Alternative sub propulsion tech?

barney41

Member
Something interesting. It's ability to extract oxygen from water and store it in crystalline form could lead to an alternative to nuke reactors or currient AIP systems on subs one day.


Weird Crystal Can Absorb All The Oxygen In A Room -- And Then Release It Later | Popular Science
Weird Crystal Can Absorb All The Oxygen In A Room -- And Then Release It Later

Researchers from the University of Southern Denmark say they’ve invented a crystal that pulls oxygen out of the air and even water. Apparently, just a spoonful of the stuff can suck up all the oxygen in a room.

More at the link.
 

My2Cents

Active Member
For a large spoon or a small room.

This does offer some interesting possibilities. Heat it to 140°C (285°F) to release the oxygen, then just flow air through it to recharge. A major improvement over the limited capacity LOX based systems. Bulkier and heavier for a given capacity, but the easy rechargability could make it a winner if able to snorkle as needed.
 

John Fedup

The Bunker Group
Something interesting. It's ability to extract oxygen from water and store it in crystalline form could lead to an alternative to nuke reactors or currient AIP systems on subs one day.


Weird Crystal Can Absorb All The Oxygen In A Room -- And Then Release It Later | Popular Science
Weird Crystal Can Absorb All The Oxygen In A Room -- And Then Release It Later

Researchers from the University of Southern Denmark say they’ve invented a crystal that pulls oxygen out of the air and even water. Apparently, just a spoonful of the stuff can suck up all the oxygen in a room.


More at the link.
Interesting paper. The crystal molecule is pretty complex and has a molecular weight of almost 2000. As with all things, the cost of industrial synthesis will determine what future this material might have.
 

Krogh

New Member
Dear gf0012-aust
Thanks for your reply in another thread, I'll continue it here, since it was OT and in the hope that you can shed some light on this for me.

Quote:
Originally Posted by Krogh View Post
So my question is, whats the problem? why not add in more? e.g. replace the diesel?, are the cells taking up to much space?

thanks.
I spent a number of years working with french hydrogen fuel cells, german hydrogen fuel cells and australian ceramic fuel cells. The australian tech was then and is still regarded as the best mass per energy generation combination in the world. Unfortunately it was another great australian tech that didn't get any Federal support and they ended up basing themselves in Germany

But without further digressing, there is no direct relationship in HP/KW generation terms between fuel cell variants and dry/wet/saline battery techs

its like looking at a tesla e-car accelerate against a petrol engined super car - the drivetrain on one is a 1/5th of the physical mass - but the batteries/fuel tank mass comparison swings the other way

all the long range underwater USV tech I was exposed to used electric motors and sealed batteries. the tech duration capability under set conditions improved by 800% in 3 years - so the potential was enormous

I'd add that the world has also moved on beyond just LiPo banks, in smaller platforms there has been significant testing done using LiPo and super capacitors

the amercans did significant work using super conductors and super capacitors to achieve nuke like performance.

I can't comment on the absolutes of using the tech as you propose, but I can tell you that there are no constraints to be being able to do so.

there were developments when I was involved into using salt water as part of the hydrogen conversion process for fuel cells. IOW the ocean became your fuel tank.
From what I understand of this: Fuel cells as primary energy source appears technically feasible for even a larger sub. Though, as I understand you, the "powerplant" has a limitation in that It can't deliver "surge" power (I quess a single cell has a more or less constant output, so the possible high operating output is more or less linear with number of cells?).
So to merit that, as I understand you, you'll need a secondary energy source or "bank" f.ex. batteries or something like a capacitor, to deliver needed surge or peak out put?

We could imagine the full cells will then recharge batteries in "low" periods

Not being an expert in batteries, doesn't the Li ion batteries give us exactly the needed? They can deliver high output (surge) and can be recharged quickly.
 

Todjaeger

Potstirrer
Dear gf0012-aust
Thanks for your reply in another thread, I'll continue it here, since it was OT and in the hope that you can shed some light on this for me.



From what I understand of this: Fuel cells as primary energy source appears technically feasible for even a larger sub. Though, as I understand you, the "powerplant" has a limitation in that It can't deliver "surge" power (I quess a single cell has a more or less constant output, so the possible high operating output is more or less linear with number of cells?).
So to merit that, as I understand you, you'll need a secondary energy source or "bank" f.ex. batteries or something like a capacitor, to deliver needed surge or peak out put?

We could imagine the full cells will then recharge batteries in "low" periods

Not being an expert in batteries, doesn't the Li ion batteries give us exactly the needed? They can deliver high output (surge) and can be recharged quickly.
One of the potential issues with using AIP and/or fuel cell technology is the energy density available. Right now, in most instances, the overall energy available from a gen set as well as fuel bunkerage is greater non diesel-electric systems, for the same overall displacement & volume. The energy density in diesel fuel (and other hydrocarbons) is greater than most other fuel sources. In terms of energy collection and storage systems, it looks like some might approach or even reach a comparable level, unfort we do not seem to be there quite yet.
 

