February 28, 2017

German, French, Spanish, Reformer Fuel Cell AIP, Japanese LIBs

Advanced French AIP proposal. “Simplified” Layout of Diesel Fuel Processing Equipment (Diesel Fuel Autothempermal Reformer – SOFC). Layout and description courtesy Bakst Engineering.


The following is the section on AIP within an excellent article The Driving Factor In The SEA 1000 Choice The Submarine Propulsion Chain by submarine expert Rex Patrick, from Sydney, Australia. This was on pages 40 to 44 of the October 2015 issue (Volume 41, Number 8) of the Asia-Pacific Defence Reporter (APDR). APDR is an excellent magazine provided by subscription.

It was written before the Australian Government’s 26 April 2016 SEA 1000 decision in favour of the French DCNS Shortfin – but the article's comments on AIP still appear accurate.

Significantly the article is also published on the Siemens' website here

Pete has bolded for emphasis some words in the following AIP section and also added footnotes [1] and [2]. The footnotes indicate that the AIP section is still current and accurate. Japan and Lithium-ion Batteries (LIBs) are also discussed towards the end.



The primary purpose of an AIP system is to convert stored reactant energy into electrical energy for the submarine’s main battery and to do so independently of the surface atmosphere. It provides little benefit during transits but is invaluable when operating slowly within an operational area.

TKMS will almost certainly offer Australia a reformer/ FC solution. Being a large submarine, it will demand two reformers and four 120 kW FCs.

The first element of TKMS’ AIP solution is a Methanol reformer that extracts hydrogen from methanol and feeds it directly into the FC. Methanol is selected because of its worldwide availability, high hydrogen content, low reforming temperature (250°C), reformation ease and high reforming efficiency (80 to 90%). LOX is also used in the reforming process. Sub-system waste is pressurised CO2 which can be discharged to sea down to full diving depth. The reformer is packaged in an enclosure with its own special ventilation system for cooling.

Each reformer is capable of producing enough hydrogen to supply two fully loaded 120 kW cells. It removes the need to store hydrogen on board, which is problematic from a supply availability and refuelling complexity perspective, and is also difficult on 2000+ tonne submarines because of the weight of the hydrogen’s metal hydride storage bottles.

The reformer has a two to three hour start-up time. Operationally, the idea is to start it up in the patrol area in block periods where AIP can be exploited, potentially for weeks on end, dependant on the amount of reactant stored on board.

The reformer has been in development since 1995 and a test site has been in operation for a decade, with FCs connected to it since 2010. A reformer suitably packaged for installation on board submarines is currently undergoing set-to-work in Kiel. Whilst the reformer has not been fielded on a submarine yet it is at the test bed state and therefore it attracts a low SEA 1000 project risk label.

Moving to the FC, TKMS will offer the second generation Siemens 120 kW Polymer Electrolytic Membrane (PEM) FC. The PEM FC works by feeding standard industry-grade LOX and high purity hydrogen into the cell which generate electricity in response. It does this silently and at a low temperature (80°C). It is different to a battery in that it stores no charge; it simply generates electrical energy so long as the reactants are fed into the cell. The cell is extremely (fuel burn) efficient at between 50 and 70%. Its ‘waste’ outputs are potable water, which is fed into holding tanks, and (1%) oxygen, which is fed into the submarine’s atmosphere to assist in maintaining breathable air during prolonged AIP dived periods.

The FC has been under development by Siemens since the early eighties. It was first trialled on a German Type 205 test submarine in 1988 and then contracted for supply into the German and Italian Type 212 program. The first production FC went to sea in 2002 and it is now a very mature system at sea on 24 submarines, meaning it is a minimal project risk component of the German SEA 1000 solution.

The reformer/FC system meets all of the fundamental requirements of an AIP system; high efficiency, silent, low magnetic signature, light and compact, generates no pollution or heat, reliable, relatively easy to maintain and requiring no additional operating personnel.

It is interesting that the German Defence Department funded TKMS starting in 2007 to conduct a methanol vs diesel reformer comparison, because the diesel reformer approach would negate the need for storage of an additional fuel, methanol, on board the submarine. TKMS built a small 10 kW diesel reformer to support the study. The study conclusions were instructive. The diesel reformer was less efficient because diesel has a hydrogen to carbon ratio of only two to one, whereas methanol has a hydrogen to carbon ratio of four to one. The diesel reformer also needs to run at around 850 degrees which implies heat inefficiency as compared methanol. The higher temperature also means a longer start-up time than the methanol reformer. Finally, unless the diesel carried by the submarine is sulphur free, and standard diesel is not, the required sulphur purifier at the reformer output would likely take up considerable space (as big as the reformer itself). The idea was abandoned.

Public domain information shows DCNS [now called Naval Group] have abandoned their MESMA AIP solution on the Pakistani Agosta 90s and will use a diesel reformer/FC solution on the Shortfin Barracuda. [No supporting detail seen to date.]

