Comparison of the Potential Environmental Impact Improvements of Future Aircraft Concepts Using Life Cycle Assessment
Background. The protection of the environment gets increased importance in civil aviation . However, today aircraft are designed mainly for lowest Direct Operating Costs (DOC). Clearly, a better environmental protection can be achieved, if Environmental Impact (EI) is minimized and used as the objective function in aircraft design optimization. EIs over the entire life cycle can be calculated with a Life Cycle Assessment (LCA) defined in ISO 14040. LCA is the „compilation and evaluation of the inputs, outputs and the potential EIs of a product system during its life cycle” . Admittedly, in a practical design of future civil aircraft, DOC will remain the most important objective, but better environmental protection could be achieved already with a multi objective design optimization in which EI are included and are given a least a certain weight. As often explained, most characteristics of an aircraft are fixed and determined already in the early phases of aircraft design. The same is true for the Environmental Impact (EI) of an aircraft which is also locked in by decisions made in conceptual aircraft design. Therefore, it is so important to include a full LCA already in conceptual design and not merely an analysis of the pollutant emissions resulting from aircraft operation. Summing up: Environmental protection is made a more important design criterion by including a comprehensive LCA (calculating EI) into the objective function for aircraft optimization already during conceptual aircraft design. Extending the application of LCA in conceptual aircraft design. The authors showed already that with a simplified but still comprehensive LCA methodology the EI of an aircraft can be calculated already during conceptual aircraft design . The authors showed further that using the EI as the objective function in conceptual aircraft design instead of using DOC has an influence on resulting aircraft parameters . Not only aircraft parameters are influenced in new ways using EI as the objective function. This paper shows that EI can also be used to select the best alternative among several future aircraft concepts. Future aircraft described and reviewed. The paper describes several promising future aircraft with different fuel concepts and reviews their pros and cons. The considered aircraft and fuel concepts are: a) biofuelpowered or synthetic fuel-powered aircraft, b) hydrogenpowered aircraft, c) hybrid-electric-powered or allelectric-powered aircraft. Existing studies on these future concepts are analysed to get a first qualitative understanding of the concepts’ impact on the EI of an aircraft. Also new technologies like a higher share of carbon fiber reinforced plastics are investigated concerning their influence on the EI of aircraft. Future aircraft designed, optimized, and analysed. Aircraft are designed e.g. for hydrogen fuel, determining the best position of the liquid hydrogen tanks. For a selected design solution the aircraft parameters are optimized for minimum EI. The EI and the main contributors to the EI are analysed among the considered aircraft and their fuel concepts. The results of the investigated concepts are compared to those of the reference aircraft Airbus A320200 and also to a possible conventional successor of the A320, a turboprop aircraft optimized for minimum EI (presented in Figures 1 ... 3 in the attached file). The paper presents by how much future technologies could possibly reduce the EI of an aircraft and what concepts are favourable concerning their EI. Selected results. A continued increase of the share of carbon fiber decreases the EI of aircraft due to savings in weight and therefore fuel even though the EI in the disposal phase is impaired. Considering the current European electricity mix, biofuels made of microalgae surprisingly lead to a doubling of the EI of aircraft. This is because of the high energy demand during the production of the biofuels. Biofuel-powered aircraft can therefore only substantially reduce the EI if the energy demand from the production is covered by renewable energy sources also having low EI. Hydrogenpowered aircraft also have the issue of high energy demand due to the production of hydrogen as well as water vapor emissions during cruise causing contrails and contrail-induced cirrus clouds both having substantial negative EI. In total, the EI would even be increased by few percent compared to the reference aircraft. But, by adapting the flight altitude to counteract the effect of contrail formation, EI could be reduced by about 70 %. If renewable energy sources are additionally used for the production of hydrogen, EI could be lowered by another 25 %. Hybridelectric and all-electric aircraft also only allow to drastically reduce the EI if their energy needs are covered by renewable energy sources. With the current European electricity mix, EI could only be reduced by less than 20 %. Summarized, as long as the share of renewable energy sources stays low (which will presumably be the case for the next decades), only a lowflying hydrogenpowered aircraft offers high improvements concerning the EI.