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■ Conventional thermal (gas turbine) engines will continue to be the only way of powering large, long- range aircraft for the next several decades. However, that doesn’t mean that these long-range jets will continue to emit large quantities of CO2.
■ It’s possible to drastically improve the energy efficiency of conventional turbofan engines, in particular by increasing their size and bypass ratio to augment the secondary airflow from the fan, which generates thrust without directly involving combustion.
■ However, the structure and aerodynamic design of tomorrow’s aircraft will still have to be extensively modified. Airframers are actively working on design studies and disruptive aircraft concepts to integrate innovative propulsion systems proposed by engine- makers. Safran’s role is to support aircraft manufacturers in this quest.
■ Above all, these conventional, but ultra-optimized thermal engines could use low-carbon or even carbon- neutral fuels (see pages 24-25). Their basic operating principle would be similar, whether they burn jet fuel, or other types of fuel, including liquid hydrogen.
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Can we significantly reduce the consumption
of conventional jet engines? With the Open Rotor, Safran proved that it was possible. Safran developed this concept through the European research program Clean Sky and carried out ground tests of the first full-scale demonstrator in 2017. It showed fuel savings of up to 15%, thanks to its innovative architecture without a nacelle, plus the use of twin counter-rotating fans and the use of advanced technologies. Despite its unshrouded design, the Open Rotor doesn’t produce any more noise than the current LEAP engine. The results generated by this demonstrator will be used by Safran to develop the enabling technologies for its future engines.
Concept rendering - not representative of any future aircraft configuration.

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