bralo20
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Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 8:09 am

I've searched but I couldn't find anything here so I'll write a small post about this.


Airbus to begin testing fuel cells for A320

Airbus, a leading manufacturer of aircraft, will be conducting tests on fuel cells to determine how they can be used to reduce fuel consumption and make commercial aircraft more environmentally friendly. The company believes that fuel cells could reduce fuel consumption by as much as 15%. Currently, these plans to test fuel cells will focus on the use of the energy system with an A320 that is owned by the German Aerospace Center. Should the tests prove successful, the aircraft is expected to commence commercial flights in 2015.

Continued story: http://www.hydrogenfuelnews.com/fuel...tch-the-interest-of-airbus/855125/

Belgian source: http://www.flightlevel.be/14168/airb...t-proef-15-minder-kerosineverbruik (Dutch)
 
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Aquila3
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 8:59 am

I wonder where all those savings will come from.
The only use that I can see for now are:

1)Replacement of existing, heavy, Lead-Acid batteries (if any).

2)Power supply for an electric motor for taxiing , eventually helping during T/O run, with eventual energy recover during landing.

I do not see them of any use for the main power plant, since the size of it will probably forbid any kind of additional electric motor+battery system due to weight considerations, at least if the traditional Turbofan is still kept . But maybe I am not up-to date.
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jox
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 9:34 am

What about using them to power all the auxilary hyudralics, compressors, generators etc etc? Thus removing the need for extra gearboxes etc from the main engines. I.e make the use of the main (tubofan) enginges purely for propulsion of the aircraft. Would that save enough fuel to make sense?
 
StickShaker
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 9:58 am

Taken from the article ...

.... The 90-kilowatt fuel cell will serve as an auxiliary energy source for the plane’s entertainment systems, lighting, and environment control systems .....

I realise that this is just a pilot project but I don't see much of a saving when you compare the 90kw output of the fuel cell to the combined thrust of the 2 CFM/V2500 engines on the 320, if that 90kw is intended to grow then what is the eventual target size ?
Do "environmental control systems" include air conditioning ?
How much weight is added by the fuel cell and what are the various issues involved in storing Hydrogen on a commercial airliner and what complexities are added to refuelling and turn around times on the ground ?
Would the fuel cell effectively replace the APU ?
It doesn't seem to be bolt-on technology - it brings a whole range of baggage along with it.

I can see the benefits of fuel cells in ground transport (cars, trucks) and marine transport (ships) as the fuel cell can completely replace the internal combustion engine. We won't see turbines being replaced on commercial aircraft that need to travel at around 500 knots as there is just no substitute for that level of chemical energy.
I would have thought that Boeing's 787 electric architecture was a more elegant solution.


Regards,
StickShaker

[Edited 2012-08-08 03:03:04]
 
r2rho
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 11:24 am

Quoting StickShaker (Reply 3):
Would the fuel cell effectively replace the APU ?

That is the only use I can see for it, yes.

Quoting jox (Reply 2):
What about using them to power all the auxilary hyudralics, compressors, generators etc etc? Thus removing the need for extra gearboxes etc from the main engines. I.e make the use of the main (tubofan) enginges purely for propulsion of the aircraft. Would that save enough fuel to make sense?

Sure, but those are all flight-critical systems, you cannot power them from a secondary power source, let alone an immature technology. A primary power source - which for the foreseeable future will be turbine engines (GTF, OR or whatever) - will still have to provide power to any safety critical systems. But if a fuel cell can take off some load from the generators for non-critical systems, while not adding weight nor maintenance complexity, the fuel savings (likely to be mid single-digits) will be welcome. And less airport noise too.

Quoting StickShaker (Reply 3):
It doesn't seem to be bolt-on technology - it brings a whole range of baggage along with it.

It is not bolt-on at all, particularly if you want to take full advantage of the fuel cell's capabilities and not just directly replace the APU. Fuel cells produce as byproducts water, which on the Space Shuttle was used as drinking water, as well as oxygen depleted air, which could be used for fuel tank inerting. But to take advantage of that, you have to rethink the layout of your inerting and water waste systems. That is definitely not "plug&play".

In any case it's worth starting to move from pure research to actual testing of prototypes and demonstrators, this is a technology for the long run.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 11:29 am

Quoting StickShaker (Reply 3):
Do "environmental control systems" include air conditioning ?

Yes.


Gruß, masi1157
 
tdscanuck
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 1:21 pm

Quoting Aquila3 (Reply 1):
I wonder where all those savings will come from.

Getting rid of the APU.

Quoting Aquila3 (Reply 1):
1)Replacement of existing, heavy, Lead-Acid batteries (if any).

I think most aircraft have been on Ni-Cad or Li technology for a while now.

Quoting Aquila3 (Reply 1):
2)Power supply for an electric motor for taxiing , eventually helping during T/O run, with eventual energy recover during landing.

A fuel cell won't help with energy recovery; they don't backdrive well.

Quoting jox (Reply 2):
What about using them to power all the auxilary hyudralics, compressors, generators etc etc? Thus removing the need for extra gearboxes etc from the main engines. I.e make the use of the main (tubofan) enginges purely for propulsion of the aircraft. Would that save enough fuel to make sense?

Actually removing the gearbox would require huge engine redesign; the EEC power supply, the fuel pump, and the oil pump all run off the gearbox. And once you the gearbox to run those required components, adding other stuff like the generators has low overhead.

Quoting StickShaker (Reply 3):
I realise that this is just a pilot project but I don't see much of a saving when you compare the 90kw output of the fuel cell to the combined thrust of the 2 CFM/V2500 engines on the 320

You're comparing to the wrong thing; compare to the 90 kW APU.

Quoting StickShaker (Reply 3):
Do "environmental control systems" include air conditioning ?

Yes, as well as the air distribution system (fans, ducts, heaters, etc.).

Quoting StickShaker (Reply 3):
How much weight is added by the fuel cell and what are the various issues involved in storing Hydrogen on a commercial airliner and what complexities are added to refuelling and turn around times on the ground ?

