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Airbus To Start Testing Fuel Cells In A320 (2015)  
User currently offlineBralo20 From Belgium, joined May 2008, 628 posts, RR: 0
Posted (2 years 3 months 2 weeks 3 days ago) and read 12094 times:

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)

48 replies: All unread, showing first 25:
 
User currently offlineAquila3 From Italy, joined Nov 2010, 308 posts, RR: 0
Reply 1, posted (2 years 3 months 2 weeks 2 days 23 hours ago) and read 11909 times:

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.



chi vola vale chi vale vola chi non vola è un vile
User currently offlinejox From Sweden, joined Jan 2003, 126 posts, RR: 0
Reply 2, posted (2 years 3 months 2 weeks 2 days 23 hours ago) and read 11791 times:
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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?

User currently offlineStickShaker From Australia, joined Sep 2004, 758 posts, RR: 5
Reply 3, posted (2 years 3 months 2 weeks 2 days 22 hours ago) and read 11706 times:

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]

User currently offliner2rho From Germany, joined Feb 2007, 2736 posts, RR: 1
Reply 4, posted (2 years 3 months 2 weeks 2 days 21 hours ago) and read 11427 times:

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.


User currently offlinemasi1157 From Germany, joined Feb 2011, 124 posts, RR: 0
Reply 5, posted (2 years 3 months 2 weeks 2 days 21 hours ago) and read 11400 times:

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

Yes.


Gruß, masi1157


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 6, posted (2 years 3 months 2 weeks 2 days 19 hours ago) and read 11102 times:

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.


User currently offlineStickShaker From Australia, joined Sep 2004, 758 posts, RR: 5
Reply 7, posted (2 years 3 months 2 weeks 2 days 19 hours ago) and read 10992 times:

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


User currently offlinespink From United States of America, joined Aug 2005, 318 posts, RR: 1
Reply 8, posted (2 years 3 months 2 weeks 2 days 14 hours ago) and read 10588 times:

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.


User currently offlineDocLightning From United States of America, joined Nov 2005, 20191 posts, RR: 59
Reply 9, posted (2 years 3 months 2 weeks 2 days 12 hours ago) and read 9658 times:

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.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 10, posted (2 years 3 months 2 weeks 2 days 12 hours ago) and read 9613 times:

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.


User currently offlineabba From Denmark, joined Jun 2005, 1376 posts, RR: 2
Reply 11, posted (2 years 3 months 2 weeks 2 days 12 hours ago) and read 9589 times:

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?


User currently offlinegigneil From United States of America, joined Nov 2002, 16347 posts, RR: 85
Reply 12, posted (2 years 3 months 2 weeks 2 days 12 hours ago) and read 9547 times:

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


User currently offlineDocLightning From United States of America, joined Nov 2005, 20191 posts, RR: 59
Reply 13, posted (2 years 3 months 2 weeks 2 days 11 hours ago) and read 8905 times:

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.


User currently offlinegigneil From United States of America, joined Nov 2002, 16347 posts, RR: 85
Reply 14, posted (2 years 3 months 2 weeks 2 days 8 hours ago) and read 7709 times:

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


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 15, posted (2 years 3 months 2 weeks 2 days 6 hours ago) and read 7285 times:

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.


User currently offlineStickShaker From Australia, joined Sep 2004, 758 posts, RR: 5
Reply 16, posted (2 years 3 months 2 weeks 2 days 6 hours ago) and read 7243 times:

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]

User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3424 posts, RR: 4
Reply 17, posted (2 years 3 months 2 weeks 2 days 5 hours ago) and read 7060 times:

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.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 18, posted (2 years 3 months 2 weeks 2 days 5 hours ago) and read 7010 times:

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.


User currently offlinelightsaber From United States of America, joined Jan 2005, 13422 posts, RR: 100
Reply 19, posted (2 years 3 months 2 weeks 2 days 5 hours ago) and read 6977 times:
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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.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlinethegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 20, posted (2 years 3 months 2 weeks 2 days 5 hours ago) and read 6915 times:

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.


User currently offlineStickShaker From Australia, joined Sep 2004, 758 posts, RR: 5
Reply 21, posted (2 years 3 months 2 weeks 2 days 4 hours ago) and read 6757 times:

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


User currently offlinethegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 22, posted (2 years 3 months 2 weeks 2 days 4 hours ago) and read 6603 times:

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.


User currently offlineDocLightning From United States of America, joined Nov 2005, 20191 posts, RR: 59
Reply 23, posted (2 years 3 months 2 weeks 2 days 3 hours ago) and read 6399 times:

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


User currently offlinethegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 24, posted (2 years 3 months 2 weeks 2 days 2 hours ago) and read 6279 times:

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.


25 spink : 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/therm
26 sweair : 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 fr
27 StickShaker : 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
28 Post contains links abba : 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/
29 tdscanuck : Why would you add another pipe? Use the one that's already there...no extra weight, no extra maintenance, no new hazard. The weight of the fuel isn't
30 D L X : 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 compone
31 tdscanuck : 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). The
32 thegeek : Right. Not sure how I forgot that. Might I suggest that putting it where the centre fuel tank is would rob some fuel tankage? Perhaps you could put i
33 prebennorholm : 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
34 tdscanuck : 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. Almost eve
35 thegeek : What's the heat haze coming out of the tail of the aircraft when at the gate then?
36 Post contains images lightsaber : You're ruining my dream. I think the fuel savings would cut the power required, a la the 777X. Lightsaber
37 DocLightning : Yeah, I read that later after I'd posted while doing my own research. I stand corrected. Yes, but a motor half the size of the one pictured here woul
38 thegeek : I'd have thought it depended more on the torque than the power.
39 gigneil : 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 prog
40 sweair : 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
41 StickShaker : 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
42 r2rho : 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, becaus
43 tdscanuck : Far more efficient. Fuel cells aren't thermodynamic engines so they're not limited by Carnot efficiency. There are fundamental physical reasons you c
44 D L X : 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
45 abba : 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 act
46 Aesma : 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
47 thegeek : 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 tra
48 DocLightning : You need both. Torque starts the fan blowing and power keeps it blowing. But electric motors are usually very good for torque. You have two separate
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