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Bleedless Engines... What Are They?

Tue Nov 01, 2005 1:49 am

So, the title says it all. Bleedless Engines... what are they? What makes them better? (And why doesn't Airbus agree?)

Feel free to get technical - I can take it!
 
CHRISBA777ER
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 2:00 am

IIRC its just an engine that doesnt have a bleed air system from the second stage compressor - which increases the efficiency of the engine.

Bleed air system takes hot air from the compressor and uses it to drive turbines for aircon, cabin pressure, and also heats the leading edges in some types.
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RichardPrice
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 2:00 am

In most engines air is bled from the airflow to run a compressor which provides electrical power and hydraulics pressure. Since this air is used for this purpose, it cant be used for propulsion and hence decreases the engines efficiency.

Bleedless engines dont do this, instead an APU is used or the engine core is used as a generator. This increases the engines efficiency but it also means fuel is used for the APU.

Airbus doesnt necessarily disagree with its usefulness, they just havent been proven to be overall more efficient than an optimal normal engine and the A350s engine, while being a variant of that being used on the 787, is likely to be as efficient due to more development being done on it during the period where the 787 is flying and the A350 isnt.
 
aa777jr
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 2:03 am

Bleedless engines incorporate more electrical, less hydralics. Advantages include energy savings from the use of intelligent actuators, higher reliability through self-diagnosis and prognosis and of course improved engine efficiency due to the decision not to use bleed air from the compressor.

Bleedless engine technologies will be used in developement of Boeings 787 program.

You might wanna ask the same question in Tech/Ops forum, those guys are usually pretty accurate in answering these types of questions.
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PositiveClimb
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 2:17 am

Hi Damon,

I won't get too technical but try to give you an idea. Modern planes have pressurized cabins as you surely know. That means that in flight the cabin pressure is higher than the pressure of the ambient air. So you need a way to produce this higher cabin pressure. Normally on today's aircraft one takes compressed air from the engines, the so-called 'bleed-air'. Common turbofan engines compress the air that enters the engine in several compressor stages. Afterwards, fuel is injected into this now hot and dense air. The ignited fuel/air mixture expands into the turbine section afterwards.
Anyways, before injecting fuel the air is still clean air but it is hotter and denser than the ambient air. This air is taken for pressurizing the cabin (very simply spoken...).

The idea of bleedless engines is to get rid of this (at least in terms of thrust) useless offtake. That would mean that the engine consumes less fuel, as there is no air that has to be compressed without being used for the burning process afterwards. But, of course you need compressed air for the cabin. So the plan is to use electrical driven compressors for compressing the ambient air, which have a very good degree of efficiency when working in their design point. So this can be a way to reduce dissipation losses and therefore to achieve a more fuel efficient system overall.

Best Regards,
Fabian/PositiveClimb Big grin
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prebennorholm
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 3:56 am

"Bleedless engines" is not so much about the engines as about the rest of the plane.

Most planes of today use compressed, hot air from the engine compressor for things like air comditioning and to heat the wing leading edge etc. to avoid ice buildup when flying through clouds. The air taken out of the engine is called "Bleed air".

With bleedless engines those things have to take their energy from somewhere else. On for instance the B787 the idea is to install much more powerful electric power generators and use electricity to power things like air conditioning and leading edge heating.

You could say that by whatever means you take out the energy, you take out the same energy. But that's only half of the truth.

During much of a flight a plane will cruise high up in dry air and need no leading edge heating.

The electric power generators will take out power for heating only when electric heating is switched on.

A bleeded engine has to be designed in such a way that it can cope with various amounts of bleeding. That fact alone tends to sacrifice engine efficiency all the time it is running. Either the compressor delivers too much air to the combustion chambres and turbines, because it is bleeding little, or visa versa.

On a bleedless engine the engine manufacturer can fine tune the whole process better for improved fuel efficiency.

The drawbacks are bigger and heavier electric power generators, slightly more drag for cooling those bigger generators, heavier and more power consuming aircon packs since they will have to do all the cabin pressurization.

But when you calculate pros and cons, then at least Boeing an Gneneral Electric claim that you come out with a gain in the long run. And I don't doubt that they are right.

