen fuel cell system is used as the primary power plant for the DA-II. In order to better understand the design and performance tradeoffs for a hydrogen fuel cell and its feasibility on electric powered aircraft, a conceptual design study of a small-scale aircraft is performed. A propulsion system consisting of a liquid cooled PEM fuel cell with cryogenic liquid hydrogen storage powering a single electric pusher propeller motor is chosen. The aerodynamic configuration consists of a high-aspect ratio un-tapered wing and fuselage with single T-tail. Several aircraft design trade studies are done and the most efficient parameters for the DA-II aircraft are chosen. The results showed that the electric powered aircraft is feasible. However, the analysis also showed that a design of an electric powered aircraft using fuel cell energy did not produce the best aircraft design for either long range or long endurance. Technology is still immature for these high expectations. Additional improvements in energy storage density are needed to achieve the performance needed for strong market acceptance.
Aviation propulsion development continues to rely upon fossil fuels for the vast majority of commercial and military applications. Until these fuels are depleted or abandoned, burning them will continue to jeopardize air quality and provoke increased regulation. With those challenges in mind, research and development of more efficient and electric propulsion systems will expand. Fuel-cell technology is but one example that addresses such emission and resource challenges, and others, including negligible acoustic emissions and the potential to leverage current infrastructure models. For now, these technologies are consigned to smaller aircraft applications, but are expected to mature toward use in larger aircraft. Additionally, measures such as electric/conventional hybrid configurations will ultimately increase efficiencies and knowledge of electric systems while minimizing industrial costs. Requirements for greater flight time, stealth characteristics, and thrust-to-power ratios adds urgency to the development of efficient propulsion methods for applications such as UAVs, which looks to technologies such as asymmetrical capacitors to enhance electric propulsion efficiency. This book will take the reader through various technologies that will enable a more-electric aircraft future, as well as design methods and certification requirements of more-electric engines.
Liquid hydrogen is shown to be the ideal fuel for civil transport aircraft, as well as for many types of military aircraft. Hydrogen Aircraft Technology discusses the potential of hydrogen for subsonic, supersonic, and hypersonic applications. Designs with sample configurations of aircraft for all three speed categories are presented, in addition to performance comparisons to equivalent designs for aircraft using conventional kerosine-type fuel and configurations for aircraft using liquid methane fuel. Other topics discussed include conceptual designs of the principal elements of fuel containment systems required for cryogenic fuels, operational elements (e.g., pumps, valves, pressure regulators, heat exchangers, lines and fittings), modifications for turbine engines to maximize the benefit of hydrogen, safety aspects compared to kerosine and methane fueled designs, equipment and facility designs for servicing hydrogen-fueled aircraft, production methods for liquid hydrogen, and the environmental advantages for using liquid hydrogen. The book also presents a plan for conducting the necessary development of technology and introducing hydrogen fuel into the worldwide civil air transport industry. Hydrogen Aircraft Technology will provide fascinating reading for anyone interested in aircraft and hydrogen fuel designs.
In 1957, when Russia launched the first satellite, the ability of the United States to respond depended on one small launch vehicle still under development, Vanguard, and modifications to ballistic missiles. The subsequent space race featured a rapid buildup of launch vehicle capability in this country during the 1960s, culminating with the giant Saturn V which launched the Apollo lunar expeditions beginning in 1968. A significant part of the increased launch capability resulted from technical decisions made in 1958 and 1959 to use liquid hydrogen in the upper stages of the Centaur and Saturn vehicles-and that story is not well known. The decision to use liquid hydrogen in developing the nation's largest launch vehicle was particularly bold, for many experienced engineers doubted the advisability of using a highly hazardous fuel associated with the Hindenburg disaster of 1937, a gas difficult to liquefy, a liquid so cold-close to absolute zero-that storage and handling are difficult, and so light-1/14 the density of water-that large tank volumes are required, with attendant problems of vehicle mass and drag. Hydrogen had been considered in astronautics and aeronautics several times before; but in each case, as the problems became better known, the attempt was abandoned, What was different in this case? Why was there so much confidence about hydrogen within the young space agency to warrant risking the success of the nation's manned spaceflight program? The decision, of course, turned out to be the right one. Subsequent advancements in the technologies of liquefying, storing, transporting, and using large quantities of liquid hydrogen made it just another flammable liquid that could be handled and used safely with reasonable caution. The key role that liquid hydrogen played in the success of the Centaur and Saturn launch vehicles has long interested the author. As a participant in research on hydrogen for rockets in the 1950s and a proponent for its use, the author understood the potential as well as the risks and in recent years wanted to investigate more fully the circumstances leading to the 1958 and 1959 decisions. In digging into the background for the decisions and the status of hydrogen technology that influenced those decisions, the question arose: how far back to investigate? The flammability of gaseous hydrogen has been known for centuries; its large heat content was measured in the 18th century; and it was liquefied by Dewar in 1898. Five years later, Tsiolkovskiy, the Russian rocket pioneer, proposed its use in a space rocket, as did Goddard in 1910. In the 1920s, Oberth correctly assessed the advantage of using hydrogen in the upper stages of space vehicles. None of these rocket pioneers experimented with hydrogen; other fuels appeared more attractive in the face of hydrogen's disadvantages, particularly its low density. One German experimenter, Walter Theil, tried to use liquid hydrogen in a small rocket engine a few years before World War II, but numerous leaks and higher priority tasks ended the experiments. The first systematic investigations of liquid hydrogen to propel aircraft and rockets began in the United States in 1945 and although earlier developments undoubtedly had an influence, where the author chose to start this book at that point. In describing the history of rocket technology, it is easy for an engineer-author to become immersed in the technical aspects that may be of little interest to some readers. The author tried to minimize mathematics, technical language, and other specialized details, but some are unavoidable if propulsion research is to be presented fairly and accurately. Adding to this problem has been the conversion of many familiar English units into the metric system. Those accustomed to thinking of rocket performance in terms of specific impulse will not find it here; instead, they will have to settle for its equivalent, exhaust velocity.
A comprehensive review of the science and engineering behind future propulsion systems and energy sources in sustainable aviation Future Propulsion Systems and Energy Sources in Sustainable Aviation is a comprehensive reference that offers a review of the science and engineering principles that underpin the concepts of propulsion systems and energy sources in sustainable air transportation. The author, a noted expert in the field, examines the impact of air transportation on the environment and reviews alternative jet fuels, hybrid-electric and nuclear propulsion and power. He also explores modern propulsion for transonic and supersonic-hypersonic aircraft and the impact of propulsion on aircraft design. Climate change is the main driver for the new technology development in sustainable air transportation. The book contains critical review of gas turbine propulsion and aircraft aerodynamics; followed by an insightful presentation of the aviation impact on environment. Future fuels and energy sources are introduced in a separate chapter. Promising technologies in propulsion and energy sources are identified leading to pathways to sustainable aviation. To facilitate the utility of the subject, the book is accompanied by a website that contains illustrations, and equation files. This important book: Contains a comprehensive reference to the science and engineering behind propulsion and power in sustainable air transportation Examines the impact of air transportation on the environment Covers alternative jet fuels and hybrid-electric propulsion and power Discusses modern propulsion for transonic, supersonic and hypersonic aircraft Examines the impact of propulsion system integration on aircraft design Written for engineers, graduate and senior undergraduate students in mechanical and aerospace engineering, Future Propulsion Systems and Energy Sources in Sustainable Aviation explores the future of aviation with a guide to sustainable air transportation that includes alternative jet fuels, hybrid-electric propulsion, all-electric and nuclear propulsion.