Further on the French FC, it appears as though two options are on the table; a PEM or Solid Oxide FC (‘SOFC’) type. If a SOFC is chosen, noting they offer good energy conversion efficiency, long life and operating cost advantages, other drawbacks need to be addressed. Most of these drawbacks relate to the high 600 to 1000°C operating temperature which brings hot exhaust issues and brittleness related shock resistance problems.

Novelty, complexity and uncertainty put this solution’s inclusion in the French package as high risk. Even if the technical challenges of the diesel reformer and FC are solved, the enemy of the DCNS development will be schedule. DCNS are believed to have started their reformer/FC work back around 2006/7 and announced it as a future solution in 2008 as part of their SMX 24 concept design. [1] It is instructive that the Germans have developed and perfected their reformer/FC solution over four decades. It is also worthy of note that the Spanish have had issues with their S-80 submarine ethanol reformer/FC solution and have announced that the first S-80 will now be fitted-for-but-not-with AIP.[2]

The Japanese will not offer up an AIP solution, rather fill any potential AIP space with additional Li-Ion batteries. It is believed this decision stems from their experience with the inefficiency of the Swedish origin Stirling AIP solution. All things considered with respect to reported Stirling engine maintenance overheads and the lack of differential between the Stirling energy density and the Li-Ion energy density, the decision is likely valid.

However, the energy-density differential between the DCNS and TKMS FC and the Japanese Li-Ion’s is large, giving the Japanese solution a poorer indiscretion ratio than the Europeans’ FC approach. It is known that the Japanese originally approached TKMS about adopting their FC AIP solution, but the adoption of the German technology was problematic for two reasons; firstly, the reformer necessary for the larger Soryu submarine was not mature at the time and TKMS/Siemens were not inclined to transfer knowledge of what they considered to be the ‘crown jewels’ of their submarine program. Whilst Li-Ion may have advantages in transit situations, which is why the French and Germans have Li-Ion as part of their solutions, the FC provides the advantage where it really counts; in the operational area. Whilst an all Li-Ion Japanese solution may have advantages with respect to transiting, it means little if the boat is then sunk upon arrival in its assigned patrol area.


[1] The possibility of French DCNS progress is recorded in a DCNS article of 13 October 2016 for Euronaval 2016: “FC2G AIP – Fuel Cell: Second-generation Air-Independent Propulsion. DCNS has developed the 2nd generation AIP system using fuel-cell technology. FC2G AIP provides the best possible dive autonomy in total safety and easy support.”

[2] Spain's problems are covered in IHS Jane’s article of 24 January 2017, which indicates: “Spain's first S 80-class submarine will not be fitted out with [AIP] as development of the system will not be ready in time, according to the admiral in charge of Maritime Action (Almart)...He also said he was not sure which of the four new boats would be the first to be fitted with the AIP system.”


Josh said...


To some extent the mission and environment of the SSK will drive the indiscretion rate requirement. As you already noted, AIP is largely useless for transit - it has neither speed nor endurance. Submarines with long distance patrols, notably JMSDF and RAN, will benefit disproportionally from shorter deployment times by substituting batteries for an AIP system. The other thing to consider is to what extent an increased indiscretion rate on patrol is actually dangerous, considering likely opponents and their wide area ASW* capability. If your primary opponent is the USN, then you can expect a largely 'blue sky' with capable MPAs. There also potentially are SSNs capable of rapidly relocating if they detect a snort or are informed of one via IUSS (satellite communication, VLF, sea web, buoy from ship/plane, etc). So for instance a PLAN Song class snorting in the SCS can hardly feel safe that the snort won't be detected and that there won't be an asset in range to begin a hunt before the boat can clear datum. If your opponent is the PLAN, you might with some confidence conclude that increased time on station was worth a higher indiscretion rate, because their ability to perform wide area ASW is far more limited even inside the SCS and outside the first chain is practically irrelevant. They are just deploying their first MPA, and one can expect them to have problems establishing ASW doctrine and training even if the physical equipment is sound (which seems unlikely given their total lack of experience with MPAs). The PLANs ability to deploy MPAs also likely would be limited by USN CVs and local land based fighters making operations dangerous to impossible (and the new Chinese airfields in the Parcels likely have the same effect on USN MPAs). PLAN nuke boats likely don't have the sensors or communication systems to make them as much of a threat, even if they weren't nosier to begin with. Certainly they are few number in any case.

So from that point of view, AIP might have a reduced significance, especially given a lower snort rate required by LIB batteries. From the figures given on one of the other threads it appeared not only is the total charge greater but the charge rate is superior as well, which would mean that snorts could be both less frequent and shorter in duration.