They're just using hydrogen now for test reasons; it's relatively easy to crack jet fuel into hydrogen on demand, especially if you use the higher temperature technologies like solid oxide.

Quoting StickShaker (Reply 3):
Would the fuel cell effectively replace the APU ?

That's the plan.

Quoting StickShaker (Reply 3):
It doesn't seem to be bolt-on technology - it brings a whole range of baggage along with it.

True, but it gets rid of a whole other range of baggage associated with the APU. Among other things, APU's are *extremely* difficult to design because they have such a huge start envelope.

Quoting r2rho (Reply 4):
A primary power source - which for the foreseeable future will be turbine engines (GTF, OR or whatever) - will still have to provide power to any safety critical systems

There's no reason it has to be a turbine; it just has to be as reliable as a turbine. Fuel cells, with no moving parts in the primary power path, are incredibly reliable. It's like the difference between relays and solid state electronics. Moving parts are bad for reliability.

Tom.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 1:48 pm

Quoting tdscanuck (Reply 6):

Thanks for your concise replies Tom.

Quoting tdscanuck (Reply 6):
Quoting StickShaker (Reply 3):How much weight is added by the fuel cell and what are the various issues involved in storing Hydrogen on a commercial airliner and what complexities are added to refuelling and turn around times on the ground ?
They're just using hydrogen now for test reasons; it's relatively easy to crack jet fuel into hydrogen on demand, especially if you use the higher temperature technologies like solid oxide.

I'm a bit confused here - is the intention to generate hydrogen from cracking jet fuel while in the air (a flying oil refinery) as opposed to storing liquid hydrogen aboard the aircraft ?

Quoting tdscanuck (Reply 6):
Quoting StickShaker (Reply 3):I realise that this is just a pilot project but I don't see much of a saving when you compare the 90kw output of the fuel cell to the combined thrust of the 2 CFM/V2500 engines on the 320
You're comparing to the wrong thing; compare to the 90 kW APU.

OK, got that - but how could replacing a 90kw APU generate as much as 15% in fuel savings over current configurations ?


Regards,
StickShaker
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 6:29 pm

Quoting StickShaker (Reply 7):
OK, got that - but how could replacing a 90kw APU generate as much as 15% in fuel savings over current configurations ?

That 15% may be a fully integrated system design. Actually completely remove electrical power duties from the engines saving both weight of the gearbox plus the drag of the generation+gearbox. ie, the engines only provide thrust, the fuel cells would be responsible for everything including engine electronics, hydraulics, etc. The net result would be streamlined engine designs with all electrical power handled by much higher efficiency systems than parasitic gearboxes driving generators.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 7:59 pm

Quoting tdscanuck (Reply 6):
They're just using hydrogen now for test reasons; it's relatively easy to crack jet fuel into hydrogen on demand, especially if you use the higher temperature technologies like solid oxide.

So you could generate hydrogen? Is that process endothermic or exothermic, do you know? What is done with the excess carbon?

Quoting r2rho (Reply 4):
It is not bolt-on at all, particularly if you want to take full advantage of the fuel cell's capabilities and not just directly replace the APU. Fuel cells produce as byproducts water, which on the Space Shuttle was used as drinking water, as well as oxygen depleted air, which could be used for fuel tank inerting. But to take advantage of that, you have to rethink the layout of your inerting and water waste systems. That is definitely not "plug&play".

You could keep the waste water, but I think it would make more sense to dump it overboard. I don't think that the amount produced would be very large, and since aircraft don't fly multi-day missions like the Shuttle did, there isn't a pressing need to collect that water. To collect the water and put it into the fresh-water storage would require a whole new system of pipes and filters, and that adds expense, weight, and maintenance.
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 8:04 pm

Quoting StickShaker (Reply 7):
I'm a bit confused here - is the intention to generate hydrogen from cracking jet fuel while in the air (a flying oil refinery) as opposed to storing liquid hydrogen aboard the aircraft ?

In the future, I expect them to go to cracking the jet fuel on demand (it's a lot simpler than a refinery). For test purposes, I'd completely assume an H2 tank because it's so much simpler from a system standpoint. Baby steps.

Quoting StickShaker (Reply 7):
OK, got that - but how could replacing a 90kw APU generate as much as 15% in fuel savings over current configurations ?

They're either talking just about APU burn or, if they really do mean overall burn, they must be moving almost the entire auxiliary load off the engines. Fuel cell's don't use a thermodynamic cycle so they don't have to obey Carnot efficiency limits. But even then, getting 15% *overall* seems really unlikely to me.

Tom.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 8:04 pm

Quoting spink (Reply 8):
The net result would be streamlined engine designs with all electrical power handled by much higher efficiency systems than parasitic gearboxes driving generators.

Would that also make the system more reliable?
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 8:09 pm

Quoting tdscanuck (Reply 6):
They're just using hydrogen now for test reasons; it's relatively easy to crack jet fuel into hydrogen on demand, especially if you use the higher temperature technologies like solid oxide.

Would that not totally destroy the point?

NS
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Wed Aug 08, 2012 9:15 pm

Quoting gigneil (Reply 12):
Would that not totally destroy the point?

I know that for combustion, H2 provides the highest energy per WEIGHT (but not per volume). A fuel cell is basically a very controlled combustion. The thing is that the energy is removed in the form of electron movement, rather than heat, so the efficiency can be much higher. A really good jet engine might have a thermodynamic efficiency of 25-30% while a fuel cell could be as high as 60% depending on a number of factors. So if a fuel cell can produce as much power as an APU while using half the fuel, then it certainly would help.

That said, if the improvement in efficiency is 100%, in order for this to result in a 15% reduction in fuel burn, the APU would have to be responsible for 30% of overall trip fuel burn on a typical mission and I don't think that's even remotely the case.
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 12:36 am

What I'm saying is that cracking jet fuel to make hydrogen sorta kills the point - since my guess is that the cracking the fuel to make the hydrogen is less efficient than just burning it.

Also, the other point is that hydrogen is the most abundant element in the universe. It comes from places far easier to obtain than jet fuel, which is relatively quite rare - particularly in nature.

