Pratt & Whitney has apparently perfected a geared turbofan engine for airliners. The gearing is 3:1 between the stuff in the back (compressor and hot section) and the big fan in front.
The upshot is P&W is promising a 16% reduction in fuel burn, 50% reduction in carbon emissions and a whopping 75% reduction in noise. they seem to think that they can improve on that and get fuel usage down by 20% over current engines.
For the airline industry, this is huge. It's beyond huge.
It may be hype, too, but even a 10% reduction in fuel burn will be the sort of thing that airline executives would sell their mothers for.
I'd expect that if this is as good as they are promising, P&W will end up licensing their technology to the other engine companies. albeit maybe under considerable pressure to do so.
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Wednesday, July 19, 2017
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Where is the line between turbofan and turboprop?
ReplyDeleteB, the big difference is that a turbo-prop engine has a reduction gearbox that reduces the output rpm quite drastically. A small PT6 engine (I'm talking about the -21,-27,-34, etc) has a power turbine rpm of 37,500rpm and a prop rpm of 2,200. Most turbofans have no gearbox at all, the low pressure turbine wheels are attached to the inner most of two or three shafts and the fan is bolted to the front end. On the A-10 Warthog the fan is turning at over 7,000rpm. The civilian CF34-1A has a 7,700rpm fan speed IIRC.
ReplyDeleteThe problem that P&W is trying to solve is that turbine wheels are more efficient at very high rpm >10,000 but the fan is more efficient at lower rpm <5,000. By gearing the fan down both the turbine and fan can turn at their most efficient speeds, burning less fuel. The problem is that there is tremendous stress, the gearbox must handle 30,000hp and be as small, light and reliable as possible.
Al_in_Ottawa
Not to mention that it's much quieter to run the fan at a lower rpm because the blades are no longer exceeding the speed of sound, which causes the loud howling noise of most turbofans. The BAe 146 was boasted to be the quietest feeder jet on the planet when it was introduced with four 6500 lbf thrust Avco Lycoming ALF 502H turbofan engines in 1980. Those are a geared turbofan engine that basically took a Chinook helicopter turboshaft engine and geared it to drive a fan rather than a helicopter rotor.
ReplyDeleteUhm, yeah, needless to say P&W is not the first to have a geared turbofan. They've been used on smaller jets for quite some years, such as on the Learjet 31, which uses TFE731 geared turbofans. They *are*, however, the first to make it for big turbofans. Prior to this the ALF with its 6500 lbf thrust was the biggest geared turbofan on the planet. Being able to produce 35,000 lbf thrust with a geared turbofan is a game changer, because it lets them engine the big boys, not just commuter jets and puddle jumpers.
External propeller is the line.
ReplyDeleteLRod
ZJX, ORD, ZAU retired
There was an experimental rear-mounted turbofan with unshrouded blades. It was developed during the oil shocks in the '70s. It went nowhere when oil prices collapsed in the '80s.
ReplyDeleteMD-80 UDF was the demo for that project, Comrade.
ReplyDelete