AFAIK currently the following AIP systems are being used:
* Closed cycle steam turbines (MESMA; e.g. Scorpene)
* Fuel cell (e.g type 212, 214)
* Stirling cycle (Gotland class)
Fuel cell is considered to be the most quiet one, however interestingly Sweden has recently decided to build the A-26 sub, and that this will have the Stirling AIP:
http://www.kockums.se/en/products-services/submarines-systems/littoral-submarines/project-a26/
It is also interesting to note that the Japanese Sōryū (SS16) class is being built with the Stirling AIP — So although the fuel cells are probably more quiet than Stirling, perhaps the Stirling is “sufficiently quiet”?
On the other hand, the Spanish S-80 seems to use a “new” type of fuel cells, that run on Ethanol and Oxygen instead of Hydrogen and Oxygen:
To me Hydrogen seems very difficult to deal with and I am in a way surprised that the Germans went for Hydrogen fuel cells; but since they did I guess it has some advantages compared to the Ethanol fuel cells? Or was the Ethanol fuel cell technology not available when the Germans designed their fuel cell AIP system?
So, what are the pros and cons of these systems? Any thoughts from the experts?
By: Loke - 21st May 2010 at 14:13
– But not only AIP is important: When a submarine used to snort to recharge the battery it also refreshed the air on board. Now the snorting has been solved (partly) the next bottleneck is the air quality. CO2-scrubbers as used on nuclear subs are large and are consuming a lot of electricity, not suitable for an board AIP-submarine. The air quality is that much of an issue that in practice an AIP equipped submarine will still be snorting every 2 days or so to refresh the air. So not only AIP has to improve but also other systems iot make the AIP-submarine successful.
The Swedish Navy has operated submarines equipped with air independent propulsion for two
decades. This type of submarine can stay submerged for periods far longer than other nonnuclear
submarines are capable of. The air quality during longer periods of submersion has so far
not been thoroughly investigated. This study presents results for a number of air quality
parameters obtained during more than one week of continuous submerged operation. The
measured parameters are pressure, temperature, relative humidity, oxygen, carbon dioxide,
hydrogen, formaldehyde and other volatile organic compounds, ozone, nitrogen dioxide,
particulate matter and microbiological contaminants. The measurements of airborne particles
demonstrate that air pollutants typically occur at a low baseline level due to high air exchange
rates and efficient air-cleaning devices. However, short-lived peaks with comparatively high
concentrations occur, several of the sources for these have been identified. The concentrations of
the pollutants measured in this study do not indicate a build-up of hazardous compounds during
eight days of submersion. It is reasonable to assume that a substantial build-up of the
investigated contaminants is not likely if the submersion period is prolonged several times, which
is the case for modern submarines equipped with air independent propulsion.
Seems the Swedes can handle an 8-day submerged mission — and it seems to me that 8 days is not the maximum…
By: radar - 10th May 2010 at 17:49
That’s why the Germans are building a hydrogen refuelling ship for use in overseas ports iot refuel subs in between patrols. But mind you: refuelling of the AIP system costs 200.000 euro and that is quite expensive for a general peace time patrol.
source for these two points? from my understand it’s planed to use containerized refueling systems and no dedicated ship.
By: StevoJH - 10th May 2010 at 10:06
In 2009 worldwide ethanol production was 74 billion litres. How much would a sub use a year? I agree farmland is an issue — but that would not be because of a few subs, but rather because of an increasing number of cars (already in the millions) running on ethanol.[/QUOTE]
Depends on how you charge them though, if you produce hydrogen during times when there is an excess of electricity running around the wires its basically free.
By: Loke - 10th May 2010 at 08:32
According to Wikipedia 100% Brazilian bioethanol is priced at 3.88 UDS a gallon; is Hydrogen really much cheaper than that? Some sources says Hydrogen cost 84 USD “per gallon of gasoline equivalent” http://www.recoverybydiscovery.com/hydrogen.htm which to me seems more expensive and not cheaper than ethanol…
In 2009 worldwide ethanol production was 74 billion litres. How much would a sub use a year? I agree farmland is an issue — but that would not be because of a few subs, but rather because of an increasing number of cars (already in the millions) running on ethanol.
By: Bager1968 - 10th May 2010 at 06:39
No… the hydrogen is produced on land (at least for current subs)… it is just that ethanol requires far more (and more expensive) production/preparation facilities… including either significant amounts of farmland to produce the plant sugars needed to ferment into the ethanol, or a large supply of petroleum to be refined, as ethanol intended for industrial use is also produced from by-products of petroleum refining. equipment, etc.
Hydrogen can be produced in a relatively small plant that uses a river as its materials source.
Economics is a major difference… as well as the resource base. Farmland set aside for ethanol production is not available for food production, and we all know about the economic/political problems with petroleum (oil).
By: Loke - 9th May 2010 at 13:32
Are you saying that the German subs are producing Hydrogen during their mission? I thought it was generated on land and stored on the sub?
By: StevoJH - 9th May 2010 at 13:06
For starters you can’t produce ethanol by running a current through water.
The thing that must be remembered with AIP submarines is that they don’t really increase the mobility of the submarine, they just increase the amount of time it can be submerged.
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May 9, 2010 at 10:59 am