Sustainable and Green Engine (SAGE) ITD


The Sustainable and Green Engine (SAGE) ITD of Clean Sky demonstrates five engine technologies contributing towards the ACARE (Advisory Council for Aeronautic Research in Europe) environmental targets. There are six engine projects contained in the programme, each targeting specific technologies and market sectors, led by a leading member of the European engines industry.

Open rotor technologies offer the potential for significant reductions in fuel burn and CO2 emissions relative to turbofan engines of equivalent thrust. 

Higher propulsive efficiencies are achieved for turbofans by increasing the bypass ratio through increases in fan diameter but there is a diminishing return to this improvement as nacelle diameters and consequently weight and drag increase. Open rotor engines remove this limitation by operating the propeller blades without a surrounding nacelle, thus enabling ultrahigh bypass ratios to be achieved.

SAGE Open rotor

Further improvements in propulsive efficiency can be gained for open rotor engines by using a second row of propeller blades rotating in opposition to the front row to remove the spin from the column of air to give a more direct thrust.  The technical challenges of counter rotating open rotor engines are many, but are principally:

  • Reduction of the noise created by the propeller blades to counter the loss of attenuation provided by a turbofan nacelle.
  • Definition of the propeller system to reduce the noise created by the counter rotating blades (counter rotating slotted discs in close proximity is the basis siren design and blade interaction noise was the principal issue noted when the open rotor engines were demonstrated in the 1980s)
  • Complexity of communications and blade pitch control through the counter rotating power transmissions system.
  • Installation of the open rotor engine on the airframe.  Turbofans are isolated from the airframe by the nacelle but the airflow through open rotor propellers interacts with the supporting airframe structure and so the installation impacts on the engine system noise and efficiency.
  • Rolls-Royce has developed open rotor propeller design to minimise the noise and demonstrated the effectiveness of these designs through scaled rig testing in the FP7 DREAM programme.  The SAGE1 project is planned to aquire technology for the propulsor system, increasing the Technology Readiness Level (TRL) to TRL 5.

Collaborating in the SAGE1 project under Rolls-Royce leadership are Volvo Aero Corporation and ITP.  Further Partners will be selected through the Clean Sky Call for Proposal process as the project progresses.  Details of these opportunities and the application process will be published on the Clean Sky website: www.cleansky.euLink opens in a new window.

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