NS
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 2:10 am

Quoting DocLightning (Reply 9):
Quoting tdscanuck (Reply 6):
They're just using hydrogen now for test reasons; it's relatively easy to crack jet fuel into hydrogen on demand, especially if you use the higher temperature technologies like solid oxide.

So you could generate hydrogen? Is that process endothermic or exothermic, do you know?

I believe it's endothermic; elemental hydrogen is highly reactive so it probably takes energy to break it off the hydrocarbon. But I'm not positive about that. If it is endothermic you've got plenty of carbon around to combust to get the required energy.

Quoting DocLightning (Reply 9):
What is done with the excess carbon?

Overboard as CO2.

Quoting gigneil (Reply 12):
Quoting tdscanuck (Reply 6):
They're just using hydrogen now for test reasons; it's relatively easy to crack jet fuel into hydrogen on demand, especially if you use the higher temperature technologies like solid oxide.

Would that not totally destroy the point?

That depends on what "the point" is. Fuel cells are more than efficient enough to make up the energy delta in cracking the fuel.

Quoting DocLightning (Reply 13):
A fuel cell is basically a very controlled combustion.

It chemically resembles combustion but it doesn't generate any heat, which is the big difference (as you noted).

Quoting gigneil (Reply 14):
What I'm saying is that cracking jet fuel to make hydrogen sorta kills the point - since my guess is that the cracking the fuel to make the hydrogen is less efficient than just burning it.

Cracking and fuel cell reduction are both very efficient processes. Burning is also very efficient in terms of liberating energy, but attempting to extract mechanical energy via a heat engine is inefficient and what screws you. Fuel cells get around that by not being heat engines.

Quoting gigneil (Reply 14):
Also, the other point is that hydrogen is the most abundant element in the universe. It comes from places far easier to obtain than jet fuel, which is relatively quite rare - particularly in nature.

An airplane is already full of jet fuel; that's pretty easy to obtain. Adding a new high pressure or cryogenic fuel system and a whole new set of fueling infrastructure...not so much.

Tom.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 2:20 am

Quoting tdscanuck (Reply 10):
Quoting StickShaker (Reply 7):I'm a bit confused here - is the intention to generate hydrogen from cracking jet fuel while in the air (a flying oil refinery) as opposed to storing liquid hydrogen aboard the aircraft ?
In the future, I expect them to go to cracking the jet fuel on demand (it's a lot simpler than a refinery). For test purposes, I'd completely assume an H2 tank because it's so much simpler from a system standpoint. Baby steps.

This entire process doesn't sound particularly elegant or simple. Current aircraft generate all required energy from one chemical process - the combustion of jet fuel in the turbofans. Using a fuel cell powered by cracking jet fuel effectively expands that to 3 chemical processes of which 2 are solely for the purpose of replacing a 90kw APU. All of these chemical processes will require monitoring and a high degree of automation to operate successfully in an aviation environment.
How do you guarantee reliability and provide adequate redundancy for such a complex system - what do you do when your fuel cracker or fuel cell goes AWOL at 35,000 ft given that the turbofans now cannot produce any electrical power ?
How do you satisfy the number of electrical power sources required for ETOPS operations ?
Can you provide the required redundancy without your aircraft resembling the next manned mission to Mars ?

Quoting gigneil (Reply 14):
What I'm saying is that cracking jet fuel to make hydrogen sorta kills the point - since my guess is that the cracking the fuel to make the hydrogen is less efficient than just burning it.

What is the input cost in terms of energy to operate such a fuel cracker - you couldn't afford much given you are only saving 90kw.

I'm playing the devil's advocate here but I'm also struggling with such a complex solution to a relatively simple issue. No doubt Airbus know what they are doing but I cant see fuel cells being the best way to go.


Regards,
StickShaker

[Edited 2012-08-08 19:48:24]

[Edited 2012-08-08 19:49:01]
 
XT6Wagon
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 2:56 am

Quoting StickShaker (Reply 16):
I'm playing the devil's advocate here but I'm also struggling with such a complex solution to a relatively simple issue. No doubt Airbus know what they are doing but I cant see fuel cells being the best way to go.

yah, it seems 581% stupid till the APU got mentioned. Thats the ONLY item on a plane I could see being replaced by a fuel cell. Only you have to prove the fuel cell in the operating enviroment before any sane regulating agency today would allow you to replace the APU with one.
 
tdscanuck
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 3:09 am

Quoting StickShaker (Reply 16):
Using a fuel cell powered by cracking jet fuel effectively expands that to 3 chemical processes of which 2 are solely for the purpose of replacing a 90kw APU. All of these chemical processes will require monitoring and a high degree of automation to operate successfully in an aviation environment.

Crackers are dead simple. In the ultimate end state, you use a solid oxide fuel cell. They run so hot that the hydrocarbon fuel decomposes on its own (you can use a catalyze to lower the temperature). The fuel cell reacts the hydrogen with atmospheric oxygen directly into electricity; the carbon reacts with atmospheric oxygen to maintain the fuel cell temp and goes overboard as CO2. No extra parts, no monitoring, no automation. It's absurdly simple relative to, say, an APU.

Quoting StickShaker (Reply 16):
How do you guarantee reliability and provide adequate redundancy for such a complex system - what do you do when your fuel cracker or fuel cell goes AWOL at 35,000 ft given that the turbofans now cannot produce any electrical power ?
How do you satisfy the number of electrical power sources required for ETOPS operations ?
Can you provide the required redundancy without your aircraft resembling the next manned mission to Mars ?

I don't think anyone's seriously suggesting removing electrical generating capability from the engines (the engine OEMs would never got for that, for one thing). If you had a good reliable fuel cell for primary power, however, you could greatly reduce the generator load on the engines down to just that necessary for flight-critical loads. That would shave, at least, 50% off the required engine generator capacity.

Quoting StickShaker (Reply 16):
What is the input cost in terms of energy to operate such a fuel cracker - you couldn't afford much given you are only saving 90kw.

Zero in terms of the aircraft; the energy you need comes from the carbon in the fuel.

Quoting XT6Wagon (Reply 17):
Only you have to prove the fuel cell in the operating enviroment before any sane regulating agency today would allow you to replace the APU with one.

