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P&W on A320neo: More pressure, less cooling

Pratt & Whitney plans to boost the overall pressure ratio of its PW1100G geared turbofan engine for the A320neo to about 50:1, up 11% from the 45:1 ratio at takeoff power for the Bombardier CSeries' PW1524G.

The manufacturer will also cut further the amount of parasitic cooling air for the turbines compared with the baseline CSeries engine.

Combined with a 206cm (81in) fan size, the pressure hike and reduced cooling air are key ingredients that will yield a 15% decrease in fuel burn for the PW1100G compared with a current CFM International CFM56-5B-powered A320, says P&W.

P&W is in the preliminary design phase for the turbofan, variants of which will also power the Mitsubishi MRJ regional jet and Irkut MS-21. P&W next-generation product family vice-president Bob Saia says the A320neo programme will be fully staffed early next year, with first engine to test by the end of 2012.

Airbus has received 332 commitments and orders for the A320neo and A321neo to date, with the PW1100G winning 240 airframes. CFM's rival Leap-X has yet to be selected.

Unlike the previous engines, the PW1100G is not a direct scale-up of the core. "It's scaled with technology insertion," says P&W senior vice-president of engineering Paul Adams.

The additional pressure increase over the PW1524G will come from the low pressure compressor, which will act like a supercharger for the A320neo, says Adams.

To keep temperatures in check at the two-stage high-pressure turbine, P&W is developing new single-crystal nickel aerofoil blades, disk alloys and thermal barrier coatings as well as casting techniques for better cooling, some of which were developed for the CSeries and refined for the A320neo.

Adams says another advantage of the gearing system, beyond a boost to propulsive efficiency, is that it allows the P&W engine to run "substantially cooler" than its competitors at the combustor exit.

The lower exit temperature, combined with the better cooling techniques and technologies for the turbine section, means the PW1100G will require 5% less turbine cooling air from the compressor compared with the PW1524G, which itself requires 20% less cooling air "than we have historically used", says Adams.

P&W is working with Portland, Oregon-based Precision Castparts to develop the casting technologies and subsidiary HMI Metal Powders for the new turbine alloy disks.

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