There may be maintenance and safety issues as well. Leading edge heating is an absulute necessity for safe operation in most parts of the world. It cannot be made simpler and more reliable than just opening a valve and take hot air, which is always there, into tubes in the wing. On the other hand electric systems can also be made totally safe by having redundant systems. How much redundancy is another compromise. More redundancy means increased cost, weight, maintenance etc.

Hope that helps.
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HAWK21M
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 5:36 pm

Apart from the B787,Has Any other Aircraft ever experimented with this type of Technology in the past.
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caboclo
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 6:04 pm

Got to pressurize the cabin, that energy has to come from somewhere. One way or the other the energy comes from jet fuel. Sounds like a minimal savings from bleedless, but with the oil prices the way they are, every little bit helps.
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Loran
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 7:23 pm

This whole process to bleedless engines will take place in conjunction with a redesign of the energy systems. This will move towards more electric and less hydraulic and pneumatic energy supply. Boeing is working on a fuel cell APU system, which provides energy throughout the whole flight envelope, which means the main generators in the engines can be downsized (emergency issues willl require a backup system).
Considering that 10 to 12% of the core stream are used for bleed air and internal cooling, it is from my point of view worth making the step to bleedless technology. It will furhermore reduce the system complexity of the engines, however, as mentioned before it will reuquire some additional (heavier) items for the cabin pressurization equipment.

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Loran
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bri2k1
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 9:40 pm

Quoting Caboclo (Reply 7):
minimal savings

It's hard to quantify from an armchair engineer's perspective. With all the miles and miles of ducting running around an airliner, from the engine bleed air, along the leading edges for anti-ice protection, to the A/C packs and pressurization system, to the other engine(s) for cross-bleed start capability, and linking this all with the APU, there are lots of opportunities for leaks. There's also friction of the air against the sides of the tubing, causing an energy loss. Those two factors aren't present in electrical wiring (or, if they are, they are discovered and repaired quickly). So, it's possible that while the same net energy is required for pressurization, anti-icing, starting, etc., bleedless engines might be able to produce it with a lower gross energy, thus being more efficient.

I may be mistaken, but my understanding of pressurization equipment was that bleed air turned a turbine which turned a compressor that compressed outside air; the engine bleed air itself wasn't actually pumped into the cabing for pressurization. If that's correct, then electrically-powered equipment doesn't need to be much heavier; in lieu of the turbine, a sufficiently-sized electric motor would be installed, and the same effect would be achieved.

My point is, there may be more savings than have been considered here, and ultimately, we may (or may not?) see a greater efficiency increase with bleedless engines.
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PositiveClimb
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RE: Bleedless Engines... What Are They?

Tue Nov 01, 2005 10:19 pm

Quoting Bri2k1 (Reply 9):
There's also friction of the air against the sides of the tubing, causing an energy loss. Those two factors aren't present in electrical wiring (or, if they are, they are discovered and repaired quickly)

Not completely correct. Of course, in electrical wires you don't have the loss of kinetic energy as in air tubes, but don't forget the electrical resistance in the wiring itself. A part of the electrical energy is inevitably converted into heat energy resulting in losses of the (usable) energy.

Quoting Bri2k1 (Reply 9):
I may be mistaken, but my understanding of pressurization equipment was that bleed air turned a turbine which turned a compressor that compressed outside air; the engine bleed air itself wasn't actually pumped into the cabing for pressurization.

No, the bleed air is used directly for cabin pressurization. Of course, it has to be brought to the right pressure level and temperature by restrictor valves and mixers first, but in fact it is the bleed air taken from the compressor section of the engine.

Best Regards,
Fabian/PositiveClimb Big grin
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Jetlagged
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RE: Bleedless Engines... What Are They?

Wed Nov 02, 2005 11:27 am

Quoting RichardPrice (Reply 2):
In most engines air is bled from the airflow to run a compressor which provides electrical power and hydraulics pressure. Since this air is used for this purpose, it cant be used for propulsion and hence decreases the engines efficiency.

Bleed air doesn't provide electrical power on any current engine I've know of (though I vaguely recall the Speys on the Trident might have done it this way). It's usually provided by a mechanically driven generator. Sometimes hydraulic demand pumps are pneumatic (e.g. 747), but the primary hydraulic pumps are usually engine driven or electrically driven.

Quoting PositiveClimb (Reply 4):
But, of course you need compressed air for the cabin.