Which is why Boeing is running a fuel cell on their 737 ecoDemonstrator right now:
http://www.aviationweek.com/Article....e-xml/awx_07_11_2012_p0-475289.xml

They're only using it to power the galley, so far, but baby steps...

Tom.
 
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lightsaber
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 3:15 am

I believe long term fuel cells will be the primary power source on aircraft. They are that much more efficient than gas turbines. Even with the losses to transmit the power to a ducted propeller.

However it will take a high pressure fuel cell to achieve the power density at an acceptable weight for aircraft. High pressure=high performance which means *expensive* development bills (a la today's gas turbines). So baby steps are required. I applaud the idea of in flight auxiliary power. However, since an aircraft requires 3 to 4 power sources. (The 4th power source reduces the required redundancy in other systems.)

A jet-A cracked fuel cell will probably be the long term path. But that will require weight and volume of the equipment. Such as a BWB.    The fuel savings will provide the weight and volume in that sort of design.

But this is a very long term solution.

Where I receive my graduate degree for gas turbine related research also hosts the national fuel cell center. Same professor... So I have the benefit of being exposed to both. I find it interesting that the two are complimentary. A compressor will be required to compress the gas into the fuel cell and since there will be a volumetric expansion, why not put a turbine on the exhaust to power that compressor? In the long run, the fuel cell becomes a *large* combustor replacement for a gas turbine. However, do to the volume of the *future* fuel cells, I expect them to be in the aircraft body or BWB wing with the propulsor separate, powered by electricity.

Quoting Bralo20 (Thread starter):
The company believes that fuel cells could reduce fuel consumption by as much as 15%.

That sounds ok for small units. Long term, I expect more like a 30% fuel burn reduction compared to *future* gas turbines. But we're talking 2030 to 2040 time frames *at the earliest.*

Quoting StickShaker (Reply 3):
if that 90kw is intended to grow then what is the eventual target size ?

It will take money to grow. Having an in service application will provide those funds.

Quoting tdscanuck (Reply 15):
Fuel cells are more than efficient enough to make up the energy delta in cracking the fuel.

   There are ways to stage a fuel cell so the cracking is in a fuel cell, just a much cruder/less efficient type of fuel cell than the one that will generate most of the power.

Quoting StickShaker (Reply 16):
what do you do when your fuel cracker or fuel cell goes AWOL at 35,000 ft given that the turbofans now cannot produce any electrical power ?

Not happening. Again, aircraft require triple to quadruple power supplies (for 100+ seats). No one is going to go that far to fuel cells that quickly. There will be gearboxes on the engines for decades.

Quoting tdscanuck (Reply 15):
It chemically resembles combustion but it doesn't generate any heat, which is the big difference (as you noted)

Nitpick: Theoretically doesn't generate heat. The reality is different. They are not as hot as a gas turbine exhaust by any means, but fuel cells are no where near their theoretical efficiency. They won't ever be. A super efficient fuel cell will be large. For example, a land based power generating gas turbine is far more efficient than an airborne gas turbine. But no one is putting a bottoming cycle onto a 787/A380.    There is always a trade between efficiency and size/weight and aircraft will have to error towards smaller packages.

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thegeek
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 3:25 am

Quoting tdscanuck (Reply 15):
An airplane is already full of jet fuel; that's pretty easy to obtain. Adding a new high pressure or cryogenic fuel system and a whole new set of fueling infrastructure...not so much.

Playing devils advocate, you would need pipe work from the wing tanks to the rear of the plane, assuming the APU remains there. That adds weight, maintenance and is a hazard. Of course, a compressed hydrogen tank is a hazard too, but if it fits into space in the tail not otherwise used, then its low density is not an issue.

Having a second type of fuel on board would be a real hassle at airports when it comes time to refuel - but for a long range wide body, this point is less important.

For the record, I expect you are correct but I thought I'd put these points out there.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 4:02 am

Quoting tdscanuck (Reply 18):
I don't think anyone's seriously suggesting removing electrical generating capability from the engines (the engine OEMs would never got for that, for one thing). If you had a good reliable fuel cell for primary power, however, you could greatly reduce the generator load on the engines down to just that necessary for flight-critical loads. That would shave, at least, 50% off the required engine generator capacity.
Quoting lightsaber (Reply 19):
Not happening. Again, aircraft require triple to quadruple power supplies (for 100+ seats). No one is going to go that far to fuel cells that quickly. There will be gearboxes on the engines for decades.

OK, thanks for that guys. But if the gearbox is still going to be there (albeit with lighter loads) is it still plausible to get 15% in fuel savings ?

One last question - is there any way that fuel cell technology could leverage the all electric architecture that Boeing has just developed (so it won't go to waste).


Regards,
StickShaker
 
thegeek
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 4:47 am

Quoting StickShaker (Reply 21):
OK, thanks for that guys. But if the gearbox is still going to be there (albeit with lighter loads) is it still plausible to get 15% in fuel savings ?

I think it's been mentioned above that the 15% savings are thought to be savings in APU fuel consumption.

Quoting StickShaker (Reply 21):
One last question - is there any way that fuel cell technology could leverage the all electric architecture that Boeing has just developed (so it won't go to waste).

Yes, of course. While you still need the full size generators in the engines for redundancy purposes, you could just turn them off.

The problem with that might be that at cruise you are underloading the turbines even more severely. Turning off the fuel cell would load up the turbines more and increase the efficiency of the engines. Whether or not this would counteract the higher efficiency of the fuel cell, I'm not sure.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 5:41 am

Quoting tdscanuck (Reply 15):
I believe it's endothermic; elemental hydrogen is highly reactive so it probably takes energy to break it off the hydrocarbon. But I'm not positive about that. If it is endothermic you've got plenty of carbon around to combust to get the required energy.

Yes, but that burns fuel, which is what you are trying not to do. So now the cell has to be able to make up for the cracking energy, too. How much energy is needed to crack? I suppose you could just feed it into one of the high-temp ones, but now insulation becomes an issue, since you're dealing with 600C+ temps.

