On the Design of Energy Efficient Aero Engines: Some Recent Innovations

Sammanfattning: In the light of the energy crisis of the 1970s, the old aerospace paradigm of flying higher and faster shifted towards the development of more energy efficient air transport solutions. Today, the aeronautical research and development community is more prone to search for innovative solutions, in particular since the improvement rate of change is decelerating somewhat in terms of energy efficiency, which still is far from any physical limits of aero engine and aircraft design. The Advisory Council for Aeronautics Research in Europe has defined a vision for the year of 2020 for aeronautical research in Europe which states a 50% reduction in CO2, 80% reduction in NOx and a 50% reduction in noise. Within this thesis work, methods for conceptual design of aero engines and aircraft performance have been developed and applied to evaluate some innovative aero engine concepts that have the potential to fulfil or even surpass society’s expectations on the aerospace industry in the future. In particular, the impact of a varying engine size and weight on the aircraft performance has been modelled in order to quantify the fuel consumption of different aero engine concepts. Furthermore, methods for designing and analyzing propeller performance have been developed. The methods have been incorporated into a multidisciplinary optimization environment which gives the benefit of interdisciplinary quantification of design changes and the impact of those on energy efficiency. The potential of the variable cycle engine for medium range jets were studied and the results showed a quite large reduction in fuel consumption compared to the conventional turbofan engine. Furthermore, the inter-turbine reheated aero engine concept was evaluated and the results indicated a large NOx reduction potential at almost the same energy efficiency as the conventional engine. The idea of applying catalytic combustion in aero engines was also studied showing potential of significant reductions of NOx. Finally, an innovative propeller design based on Prandtl’s work in the 1920s is suggested and discussed. This work has contributed with new methods for conceptual aero engine design that are in use within the industry and academia. The results from the studies concerning innovative aero engine concepts show that major improvements in terms of energy efficiency and emissions still are possible for the aerospace industry to achieve.