Not really compressed air, just an air pump. It's not the air pressure that pressurises the cabin but the net air flow into it. Conventional air conditioning packs reduce bleed air pressure and temperature to near the cabin values.

Bleedless engines will save a lot of weight in that the pneumatic ducting from the engines, some of which has to withstand considerable pressure and temperature, will be replaced by electical wiring. The air pumped into the cabin will all be low pressure and low temperature. No need for air cycle machines to cool the hot air either, further saving weight. There's also a safety issue in that a leak from one of these ducts can be damaging to the local structure, and any leak means the duct must be isolated. Electrical offtakes should therefore be more reliable.

Presumably some pneumatic ducting will still be necessary for engine starting purposes. Electric starter motors for engines that size would be excessively heavy.

Current generation engines are designed to produce surplus compressor flow for bleed offtakes. To a certain extent the bleed helps stabilise the engine, so if it's not there the engine might not be able to run so efficiently. Paradoxical but possible nevertheless. So the 787 engines will have to be developed with the bleedless concept in mind.

[Edited 2005-11-02 03:30:59]
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greasespot
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RE: Bleedless Engines... What Are They?

Wed Nov 02, 2005 11:40 am

Your missing the big point......The savings will come from cooler EGT's. when you rob air from the compressor you get an EGT rise. Any time you lower the temp you prolong the life of an engine..a few degrees is a signifigant change with regards to engine life..The single most expensive recurring maintenance cost on an aircraft.

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lightsaber
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RE: Bleedless Engines... What Are They?

Wed Nov 02, 2005 2:51 pm

Quoting Greasespot (Reply 12):
.a few degrees is a signifigant change with regards to engine life..The single most expensive recurring maintenance cost on an aircraft.

50 degrees F is a factor of two in engine life. (Rough "rule of thumb.")

Others have already answered the main topic with justice, so for once I'll have a short post on an engine thread!  bigthumbsup 

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Okie
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RE: Bleedless Engines... What Are They?

Thu Nov 03, 2005 5:04 am

Quoting Jetlagged (Reply 11):
Presumably some pneumatic ducting will still be necessary for engine starting purposes. Electric starter motors for engines that size would be excessively heavy.

Starting the turbines will be with a combination electric starter/alternator.

Boeing met with some resistance on the 787 design from the airlines as the electrical requirements for stand by starting (start cart / ground power source) would have to be purchased (additional capital expenditures) for where the 787 operates for situations where the APU would be MEL'd.

Okie
 
Dougloid
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RE: Bleedless Engines... What Are They?

Thu Nov 03, 2005 6:50 am

I guess I'll just have to wait on this one. I figure it'll be something of a wash. Bleed air systems are pretty much idiot proof at the present time, and they seem to last forever, with the exception of switching valves. Leading edge heating is an area where such could be helpful but my opinion of competing anti ice and deice systems (boots and TKS) leaves me pretty much unimpressed. TKS seems to be OK but when the juice runs out you put it down. Boots are heavy and require regular maintenance. The L1329 had boots and they were a pain in the rear to service-as was TKS for that matter.
Nope, to heat a leading edge you'll be needing quite a supply of current from your generators.
As for the engine stability that bleeding some air off provides my guess is that there'll be a surge bleed valve as there are on a number of turbines.

The real question comes down to this. Are the incremental advantages that will be gained in range through lower fuel consumption going to be enough to offset the price of the technology, both in initial cost and throughout the life of the aircraft (and that includes generators, wires, motors, compressors, starters, heater grids, and ground support equipment).
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
Okie
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RE: Bleedless Engines... What Are They?

Thu Nov 03, 2005 7:45 am

Quoting Dougloid (Reply 15):
The real question comes down to this. Are the incremental advantages that will be gained in range through lower fuel consumption going to be enough to offset the price of the technology, both in initial cost and throughout the life of the aircraft (and that includes generators, wires, motors, compressors, starters, heater grids, and ground support equipment).

Boeing thinks so.

As far as the 787 is concerned it is a matter of installing a lot of the new technology that has evolved a system at a time into a clean sheet airframe to incorporate them all at once.
Electrical resistance heating is one of the most inefficient uses of electricity. However, bleed air is just less efficient but was easy to come by with previous engine technology.