Quoting thegeek (Reply 22):
The problem with that might be that at cruise you are underloading the turbines even more severely. Turning off the fuel cell would load up the turbines more and increase the efficiency of the engines. Whether or not this would counteract the higher efficiency of the fuel cell, I'm not sure.

You could design the engines to operate most efficiently with the generators off. If the idea was to use the fuel cell to provide all on-board electrical demand and use the turbines only for thrust generation.

Quoting lightsaber (Reply 19):
I believe long term fuel cells will be the primary power source on aircraft. They are that much more efficient than gas turbines. Even with the losses to transmit the power to a ducted propeller.

The big problem is the size of sufficiently powerful electric motors. This is a submarine electric drive unit (all submarines are fundamentally electric, whatever generates the electricity), which must have a similar power output to a commercial turbofan.

http://farm4.static.flickr.com/3424/3768921932_497f69c334_o.jpg
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 6:06 am

Quoting DocLightning (Reply 23):
You could design the engines to operate most efficiently with the generators off. If the idea was to use the fuel cell to provide all on-board electrical demand and use the turbines only for thrust generation.

I'm not convinced. The problem with cruise is that the engines are under-loaded. Removing the electrical load is sure to make this worse.

Quoting DocLightning (Reply 23):
The big problem is the size of sufficiently powerful electric motors. This is a submarine electric drive unit (all submarines are fundamentally electric, whatever generates the electricity), which must have a similar power output to a commercial turbofan.

No, most nuclear subs have direct drive. The French "Rubis" class is an exception. There could be others.
 
spink
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 9:52 am

Quoting StickShaker (Reply 16):
This entire process doesn't sound particularly elegant or simple. Current aircraft generate all required energy from one chemical process - the combustion of jet fuel in the turbofans. Using a fuel cell powered by cracking jet fuel effectively expands that to 3 chemical processes of which 2 are solely for the purpose of replacing a 90kw APU. All of these chemical processes will require monitoring and a high degree of automation to operate successfully in an aviation environment.

Actually, a fuel cell is much more simple and elegant than a fanjet engine. It is a chemical/electrical design instead of a chemical/electrical/thermal/mechanical design.

Quoting StickShaker (Reply 16):
How do you guarantee reliability and provide adequate redundancy for such a complex system - what do you do when your fuel cracker or fuel cell goes AWOL at 35,000 ft given that the turbofans now cannot produce any electrical power ?
How do you satisfy the number of electrical power sources required for ETOPS operations ?
Can you provide the required redundancy without your aircraft resembling the next manned mission to Mars ?

The inherent reliability and reliability wear metrics should be much better than for a jet engine or an APU. In addition, you would do it how it has always been done when 5 9's or better are required: N+X redundancy.

Quoting StickShaker (Reply 16):
What is the input cost in terms of energy to operate such a fuel cracker - you couldn't afford much given you are only saving 90kw.

Rather minimal in comparison to efficiency difference between a fuel cell and a parasitic gear/generator system attached to a propulsion jet turbine.

Quoting StickShaker (Reply 16):
I'm playing the devil's advocate here but I'm also struggling with such a complex solution to a relatively simple issue. No doubt Airbus know what they are doing but I cant see fuel cells being the best way to go.

Actually, a fuel cell is a rather simple solution to the rather complex way it is currently done. Yes, the fuel cell itself is higher technology than a parasitic gear-generator system but that doesn't mean it is more complex.

Quoting tdscanuck (Reply 18):
I don't think anyone's seriously suggesting removing electrical generating capability from the engines (the engine OEMs would never got for that, for one thing). If you had a good reliable fuel cell for primary power, however, you could greatly reduce the generator load on the engines down to just that necessary for flight-critical loads. That would shave, at least, 50% off the required engine generator capacity.

Why not remove the electrical generation capability from the engines. It allows for a simpler engine design. All the manufacturers would have to do is specify the electric input requirements for the engine.

Quoting thegeek (Reply 20):
Playing devils advocate, you would need pipe work from the wing tanks to the rear of the plane, assuming the APU remains there. That adds weight, maintenance and is a hazard. Of course, a compressed hydrogen tank is a hazard too, but if it fits into space in the tail not otherwise used, then its low density is not an issue.

The pipework already exists in order to feed the APUs, so there is no difference there.

Quoting DocLightning (Reply 23):
The big problem is the size of sufficiently powerful electric motors. This is a submarine electric drive unit (all submarines are fundamentally electric, whatever generates the electricity), which must have a similar power output to a commercial turbofan.

The actual electric motors can be made smaller but aren't because the cost factors vs weight/volume for most applications don't support it (there is a lot of area to play with). It should be possible to more than halve the volume of the electric motors using modern high end materials and methods. Realistically it should be possible to stuff ~25MW of electric motor in a 1-1.5m radius.
 
sweair
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 10:29 am

At 2500C H2O cracks into H2 and O2 on its own, no one has yet found materials that would survive this temperature. Most current H2 is hydroreformed from natural gas.
 
StickShaker
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 2:21 pm

Quoting spink (Reply 25):
Actually, a fuel cell is much more simple and elegant than a fanjet engine. It is a chemical/electrical design instead of a chemical/electrical/thermal/mechanical design.
Quoting spink (Reply 25):
Actually, a fuel cell is a rather simple solution to the rather complex way it is currently done. Yes, the fuel cell itself is higher technology than a parasitic gear-generator system but that doesn't mean it is more complex.

The fuel cell itself may be an elegant entity but the need to store (and refuel) liquid hydrogen on board an aircraft is not. I see fuel cracking in much the same light - an elegant process in itself but not quite as elegant once placed in an aviation environment.


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StickShaker
 
abba
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 2:59 pm

Quoting tdscanuck (Reply 18):
It's absurdly simple relative to, say, an APU.



Sure - here is an example of how its works. It states that the cell can be powered by many different forms of fuel.
http://www.topsoefuelcell.com/
 
tdscanuck
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 5:56 pm

Quoting thegeek (Reply 20):
Playing devils advocate, you would need pipe work from the wing tanks to the rear of the plane, assuming the APU remains there. That adds weight, maintenance and is a hazard.

