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As aviation is one of the fastest growing industrial sectors world wide, air-traffic emissions are projected to increase their stake in the contribution to global warming. According to studies, both carbon dioxide and contrails are the principal air-traffic pollutants, whereas the impact from contrails in terms of radiative forcing is possibly larger than that of all other air-traffic pollutants combined. New regulations with the objective of mitigating contrail occurrences might cause a change in the design requirements of aircraft. In light of this, a method considering contrail formation during the aircraft design process is presented in this paper. Aircraft performance and optimisation is carried out with NASA’s flight optimisation system. Combining historical meteorological data with air-traffic data enables an assessment regarding contrail formation. As an example, a particular aircraft type in terms of range, speed and payload is optimised for minimum block fuel consumption considering different altitudes. The change in contrail formation in terms of contrail-km formed is calculated. The results suggest that if aircraft of the considered class were designed for higher altitudes, contrail occurrences would diminish slightly at a non-negligible fuel burn penalty.

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The climatic effects of air-traffic pollutants, such as carbon dioxide (CO2) and mononitrogen oxides (NOx), aerosols, contrails, and aviation induced cirrus clouds, are repeatedly stressed in assessment reports. It is therefore desired to reduce all aviation emissions simultaneously. In this paper, a novel propulsion concept, which has the potential to reduce all pollutants, is assessed regarding its performance. It is based on gas turbine technology, derived from the intercooled and recuperated engine cycle. Exhaust water condensation is facilitated inside the engine to avoid the formation of contrails. Particles and aerosols are scavenged from the exhaust gases during condensation. The condensed water is partially redirected into the combustion chamber to mitigate NOx emissions via water injection technique. Calculations suggest that this new concept allows higher thermal efficiencies than conventional designs, yielding in better fuel economy and hence reduces greenhouse gas emissions. The corresponding design parameters for bypass ratio and fan pressure ratio suggest that this concept might be well suited for propfans or remotely driven fans.

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