Krogh

New Member
One of the potential issues with using AIP and/or fuel cell technology is the energy density available. Right now, in most instances, the overall energy available from a gen set as well as fuel bunkerage is greater non diesel-electric systems, for the same overall displacement & volume. The energy density in diesel fuel (and other hydrocarbons) is greater than most other fuel sources. In terms of energy collection and storage systems, it looks like some might approach or even reach a comparable level, unfort we do not seem to be there quite yet.
So you are saying that a primary propulsion system with Fuel cells e.g. PEM and batteries, all in all simply will take up too much space, if one both wants range and speed comparable to a DE alternative?
 

StingrayOZ

Super Moderator
Staff member
Pound for pound diesels are going to win. Diesel is actually a pretty dense fuel source, diesel engines are fairly compact. Which is why for ships of all types where plentiful air is available no one really considers anything else, even nuclear power is more of an aberration, really only effective in a few large carriers where it frees up space for jet fuel.

Fuel cells can be used in a larger sub. But the question has to be raised why is the sub larger. Larger items are often used differently to smaller ones. Fuel cells work well in a limited environment. You want to be going slow, you want to have effectively no indiscretion events.

http://www.bmtdsl.co.uk/media/10576...r-and-Propulsion-Conpaper-Pacific08-Jan08.pdf (this is not a definitive paper and much of the data is "estimated" and flawed, but is illustrative).
You can see in the table of the type 214 that high speed AIP is effectively wasted not, really adding much capability. But as you get to <8kts, particularly <4kts you have a significant improvement in endurance. You can see that for subs who CONOPs is a very slow patrol, this can offer near nuclear like endurance. You dive, you crawl along at 4kts, you surface you go home. In this case AIP's oneshot capability works fine. Nations have doctrine and CONOPs that results in platforms evolved to take use of this capability. Japanese subs for example, are extremely strong and very deep diving, it would seem that is inline with their CONOPs.

AIP however doesn't help in more blue water environments, where you want to sustain long transits, or higher speed patrols. In these cases your better usually in developing subs with more diesel engines and bigger batteries, that can maintain a high transit speed and low indiscretion rate for very long period (the entire time at sea).

Larger subs like Collins, often have more power hungry systems than smaller subs. Larger more powerful sensors, more advanced and capable combat systems, often related or borrowed from nuclear submarines which in comparison have nearly limitless energy capacity. These type of systems would make quick work of the potential endurance advantage of any AIP system. With Collins there really hasn't been a need to install the AIP sterling engines (which we have) as they don't fit the CONOPs or the doctrine of the RAN. Apparently the RAN doesn't use subs in the same manner as many European and some Asian navies, or not enough to justify AIP.

Getting back to fuel cells. Fuel cells can be very efficient, but storing hydrogen is very problematic and often lacks density in a workable application. Storing oxygen is slightly less problematic, but still brings up a range of difficulties. All that space could be put to batteries or even better, lithium ion batteries, which are not just lower maintenance and simpler than fuel cells, they are rechargeable at sea (and as such can boost transit performance), require less maintenance in port and at sea, and can provide large amounts of energy quickly (propulsion, sensors, systems etc) and do so in a way much more efficient than lead acid and far more practical than fuel cells.

IMO AIP fuel cells/stirling cycles has peaked and is now in decline. The future isn't fuel cells, its more advanced battery chemistry in the form of lithium batteries (which were really a recent invention and recent commercialization). Japan has already ditched its 1980's stirling cycle AIP for lithium batteries. Others will follow in future designed subs fairly quickly, as the technology is low overhead and easy to implement (unlike fuel cell AIP which requires special tanks, systems, designed support etc).
 

gf0012-aust

Grumpy Old Man
Staff member
Verified Defense Pro
IMO AIP fuel cells/stirling cycles has peaked and is now in decline. The future isn't fuel cells, its more advanced battery chemistry in the form of lithium batteries (which were really a recent invention and recent commercialization). Japan has already ditched its 1980's stirling cycle AIP for lithium batteries.
plus one. Have said before that AIP is not a panacea for persistence in contemp terms.

Any consideration to install should factor in how it will be replaced at the MLU stage.

if however anyone wants nuke performance, then no hybrid solution will provide that.

there are also shifts underway to superconductors and super capacitors, they are a far better solution to dealing with surge events assuming that your generators have the time to reload them. A number of small energy hungry combat and control systems are looking at capacitors coupled with efficient energy generators
 

Krogh

New Member
Pound for pound diesels are going to win. Diesel is actually a pretty dense fuel source, diesel engines are fairly compact. Which is why for ships of all types where plentiful air is available no one really considers anything else, even nuclear power is more of an aberration, really only effective in a few large carriers where it frees up space for jet fuel.

