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White Paper: AIP

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Contributor:	Ray Keefer

Last update:	11/17/97

Synopsis:	This page contains research on AIP (Air Independent 
		Propulsion). This is a propulsion method based on an air
		breathing engine that is fed oxygen as needed while submerged.
	  	This research was done in respose to some mail on the
		listserver group.


Disclaimer:	You are resposible for your own safety. Even though
		this information may work or seem resonable in some 
		cases you need to approach the subject carefully and 
		even aquire the help of a Marine Architect before applying
		into one of your designs.

Body:

>Well, no, actually, some of the diesel-electric systems I've heard about
>are "closed-loop" systems that (like a rebreather) can allow an engine to
>"breathe" with no external air supply or exhaust. I believe the British
>navy has perfected such a system. They recycle the exhaust, chemically
>remove all the bad stuff, and reinject it into the engine with a small,
>fresh supply bleeding in from storage tanks.
>

AIP (Air Independant Propulsion). The Germans, Norwegions or Swedes are
working on it. Actually they have operational boats in service. The
air flask is a hugh helix coil around the pressure hull (either
inside or outside, I don't know which) along most of the length.
Endurance is a couple of weeks if I remember right. 

Looking at my references, on Page 26 of "Engineers at Work: Attack
Submarine" by Ian Graham, Gloucester Press, Aladdin Books Ltd., 1989,
ISBN 0 86313 970 1:

	The "Maritalia" midget submarine is propelled by an "anaerobic"
	diesel engine. Oxygen needed for burning the diesel fuel
	is stored inside the "toroidal" (coiled-pipe) hull. Exhaust gases
	are also stored in the submarine, since pumping them into the sea
	would allow detection by an enemy. This submarine can travel under
	water for great distances using its diesel-powered electric motor,
	which a normal diesel craft cannot do.

The picture looks much like a minature LA Attack sub.

On page 288 of "Submarine: A Guided Tour Inside a Nuclear 
Warship" by Tom Clancy, Berkeley Books, 1993, ISBN 0-425-13873-9:

	Sweden

	Of all the nations that operate submarines, none is probably less
	understood and more underestimated than Sweden. The Swedes have 
	always had an independaent streak when it comes to defense issues, 
	and this is certainly true of their submarine force. At the moment. 
	They produce some of the most advanced conventionally powered 
	submarines n the world. Their boats have a decidedly inshore design
	philosophy, consistent with the Swedish requirements of operating 
	in the Baltic. In addition, the Swedes are leaders in 
	non-nuclear Air Independent Propulsion  (AIP) systems. Currently 
	they are finishing development of the Gotland (A-19 class) boats, 
	equipped with a Steriling AIP system to keep the batteries charged 
	for longer submerged endurance. Like all other nations, the Swedes 
	are aggressively marketing their boats for export. They have had a 
	particular success with the sale of six boats (the Collins class) 
	to Australia.

It then goes on with specs. On page 292, Clancy talks about the German
Type 212 class:
	
	Their newest boats, the Type 212s, are capable of being equipped
	with a liquid oxygen/hydrogen fuel cell AIP system.

On pages 128-130 of "Concepts in Submarine Design" by Ray Burcher and  
Louis Rydill, Cambridge University Press, 1995, ISBN 0 521 55926 X,
in part:

	One solution to the submerged problem would be to carry not only
	the comustible fuel but also the oxygenation agent on the submarine,
	i.e. carry oxygen in some form which may either be as liquid oxygen
	or as a highly oxygenated fluid of which high test peroxide is a 
	well known form.

It goes on  to talk about Sweden and their use of the Stirling Cycle
with a reciprocating engine. Then Re-cycle Diesel Engine [refed exhaust
back to engine with added oxygen and fuel as needed]. Then on to fuel
cells. So far no submarine is using fuel cells since the World's Navies
tend to be conservative with their designs of multi-million dollar subs.

>>         And yeah, there's not a hydrogen filling station on every corner.
>> Yet.  But
>> for our use here with personal subs, I'm sure that could be overcome.  I 
mean
>> if you're building a submarine from scratch [and you'll need a lot of
>> scratch ],
>> you're going to have to build some support equipment on 
your own, too.
>
>It's not hard to make hydrogen (its a by-product of electrolysis), but you
>do need an external electricity supply. So, you have a big tank at home and
>a system for generating H. You do a transfer to your sub's tank(s) in the
>morning, and turn the system on when you leave. While you're off having
>fun, the system is slowing turning water into hydrogen and oxygen, and you
>capture both (H as fuel, O2 for the rebreather).
>

How do you compress the hydrogen? Do you store in compressed or do you
liquidfy it? You get more storage in liquid state but the hydrogen also
get VERY cold. 

Another thing to watch is that hydrogen is oderless and very flamable.
You have to design your system so that hydrogen areas are vented well.

>The really nice thing about fuel cells is that if you could refill your
>tanks from shore in a matter of minutes, instead of waiting for 12 hours to
>recharge your batteries.

Another nice thing is that you get fresh drinking water from the 
combination of hydrogen and oxygen. One of the reasons NASA likes them.

>
>But, of course, for really small subs, the critical thing is power output
>compared to volume. If it's better than batteries, you'd have it made. If
>not, well, you're out of luck. From the limited amount of research I've
>done, I'm inclined to believe that batteries are more effecient per unit
>volume, but then again maybe someone knows otherwise...
>

I don't know. In "Concepts in Submarine Design" the authors alluded to 
the fact that fuel cells are very scalible. Just not a proven to be
reliable source in submarines. They don't mention power density.