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FARNBOROUGH: New turbofan concept promises large NOx reductions

UK engineering firm Derwent Aviation Consulting has developed a new engine architecture that promises to halve nitrogen oxide (NOx) emissions and generate part of its thrust through electrical power.

The company, led by Charles Cuddington – Rolls-Royce's former chief commercial officer for large engines – has devised a concept under which a turbofan's low-pressure compressor, or booster, is driven by both the low- and high-pressure turbines, rather than just the LPT in a conventional two-spool layout.

This is to be facilitated by a planetary gearbox linking the engine's low-pressure and high-pressure shafts.

Cuddington says that layout would increase booster speed and efficiency, and would reduce turbine temperature during take-off.

In addition, the engineers foresee embedding of an electrical generator/motor within the booster being directly driven by the gearbox.

In a conventional turbofan, electrical generators are located on the outside of an engine and are driven by a linkage with the powerplant's shafts.

On a medium-thrust engine like the CFM International Leap, the new booster-generator configuration could extract 2MW of electrical power, Cuddington says.

Combined with batteries on board the aircraft, the electrical generator/motor layout could be used to provide power assistance for take-off and climb, he says.

Cuddington notes that the battery configuration would not be suitable for long-haul flight as the equipment's weight would negate any fuel efficiencies.

But for distances of 800-1,000nm (1,500-1,900km), the engineers project NOx emission reductions of up to 50% and fuel-burn savings of between 3% and 4% for single-aisle aircraft like the Airbus A320-family and Boeing 737.

Cuddington says the "dual-drive booster" concept can be "tuned" to shift the balance between NOx emissions and fuel efficiency, and that he is confident the layout would generate fuel-burn savings similar to the latest generation of engines like the Leap.

He concedes that the new layout would be incompatible with a geared-fan architecture, like on Pratt & Whitney's PW1000G and Rolls-Royce's UltraFan future engine programme. But he says the dual-drive booster would deliver notable NOx emission reductions versus latest-generation powerplants.

Patents have been secured in the UK, China and USA, and talks are under way with several engine manufacturers, including R-R, about potential application options.

Derwent has collaborated with the University of Nottingham to prove the concept's mechanical feasibility, and with Aachen University in Germany to project the engine's performance.

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