Fuel cells can be used in a larger sub. But the question has to be raised why is the sub larger. Larger items are often used differently to smaller ones. Fuel cells work well in a limited environment. You want to be going slow, you want to have effectively no indiscretion events.

(this is not a definitive paper and much of the data is "estimated" and flawed, but is illustrative).
You can see in the table of the type 214 that high speed AIP is effectively wasted not, really adding much capability. But as you get to <8kts, particularly <4kts you have a significant improvement in endurance. You can see that for subs who CONOPs is a very slow patrol, this can offer near nuclear like endurance. You dive, you crawl along at 4kts, you surface you go home. In this case AIP's oneshot capability works fine. Nations have doctrine and CONOPs that results in platforms evolved to take use of this capability. Japanese subs for example, are extremely strong and very deep diving, it would seem that is inline with their CONOPs.

AIP however doesn't help in more blue water environments, where you want to sustain long transits, or higher speed patrols. In these cases your better usually in developing subs with more diesel engines and bigger batteries, that can maintain a high transit speed and low indiscretion rate for very long period (the entire time at sea).

Larger subs like Collins, often have more power hungry systems than smaller subs. Larger more powerful sensors, more advanced and capable combat systems, often related or borrowed from nuclear submarines which in comparison have nearly limitless energy capacity. These type of systems would make quick work of the potential endurance advantage of any AIP system. With Collins there really hasn't been a need to install the AIP sterling engines (which we have) as they don't fit the CONOPs or the doctrine of the RAN. Apparently the RAN doesn't use subs in the same manner as many European and some Asian navies, or not enough to justify AIP.

Getting back to fuel cells. Fuel cells can be very efficient, but storing hydrogen is very problematic and often lacks density in a workable application. Storing oxygen is slightly less problematic, but still brings up a range of difficulties. All that space could be put to batteries or even better, lithium ion batteries, which are not just lower maintenance and simpler than fuel cells, they are rechargeable at sea (and as such can boost transit performance), require less maintenance in port and at sea, and can provide large amounts of energy quickly (propulsion, sensors, systems etc) and do so in a way much more efficient than lead acid and far more practical than fuel cells.

IMO AIP fuel cells/stirling cycles has peaked and is now in decline. The future isn't fuel cells, its more advanced battery chemistry in the form of lithium batteries (which were really a recent invention and recent commercialization). Japan has already ditched its 1980's stirling cycle AIP for lithium batteries. Others will follow in future designed subs fairly quickly, as the technology is low overhead and easy to implement (unlike fuel cell AIP which requires special tanks, systems, designed support etc).
Thanks for the reply and thanks a lot for the link.

From what I gather from the link - and let's accept the estimates, if not for anything else, then because it's the best we/(I) got.



In "Patrol".
The data in the link demonstrates that the AIP systems of the german U214 or the Swedish Gotland provide these boats with an order of magnitude on endurance at quite high speeds (for the german boat all ready at 9knts).
In comparison, they significantly (about an order of magnitude) outperform the other boats, running on batteries, on this parameter.

According to the data:
At 8 knots, e.g. a Collins running on batts have 11h while an U214 running on batts and AIP has 400h.
At 4 knots a Collins has 100h (some 4 days) on batts while U214 on batts and AIP has 1500h (60 days).

To my knowledge, there are no known battery improvements in the "R&D pipeline" any where in the world, that can come close to fill such a gap.

At the same time the data also show that these AIPs+Batts are not enough to supply the energy needed for "transit" or in short sustained "high speeds". And there is no existing alternative to Diesel, on this parameter. So, I quess we are back to the diesel hybrids of that reason.



"IMO AIP fuel cells/stirling cycles has peaked and is now in decline."
Perhaps, though Fuel cells and there are many types, are, to my knowledge, "theoretically" superior to combustion engines on many parameters and are the subject of intense research and development. E.g. they are more efficient, don't polute (so much) and mechanically far more simple. the fuel cell typically has a higher energy output per mass or volume than diesel (though fuel storage might be a problem) And certainly, one attribute should be of interest in military applications: vibrationless.

It appears to me that while siemens has AIP fuel cell working, with it's limitations, little work appears to be done in the field of a Fuel Cell system that can replace the diesel engines in a sub all together and doesn't have to be air independent, because that opens up for some other cell types (also that doesn't work on hydrogen and other explosives:eek: ) I find that surprising.