Why would you add another pipe? Use the one that's already there...no extra weight, no extra maintenance, no new hazard.

Quoting thegeek (Reply 20):
Of course, a compressed hydrogen tank is a hazard too, but if it fits into space in the tail not otherwise used, then its low density is not an issue.

The weight of the fuel isn't much of an issue; the weight of the tank is a huge issue. There's also a huge issue with containment and fire suppression.

Quoting StickShaker (Reply 21):
But if the gearbox is still going to be there (albeit with lighter loads) is it still plausible to get 15% in fuel savings ?

It all depends...we're still not sure what the "15%" is relative to.

Quoting StickShaker (Reply 21):
One last question - is there any way that fuel cell technology could leverage the all electric architecture that Boeing has just developed (so it won't go to waste).

Yes, very much so. Once you get off bleed air (which implies mechanical prime movers) you open up a huge range of options for switching, routing, and redundancy. Switches and transformers are far more flexible and robust than valves, regulators, and shafts.

Quoting DocLightning (Reply 23):
Yes, but that burns fuel, which is what you are trying not to do. So now the cell has to be able to make up for the cracking energy, too. How much energy is needed to crack?

Cracking burns fuel that you weren't going to use anyway (the C in the hydrocarbon...the fuel cell can only use the H). It's "free" from an overall system standpoint.

Quoting DocLightning (Reply 23):
The big problem is the size of sufficiently powerful electric motors. This is a submarine electric drive unit

Submarines have totally different trade space; they don't like gearboxes so they go for direct-drive motors, which have to be huge to generate the required torque. They also don't care about weight. A 100kW aviation electric motor is smaller than a loaf of bread (smaller than the equivalently powerful turbine, actually). 100kW is a long way from what you need for primary propulsion, but the point is that all motors are no created equal.

This is also a big reason behind the shift to all-electric architecture on the 787...the efficiency of pneumatic-to-mechanical systems has pretty much plateaued. Thanks to developments across a lot of industries, the efficiency and power density of electrical systems is going up rapidly (thank you, hybrid cars). The future upside on electrical systems is much larger.

Quoting spink (Reply 25):
Why not remove the electrical generation capability from the engines. It allows for a simpler engine design. All the manufacturers would have to do is specify the electric input requirements for the engine.

Because it violates one of the most basic design assumptions of how aviation powerplants work; they should continue to run absent *all* inputs from the airplane other than fuel. The engine should be able to bootstrap itself in flight (i.e. as long as you can feed it fuel it should be able to start and run). It does not have to be this way, obviously, but to do otherwise would be a huge change in the level of integration between the engine and the airframe; I can already see the regulator's and engine OEM's heads exploding.

Also, you need to be able to start the engine on the ground, which means you need a big motor of some kind (pneumatic, electric, etc.). If you already have an electric starter, you have a "free" generator so you might as well use it.

Quoting StickShaker (Reply 27):
The fuel cell itself may be an elegant entity but the need to store (and refuel) liquid hydrogen on board an aircraft is not.

That's why you crack jet fuel; no need to store hydrogen at all.

Quoting StickShaker (Reply 27):
I see fuel cracking in much the same light - an elegant process in itself but not quite as elegant once placed in an aviation environment.

A fuel cracker is far simpler than, say, the fuel management unit on an APU. The total complexity drops way down when you don't have high-speed moving parts and fire involved.

Tom.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 6:22 pm

Quoting r2rho (Reply 4):
Sure, but those are all flight-critical systems, you cannot power them from a secondary power source, let alone an immature technology.

Why would powering the flight-critical systems be exclusive to the fuel cell? What would be the problem with using the fuel cell for critical components with the engines as a backup to be used when necessary?

Quoting tdscanuck (Reply 29):
Quoting thegeek (Reply 20):
Playing devils advocate, you would need pipe work from the wing tanks to the rear of the plane, assuming the APU remains there. That adds weight, maintenance and is a hazard.

Why would you add another pipe? Use the one that's already there...no extra weight, no extra maintenance, no new hazard.

Why would the fuel cell need to be in the tail of the plane where the APU is currently? Does a fuel cell make a lot of noise and/or require a large exhaust vent?
 
tdscanuck
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Thu Aug 09, 2012 7:29 pm

Quoting D L X (Reply 30):
Why would the fuel cell need to be in the tail of the plane where the APU is currently? Does a fuel cell make a lot of noise and/or require a large exhaust vent?

Ooooh, good point. Hadn't thought of that. Fuel cells are nearly silent (if you hear anything it's the pumps and fans, not the fuel cell itself). They do need a lot of air (so big intake and exhaust) but that's something you already have readily available in the wing-to-body fairing to support the ECS system.

Tom.
 
thegeek
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 12:05 am

Quoting spink (Reply 25):
The pipework already exists in order to feed the APUs, so there is no difference there.

Right. Not sure how I forgot that.

Quoting D L X (Reply 30):
Why would the fuel cell need to be in the tail of the plane where the APU is currently? Does a fuel cell make a lot of noise and/or require a large exhaust vent?

Might I suggest that putting it where the centre fuel tank is would rob some fuel tankage? Perhaps you could put it in the crown space, but then you need ducts for the air and the exhaust to reach it.
 
prebennorholm
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 1:09 am

15% ....... 90kw .......

The numbers simply don't add up in any way.

The most popular Airbus plane, the 320, takes off on some 50 Mw power. It cruises on much less, about a dozen Mw or such. 90 kw is 0.75% of 12 Mw, not 15%.

A fuel cell has its name for a reason. It consumes fuel to generate power. It is potentially much more efficient, maybe as much as three times more efficient when using hydrogen, but still it it spends fuel. Save 2/3 of the 0.75%, and we have saved 0.5%.

I have seen proposed on this thread that we generate hydrogen from jet fuel, spending the carbon on the cracking. Honestly, can we imagine a coal dust fire to power a small refinery cracker on a jet plane? Maybe? But I may be just too old to imagine that. Or maybe because I have spent my whole career in the oil business and have learned a little about refinery processes and the power they need. But in any case that would waste the energy from the carbon, subtracting further from the potential 0.75% to well below 0.5% saving.

