Open rotor engines...

Hacia unos motores más eficientes

NASA to fund Boeing for open rotor noise study
http://www.flightglobal.com/articles/2009/11/04/334401/nasa-to-fund-boeing-for-open-rotor-noise-study.html

Boeing and Airbus are both considering new generation and highly efficient open rotor engine designs as potential candidates for the successor to the Boeing 737 and Airbus A320 families of aircraft in the 2020 and timeframe and beyond. Experiments in the 1980s with open rotor designs by several engine manufacturers revealed noise as a key issue in bringing the designs to market.



Powerplant Performance
http://www.aviationweek.com/aw/generic/story_generic.jsp?channel=om&id=news/omengcvr1109.xml&headline=Powerplant%20Performance

Improvements in engine performance are expected to be far more than incremental. For example, the "2008 Addendum To The Strategic Research Agenda, Advisory Council for Aeronautics Research In Europe" (ACARE) sets a goal for European airlines to reduce carbon dioxide emissions by 50%, nitrogen oxide by 80% and perceived external noise by 50% by 2020. At the same time, the industry must make what the council calls "substantial progress towards green manufacturing, maintenance and disposal" by 2020.