Boeing is looking for a 15%-18% fuel savings.
1. Less fuel to power on board systems.
2. Less aerodynamic drag. (new wing design)
3. Weight, Weight, Weight. (everywhere)

Okie
 
airfoilsguy
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RE: Bleedless Engines... What Are They?

Thu Nov 03, 2005 8:36 am

One thing I think everyone is missing is how are you going to cool the blades and vanes in the "hot" section. This is the section right after ignition that actually reaches temperatures in excess of the pour temp of the components. This is done currently with bleed air forced through the core of the airfoils. Also, I believe some engines currently use bleed air to cool the outside flanges thus ensuring a tight space between the flange and the rotating blades and increased efficiency. I believe for the above reason you will never have a truly bleedless engine.
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Dougloid
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RE: Bleedless Engines... What Are They?

Thu Nov 03, 2005 2:23 pm

Quoting Airfoilsguy (Reply 17):
One thing I think everyone is missing is how are you going to cool the blades and vanes in the "hot" section. This is the section right after ignition that actually reaches temperatures in excess of the pour temp of the components. This is done currently with bleed air forced through the core of the airfoils. Also, I believe some engines currently use bleed air to cool the outside flanges thus ensuring a tight space between the flange and the rotating blades and increased efficiency. I believe for the above reason you will never have a truly bleedless engine.

Most turbine engines I'm familiar with use some internal air for blade and/or vane cooling and they all pretty much use bleed air in a balance piston setup to take up the lion's share of mainshaft thrust. I think the idea of "bleedless" is not drawing it off for tasks that you didn't worry about the cost when Jet A was 20 cents a gallon. They all mostly need some sort of surge bleed valve to prevent compressor stalls particularly on startup.

Somebody's done the math here-I am sure the technology will be interesting.
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Airgypsy
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RE: Bleedless Engines... What Are They?

Wed Nov 09, 2005 11:43 am

Gentlemen,
Go back, way back to pistons. Aircraft were pressurized with very efficient compressors driven by shaft power of several varieties. Big advantage is they could be disengaged for operation when engine power was needed elsewhere. A combination of ram air and compressor would do nicely.

Leaking bleed air systems are a liability. High stage valves are only needed on the ground or very low RPM operations. The main question is "where are they going to get the HEAT?" Hot leading edges keep you flying and cabin heat keeps the PAX from freezing (there is no need for airconditioning at altitude).

The early Spey engine had a very powerful roots type blower for a starter and it could be disengaged from the engine to run the generator if the engine was shut down. It was so loud it had a muffler in the cowling on the BAC1-11.
 
cloudy
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RE: Bleedless Engines... What Are They?

Wed Nov 09, 2005 5:04 pm

Boeing has also said bleedless has the following industrial advantages...

- Pneumatic systems(for our purposes that means systems that use bleed air) have been pushed about as far as they can go. They cannot be made much lighter or more efficient. Electrical systems, on the other hand, are getting more light and efficient all the time.

- Pneumatic systems used in aircraft tend to have a lot of components unique to the aviation industry. Aerospace hardware, for many reasons, is more expensive than most industrial equipment. An electrical replacement, on the other hand, could use technology in wide use in other industries. This could lead to both a cheaper and more reliable system in the long run.

- Having a bleedless engine makes it easier to make the rest of the plane without considering what brand of engine you have. Currently, it is not practical to put a different brand of engine on a plane once it is manufactured and in service. There is simply to much to change. With the 7E7, Boeing hopes to make it possible to simply put on the different engines and swap out some of the plane's software.
 
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lightsaber
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RE: Bleedless Engines... What Are They?

Thu Nov 10, 2005 7:52 am

Quoting Dougloid (Reply 15):
The real question comes down to this. Are the incremental advantages that will be gained in range through lower fuel consumption going to be enough to offset the price of the technology, both in initial cost and throughout the life of the aircraft (and that includes generators, wires, motors, compressors, starters, heater grids, and ground support equipment).

Good question. Boeing thinks the answer is yes. The studies I've seen say currently break even.

Quoting Airfoilsguy (Reply 17):
This is done currently with bleed air forced through the core of the airfoils

Technical point: Bleed air is air pulled off the engine for external use. Thus as you note, "bleedless" means no external CUSTMER bleed. There is no change in the TOBI feeding air to cool the blades. Nor will the Turbine inlet vane fail to get its large chunk of cooling air. The compressor surge vents are already seperate from other bleed systems, so there wouldn't be a need to modify them.