We are constantly circling around replacing the APU. That makes sense since the 90 kw figure fits pretty well. But the problem here is, when did we last time hear an APU actually running? Well, aircraft mechanics do hear them when they test them after maintenance work, and they do get started with intervals during long range ETOPS flights to make sure that power redundancy is still there.

There sure still is an airport out there without standard ground power. I just don't see them that often. The nearest commercial airport to where I am typing this post is as small as small can be: Two B733 operations per day. The ramp guy is always ready with ground power before the last engine is shut down, no APU is used. I haven't heard an APU running during the last decade while at the same time visiting airports in a dozen countries, some of them many times.

We can't save fuel on exchanging the APU with a more efficient power source when the APU is hardly ever used in the first place.

The numbers don't add up.
Always keep your number of landings equal to your number of take-offs
 
tdscanuck
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 1:16 am

Quoting prebennorholm (Reply 33):
I have seen proposed on this thread that we generate hydrogen from jet fuel, spending the carbon on the cracking. Honestly, can we imagine a coal dust fire to power a small refinery cracker on a jet plane?

If you've worked in petroleum industry for any length of time, you know that's not the reaction involved. You don't have a coal dust fire.

Quoting prebennorholm (Reply 33):
But the problem here is, when did we last time hear an APU actually running?

Almost every flight on every day? Ground power can't start the engine or run the air conditioners (unless it's a 787 and that's rare). A pneumatic cart can start the engine but those are rare, noisy, and maintenance and fuel hogs. If you have an air conditioning supply somewhere then you may not be running the APU for packs but you're still going to start it for engine start.

Tom.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 1:18 am

Quoting prebennorholm (Reply 33):
the APU is hardly ever used in the first place.

What's the heat haze coming out of the tail of the aircraft when at the gate then?
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 4:22 am

Quoting DocLightning (Reply 23):
The big problem is the size of sufficiently powerful electric motors. This is a submarine electric drive unit (all submarines are fundamentally electric, whatever generates the electricity), which must have a similar power output to a commercial turbofan.

You're ruining my dream.  

I think the fuel savings would cut the power required, a la the 777X.

Lightsaber
"They did not know it was impossible, so they did it!" - Mark Twain
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 4:48 am

Quoting thegeek (Reply 24):
No, most nuclear subs have direct drive

Yeah, I read that later after I'd posted while doing my own research. I stand corrected.

Quoting lightsaber (Reply 36):
I think the fuel savings would cut the power required, a la the 777X.

Yes, but a motor half the size of the one pictured here would still be way too big.

Quoting prebennorholm (Reply 33):
I have seen proposed on this thread that we generate hydrogen from jet fuel, spending the carbon on the cracking. Honestly, can we imagine a coal dust fire to power a small refinery cracker on a jet plane? Maybe? But I may be just too old to imagine that. Or maybe because I have spent my whole career in the oil business and have learned a little about refinery processes and the power they need. But in any case that would waste the energy from the carbon, subtracting further from the potential 0.75% to well below 0.5% saving.

Why can't the carbon be oxidized?

Quoting tdscanuck (Reply 29):
They also don't care about weight. A 100kW aviation electric motor is smaller than a loaf of bread (smaller than the equivalently powerful turbine, actually). 100kW is a long way from what you need for primary propulsion, but the point is that all motors are no created equal.

OK, so how big is a 100MW motor? That's more along the size of the motor you need to power an aircraft. And how big is the associated gearbox, or is one not needed?
-Doc Lightning-

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thegeek
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 5:20 am

Quoting DocLightning (Reply 37):
OK, so how big is a 100MW motor? That's more along the size of the motor you need to power an aircraft. And how big is the associated gearbox, or is one not needed?

I'd have thought it depended more on the torque than the power.
 
gigneil
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 7:33 am

Quoting prebennorholm (Reply 33):
We can't save fuel on exchanging the APU with a more efficient power source when the APU is hardly ever used in the first place.

In Europe, perhaps.

In the rest of the world, where temperatures are MUCH hotter, they run them pretty frequently.

In fact, United has a massive program to cut APU usage - their number one cost reduction program in the fuel space.

NS
 
sweair
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 9:46 am

There are a lot of research about storing hydrogen i metals as batteries sort of, maybe other lighter materials will be possible with time, for short flights stored hydrogen may be possible. But my question is if a fuel cell would be more efficient than a brayton cycle for energy extraction. Brayton is more efficient than the rankine cycle that most power plants use.
 
StickShaker
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 10:47 am

Quoting prebennorholm (Reply 33):
15% ....... 90kw .......
The numbers simply don't add up in any way.
Quoting prebennorholm (Reply 33):
Save 2/3 of the 0.75%, and we have saved 0.5%.

Its actually 15% of that 0.75% which equates to a total saving of 0.1125% in fuel costs.
In Aussie language we call that "bugger-all".

Aircraft have been designed around turbofans for the last 50 years - they are very well understood. Is it really worth adding 2 completely new chemical processes which may require relocating the APU/fuel cell and all associated monitoring/safety/certification issues just to save 0.1125% in fuel costs.

Current improvements in fuel efficiency by engine OEM's accrue at the rate of around 1% per year - 8 times the improvement that Airbus is expecting from its fuel cell.

Quoting tdscanuck (Reply 34):
Almost every flight on every day? Ground power can't start the engine or run the air conditioners (unless it's a 787 and that's rare). A pneumatic cart can start the engine but those are rare, noisy, and maintenance and fuel hogs. If you have an air conditioning supply somewhere then you may not be running the APU for packs but you're still going to start it for engine start.

787's wont be rare for too much longer and we may see other OEM's adopt a similar electric architecture.
Has there been any suggestion from OEM's to expand ground power capabilities - far less constraints involved there.


Regards,
StickShaker
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 3:30 pm

Quoting prebennorholm (Reply 33):
We can't save fuel on exchanging the APU with a more efficient power source when the APU is hardly ever used in the first place.