"Japan has already ditched its 1980's stirling cycle AIP for lithium batteries"

I was under the impression that these japanese Soruyu, use Kockum's Stirlings?
Though I wouldn't bet on Stirlings, fantastic, but difficult engine, and the industrial infrastructure behind them is weak. As far as I know small stirlings are only used for military and Stirlings are else used only in large powerplants, so you will be one of few to pay for continued maintenance and development of a difficult machine....

What's your view on the Li-ion batts, they have the unfortunate property that the internal resistance increase as you recharge (that's why your cell phone operates shorter and shorter) is that of no practical consequvence for a sub? (just buy some new?)
 

StingrayOZ

Super Moderator
Staff member
Those figure certainly aren't true and accurate but are just estimates, so we can only really talk in vague terms about them.

AIP has its moments going slow. AFAIK no one is underwater for 60 days using AIP. Its usually more like 21 days as claimed by manufacturers, even at slow speeds. Then there are questions. At what temperature? Tropical waters? Arctic waters? At maximum depth? How reliable? Are there limitations that will affect operations?

To my knowledge, there are no known battery improvements in the "R&D pipeline" any where in the world, that can come close to fill such a gap.
It doesn't have to, it gets back to CONOPs. I would think it would be rare even for SSN's to remain completely submerged at depth for 60 days.

Lithium batteries aren't just about increasing storage density. Lithium key advantage over lead acid is really when you want to put a lot of current in and take a lot of current out. Combined with supercapacitors, you can surge huge amounts of energy (in or out) without the penalty of lead acid. Lithium potentially makes your indiscretion more effective. You can charge quicker, have less issues from your batteries. While fuel cell AIP is quiet, lithium ion is even quieter. Fuel cell AIP supplies small amounts of power, lithium solutions can surge significantly more.

Both the French and German proposals see lithium as adding to the party rather than replacing fuel cells. The Japanese did replace a rather dated (hence my 1980's or should that be 1880's) Kockums sourced Stirling AIP system directly with lithium ion, so it could potentially make that difference, even for very deep diving subs like the Japanese. For them, its worth it.

I don't see diesel engines disappearing completely in the near/medium term. Its about complimenting them. Making them more efficient and capable. Diesel engines are cheap to buy and operate, diesel is cheap and is a dense energy source. Even nuclear submarines have diesel engines as backups. Nuclear submarines still have periscopes, they still approach the surface for a large number of reasons.

I think AIP systems will still be a part of submarines for a while yet, but I think subs will be less and less designed around them. Everyone wants to get away from carrying hydrogen which is stored at low density and is generally problematic. Ideally you could make your own hydrogen from diesel fuel using a reformer, but making enough efficiently with regular diesel is space consuming. Liquid oxygen needs to be kept cool obviously. Long transits through tropical water do not seem like ideal situations for any AIP that uses liquid oxygen.

For many navies, AIP doesn't really deliver for the CONOPs. Japan has pretty extensive fuel cell capabilities, with Toyota, Honda and other manufacturing fuel cell cars, industrial equipment etc so its not like the technology is beyond them. But they have migrated directly to lithium ion as the replacement for its AIP.

The latest MESMA system is alleged to power at sub at 6kts while having excess available for charging batteries (or allowing greater than 6kt performance), and can reform fuel from diesel. TKMS is also looking at reforming from methanol, the spanish do reform from Methanol.

TKMS has proposed a system to replenish liquid oxygen at sea, allowing it to be replenished during snorting.

So in design terms, I think it would be worth while allocating space/weight for AIP, and some sort of liquid oxygen storage. AIP is likely to become more compact over all. Enhancing capabilities rather than being the magical do everything power source of the future.

Lithium ion in subs is likely to be part of a wide system. GF who is much more aware and informed than I, indicates supercapacitors are part of that solution, further amplifying their strengths. I think between them they can offer huge benefits in many applications. They would be paired with a complex battery management system to squeeze the most out of the different types of energy systems on a sub.

Which is then the key part, trying to integrate and make the most of the technologies now available.
 

Krogh

New Member
Stingray
Thanks for the reply.

I agree with the advantages of Li-ion batts.

It will be interesting to see the future developments, in my mind diesels appears to be an "innovation salient", something that could be the target of innovation.

I would think that Conops are hardly independent of the technical attributes of the platform in question and that tech isn't independent of conops either...
 

gf0012-aust

Grumpy Old Man
Staff member
Verified Defense Pro
I would think that Conops are hardly independent of the technical attributes of the platform in question and that tech isn't independent of conops either...
CONOPs covers things like constraints, tempo and to some extent whats needed to establish a battle rhythm in certain scenario.

CONOPS in and of itself is not the defining tool to design, develop, plan etc....
 
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