Quoting Cloudy (Reply 20):
- Pneumatic systems used in aircraft tend to have a lot of components unique to the aviation industry. Aerospace hardware, for many reasons, is more expensive than most industrial equipment. An electrical replacement, on the other hand, could use technology in wide use in other industries. This could lead to both a cheaper and more reliable system in the long run.

Ok, this I have to start a rant on.  hissyfit 
Due to the reliability and environmental requirements aerospace components are required to meet, its almost impossible to use non aerospace components. I'm in a program that is trying to use a ton of off the shelf components... ugh. Nightmare. Since current aerospace wiring tends to be custom... I doubt many off the shelf parts will get utilized. Modified off the shelf? yes! Same technology? Yes! But that is already done for aerospace fluid components. e.g., How many styles of solenoid valve can there be? I've seen them from $12 up to over $25,000. The difference is 1) pressure, 2) reliability, 3) vibration resistance (the $12 part broke apart during a vibration test), etc.

Lightsaber
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greasespot
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RE: Bleedless Engines... What Are They?

Thu Nov 10, 2005 12:43 pm

The difference was explaned this way using two firextinguishers.....1 cost 40...the other 400....look exactally the same....The difference with the home one for 40 busks is when you go to use it you HOPE it will work.....With the aircraft one when you go to use it you KNOW it will work....The point being that at 35k feet you need more than hope to keep you safe....

While an aircraft part may look similar to the ground part the fact it the ground one has not been tested to the same extremes...

GS
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trex8
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RE: Bleedless Engines... What Are They?

Sat Nov 12, 2005 10:14 pm

Quoting Okie (Reply 16):
Boeing is looking for a 15%-18% fuel savings.

the 20% savings Boeing likes to quote as the 787s improvement over the 767 is over half due to the inherent increased efficiency from the new generation engines, only something like 3% is due to being bleedless, the rest of the gains is from reduced weight from composites and improved aerodynamics

Quoting Cloudy (Reply 20):
Having a bleedless engine makes it easier to make the rest of the plane without considering what brand of engine you have. Currently, it is not practical to put a different brand of engine on a plane once it is manufactured and in service. There is simply to much to change. With the 7E7, Boeing hopes to make it possible to simply put on the different engines and swap out some of the plane's software.

in reality now that the engineers are actually designing the thing, the entire pylon is specific to each engine type, changing an engine will now require complete removal of the pylon from the wing as well as the engine which will take considerable time and expense. the quick and cheap swap the Boeing salespeople were touting is not going to happen, though it will be easier than previous designs
 
JAXFLL
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RE: Bleedless Engines... What Are They?

Sun Nov 13, 2005 10:22 am

Quoting Trex8 (Reply 23):
in reality now that the engineers are actually designing the thing, the entire pylon is specific to each engine type, changing an engine will now require complete removal of the pylon from the wing as well as the engine which will take considerable time and expense. the quick and cheap swap the Boeing salespeople were touting is not going to happen, though it will be easier than previous designs

It may not be "easy," but it will be easier than an engine replacement. This is important to keep an airlines fleet type the same. If an airline needs aircraft to lease, they can change the pylon/engine and keep the same engine type throughout the fleet. The pylon/engine can then be sold off.

I don't know from first hand knowledge, but there probably aren't that many connections from the pylon to the wing and it probably isn't that big a deal to change.
 
trex8
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RE: Bleedless Engines... What Are They?

Sun Nov 13, 2005 10:48 am

Quoting JAXFLL (Reply 24):
I don't know from first hand knowledge, but there probably aren't that many connections from the pylon to the wing and it probably isn't that big a deal to change.

this issue was discussed in the yahoo orders group and someone quoted an industry article. It will apparently be quite extensive and take even a few days work to do which all means quite expensive. Yes, it will be definitely easier to "swap" than on any other plane previously but it will be far more difficult than a straight engine swap and far more involved and expensive than what Boeing people have been telling the customers till now. While the airline which wants a particular engine will be happy, same article quoted a spokesperson from a leasing company saying something to the efffect of WTH am I going to do with the redundant engines?

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