While it is true that airlines are trying to reduce APU usage as much as possible, with a fuel cell, you could go back to using it more often, because the longer you use it, the more fuel you save. In particular, in flight, where the APU is off. You could have the fuel cell running the whole flight, powering secondary systems, taking that load off from the engines. On ground, I think ground power would still be preferable to fuel cell use.
 
tdscanuck
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 5:18 pm

Quoting sweair (Reply 40):
But my question is if a fuel cell would be more efficient than a brayton cycle for energy extraction.

Far more efficient. Fuel cells aren't thermodynamic engines so they're not limited by Carnot efficiency. There are fundamental physical reasons you can't get above about 60% on a Brayton cycle (or any other thermo cycle), even with full intercooling/regeneration, with current generation materials. A fuel cell can get over 60% without much effort or complexity on today's technology and there's no physical reason it can't get up into the 90's.

Quoting StickShaker (Reply 41):
Is it really worth adding 2 completely new chemical processes which may require relocating the APU/fuel cell and all associated monitoring/safety/certification issues just to save 0.1125% in fuel costs.

Yes. Because it's not just about fuel savings. A fuel cell is mechanically far less complex, has less dangerous failure modes, directly generates the thing you want (electricity), and can start easily at any altitude (not true of APUs at all).

Quoting StickShaker (Reply 41):
Has there been any suggestion from OEM's to expand ground power capabilities - far less constraints involved there.

Not that I've ever explicitely heard, but each new jet is more power hungry than the one before it so the number of ground power supplies, at least at major airports, has been creeping up in response.

Tom.
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 6:21 pm

Quoting thegeek (Reply 32):
Might I suggest that putting it where the centre fuel tank is would rob some fuel tankage?

What you'd lose in tank space you'd gain by not having the pipes and hoses required to transport fuel around the plane to the cell.

My understanding is that a fuel cell does not weigh much or take up much space compared to other energy sources.

Plus, correct me someone if I'm wrong, but tank space is not the typical limiter of airplane range and performance. How often does an A320 go out with its tanks filled to maximum capacity anyway?

Quoting tdscanuck (Reply 31):
Ooooh, good point. Hadn't thought of that. Fuel cells are nearly silent (if you hear anything it's the pumps and fans, not the fuel cell itself). They do need a lot of air (so big intake and exhaust) but that's something you already have readily available in the wing-to-body fairing to support the ECS system.

Sounds like a good reason to put it there!
 
abba
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 8:07 pm

Quoting sweair (Reply 40):
There are a lot of research about storing hydrogen i metals as batteries sort of, maybe other lighter materials will be possible with time, for short flights stored hydrogen may be possible. But my question is if a fuel cell would be more efficient than a brayton cycle for energy extraction. Brayton is more efficient than the rankine cycle that most power plants use.



Many present fuel cells run at about 700-800C. They crack the fuel themselves and use the carbon to keep their operating temperature up. So it is actually - as Tom has stated - surprisingly simple. One of the advantages of fuel cells is that they are very flexible when it comes to type of fuel. Most commonly used gasses and liquids can be used.

I wonder if there are other advantages for the fuel cell not considered so far - save from being simpler and therefore easier to maintain. Is it also cheaper to produce? Is it lighter?

[Edited 2012-08-10 13:30:57]
 
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Aesma
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Fri Aug 10, 2012 11:07 pm

Quoting gigneil (Reply 14):
It comes from places far easier to obtain than jet fuel

Yes and no. Hydrogen gas is abundant in the universe, but not on Earth, because it has a tendency to bind with other stuff, like oxygen to form water. Getting hydrogen from water is trivial, but that consumes a lot of energy, so not really useful in that case.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
thegeek
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Sat Aug 11, 2012 12:56 am

Quoting abba (Reply 45):
Is it lighter?

I think that's the most important area we haven't yet been. The critics are ignoring the weight saving from going with this technology. That will translate to its own fuel saving.

Quoting D L X (Reply 44):
Plus, correct me someone if I'm wrong, but tank space is not the typical limiter of airplane range and performance. How often does an A320 go out with its tanks filled to maximum capacity anyway?

It limits some planes e.g. 77W, 77L A333. Easily fixed in the latter case. Other planes have tanks in the hold e.g. 744ER, A345 which limits revenue cargo.

I think the 737NG is somewhat limited on tankage too. Open to correction.

-
Running the APU at take off would affect the N2 and therefore the maximum thrust achieved wouldn't it?
 
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RE: Airbus To Start Testing Fuel Cells In A320 (2015)

Sat Aug 11, 2012 1:09 am

Quoting thegeek (Reply 38):
I'd have thought it depended more on the torque than the power.

You need both. Torque starts the fan blowing and power keeps it blowing. But electric motors are usually very good for torque.

Quoting sweair (Reply 40):
There are a lot of research about storing hydrogen i metals as batteries sort of, maybe other lighter materials will be possible with time, for short flights stored hydrogen may be possible. But my question is if a fuel cell would be more efficient than a brayton cycle for energy extraction. Brayton is more efficient than the rankine cycle that most power plants use.

You have two separate issues with hydrogen. The first is energy-per-mass. Hydrogen has the highest energy-per-mass of any fuel. The second is energy-per-volume. Hydrogen has about 1/5 the energy-per-volume of hydrocarbosn (IIRC). So it would be a fantastic fuel for airships (where mass is important but volume is less so) and a poor fuel for heavier-than-air aircraft where volume is at least as important as mass.

As for storage, there is cryogenic storage (tanks), which are heavy, have difficulty with filling (the hydrogen wants to boil off and needs all sorts of pressure couplings and such), and need pressure regulators for distribution. (Hydrogen is also explosive, but then again, so is Jet-A). Then there are metal hydrides, but these require high temperatures to release the hydrogen and one always wants to be careful about heating an already explosive fuel to high temperatures. It's all fun and games until a bit of oxygen leaks in. They also require huge pressures to recharge, and the metal stays behind, meaning that the weight drop as the H2 is burned is not very good.

I doubt that H2 will ever be a practical aviation fuel for airliners of the sort we currently use. I honestly think that we'll see on-board D-T pulsed fusion reactors with direct electricy conversion first (and that's a good 100 years off at least).
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