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Hybrid geared-fan and piston concept could slash fuel-burn

German aerospace researchers are showing off a high-efficiency powerplant concept which combines geared-fan architecture with a piston-engine core.

While unlikely to enter service before 2050, the concept – described as a composite cycle engine – is potentially capable of halving fuel-burn compared with turbofans from 2000.

The low-pressure section takes advantage of geared-fan technology which ensures that the rotating sections spin at individual optimal speeds.

It has a 16-blade fan with a diameter of 2.87m compared with 2.06m for the Pratt & Whitney PW1100G on the Airbus A320neo.

But the high-pressure shaft is driven by a piston-engine assembly, with two banks and a total of 20 pistons arranged in a V-formation around the centreline of the powerplant.

The piston engine, through the high-pressure spool, powers the axial high-pressure compressor – there is no high-pressure turbine.

Munich-based research institute Bauhaus Luftfahrt, which is presenting the concept at the ILA Berlin air show, says the 5.88m engine length amounts to "only slight enlargement" – some 0.54m – compared with the current geared turbofan.

"The piston engines increase thermal efficiency by using non-stationary isochoric-isobaric combustion," it says.

"[This] enables higher peak pressures and temperatures within the core engine."

The engine would provide thrust of 11,200lb (49.7kN), typical of power levels for current regional jets in the 50-seat sector.

Bauhaus Luftfahrt says the design enables the engine to capitalise on "outstanding" power-to-weight ratio of low-pressure turbines while achieving an "ultra-high" bypass ratio of 33.7.

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