Hopefully this thread can bring together a number of disparate approaches and collect information on the next generation powerplants for the next
generation narrowbodies (and subsequent designs).
It also may direct the readers towards the real battleground between the big two (thats Airbus and Boeing); by comparison the B787 and A350 are mere
As most already know, the current narrowbody market consists of the Boeing 737 and the Airbus A320. Both powered by similar turbofan engines, the 737
having a bypass ratio in the low 5s, the A320 having a bypass ratio in the high 5s... with the core overall pressure ratio (OPR) nearly 33.
Now, looking forward, the only competition for these two is that is currently on the drawing board is Bombardier's CSeries.
Recently, both Boeing and Airbus have indicated they wish to hold off on the narrowbody replacements until the 2022-ish timeframe... due to both
engineering resource availability and engine improvements.
Some of you in the know will be aware of the NASA 2025 or ACARE 2020 goals, namely:
- CO2 reduction by 50%
- NOx reduction by 80%
- Perceived noise by factor of 4 (6 PNdB)
Now, simply put, no-one is going to meet these goals without a paradigm shift in engine technology... so what are the contenders?
It is worth noting, that a reduction of fuel burned during cruise is accompanied by a reduction in CO2 emissions, but rising OPR can
1. The Ultra high bypass ratio turbofan. (UHBPR)
Having a bypass ratio of over 10, this is the closest to current technology, however some serious modifications are still required. Put simply, the
bigger the fan, the slower it must turn, and the turbine speed must be matched to this. There are two means of matching turbine speeds, using triple
shafts (Rolls-Royce) or using a gearbox (Pratt & Whitney).
The geared PW1524G PurePower has been selected as the engines for the Bombardier CSeries. It has a bypass ratio of approximately 13, and Pratt are
targetting fuel savings of 20% relative to the newer A320/737s. Information on the OPR is not yet available.
Current research in the field includes the likes of LeapX, where CFM are targetting similar improvements to the P&W geared turbofan concept.
It is also worth noting Pratt envisages improvements of 1% specific fuel consumption per year, and sees the geared fan as a genuine alternative to the
2. The ducted fan
An evolution of the UHBPR engine, due to further increasing bypass ratio a drastic reduction in bypass nacelle length is required to reduce nacelle
weight to acceptable levels.
The mechanical problems posed are similar to the UHBPR engine.
Pratt & Whitney and NASA were working on an Advanced Ducted Prop (ADP), but the program has been shelved.
3. The Propfan
Seen as the great white hope of many propulsion engineers, even back in the 1980s, experimental propfans could half the fuel consumption relative to
an in-service aircraft (Boeing 767). This is mainly due to a propulsive efficiency of over 80% at cruise Mach numbers (relative to ~65-70% for a
However, propfans are loud, and result in a rise in noise relative to current designs. Current research in the area include 'Clean Sky', in which
Rolls-Royce is a major particpant, as well as the restarting of the old GE36 unducted fan/open rotor research between NASA and general electric.
 Aviation today
 Flight Global
 Forecast International - word document
 Hünecke, K., "Jet Engines: Fundamentals of Theory, Design and Operation", Shrewsbury: Airlife, 1997
 NASA Contractor report 3505 - pdf
 Aviation Week
So now anyone with an interest in Boeing and Airbus' future knows roughly what to hunt for to ascertain where they are heading... if you find
anything of interest, I would greatly appreciate it if you'd post it here!
[edit on 30/6/09 by kilcoo316]