* I define 'wide area ASW' as basically ASW not involving task forces/convoys of any type - ie, searching for boats in a large open space as opposed to local ASW defending specific assets. In the case of the latter indiscretion rate shouldn't matter; a reasonably full charge should allow an engagement and egress (especially with LIBs).


Anonymous said...

Hi Pete

More than 10 years ago, Japan Ministry of Defense demonstrated that prototype LIB for submarine had howed higler energy density (more than twice) and longer cycle life (more than 1.5 times) than those of LAB. Current LIB for submarine may show improved performance.

LIB is rechargeable by diesel generators and LOx can not be supplyed, indiscretion ratio becomes worth with consumption of oxydizer (Lox) for AIP-LAB submarine.

FC-LIB submarine will show high performance, but cost of LIB/FC is very high. As shown budget of LIB-Soryu, LIB is very expensive. Cost of FC seem to be expensive, too. FC adopts Platinum electrode which deteriorates with time and is easily poisoned by contamination. FC must be exchanged at deterioration of Platinum electrode.

Consumption of LOx results in weight change which is adjustable. As buoyancy of submarine is small, such weight change is obviously undesirable factor in operation of submarine.


Peter Coates said...

Hi Josh

Yes its very true that an SSK's mission influences its indiscretion rate and as you say its mission also influences whether AIP of any type would be a help or present a problem.

Indeed the longer the mission with more need for longer range rapid transit the less useful for the SSK to haul AIP machinery and AIP propellents – especially the heavy-baulky LOX which I believe all AIP systems need. So Japan with perhaps a transit of 2,000nm each way is a marginal AIP user - phasing AIP out. Meanwhile the RAN, maybe 3,000nm each way, has never used AIP and may not use it in the Shortfins.

AIP has been most developed by the countries which use AIP for their own navy’s for shorter range mission requirements (ie. Sweden and Germany). China, which has developed AIP in parallel may heavily use AIP for missions around Hainan and Taiwan as well as East China Sea and Sea of Japan missions.

Non-Japanese navies with SSKs (including Russia) are studying Japan’s LIB introduction process very closely. If Japan succeeds other navies will develop LIBs capabilities.

I agree that 'wide area ASW' (from SOSUS, other sensors, to satellites) plays a critical part in the highly complex AIP, battery-types and indiscretion vs mission calculations.



MHalblaub said...

Dear Josh,

I can see no reason why LIBs can't be used with an AIP. So a shorter snorting time for transit could also be achieved but is limited by installed Diesel power to recharge the batteries. According to different sources Navantia is going to use LIBs and AIP on S-80 (no AIP at the moment - seems not so easy or to heavy to resurface).

BTW the idea to use fuel cells on a submarine was perused in Germany since the late seventies. Some may remember "Apollo 13". An oxygen tank of the fuel cell system exploded. The article mentioned above stated just Siemens started with fuel cells in the early eighties.

LIBs for a submarine with AIP could be rather small by just keeping LAB battery capacity.

There is a big difference between the place where the energy is stored. Batteries are located inside the tight pressure hull while the reactants for an AIP could all be stored on the outside. Type 214 stores LOX inside the pressure hull but that is not so preferable. Maybe it was an easy solution at time to transform the Type 209 like Type 209PN.

On the other side a fuel cell system is rather small inside the pressure hull:
(Just the 9 squares)
A methanol reformer is about the same size.


Like for Diesel the density of methanol is about 0.8 kg/L.
Flooding diesel tanks with water at 1.0 kg/L results in a downforce. Empty methanol or oxygen tanks provide buoyancy but methanol tanks could be flooded.

The chemical process to reform hydrogen from methanol requires water. I do not now how sensitive a reformer is to salt but due to the chemical process purified water could flood empty methanol tanks without problems. Pure water is produced by fuel cells.

CH3OH + H20 -> CO2 + 3 H2 (reformer process)
3 H2 + 3 O -> 3 H20 (fuel cell process)

For one methanol molecule the complete process delivers 2 water molecules. Mind that one H20 is used in the first cycle.

Molar mass for methanol is 32 g/mol. Water 18 g/mol. Oxygen 16 g/mol.
So for 32 g methanol 36 g of water are produced. Due to density differences 1 liter methanol just produces ~ 0,9 liter of water. The process still has a weight loss of 44 g/mol to to carbon dioxide dissolved into the sea. But 44 g/mol is less than half of reactants involved 98 g/mol ( 32 + 18 + 3 x 16).

So about 90 % of the methanol tanks could be flooded with pure water and 10 percent with sea water. The sea water tanks could be purged for use by the pure water of the other tanks to use fill them again with methanol. So just about 40 % of the complete reactant mass has to be compensated by additional ballast tanks.

The need for additional tanks is even less. It depends on ratio of Diesel fuel to reactants. Empty Diesel tanks can compensate additional buoyancy because water is 20 % heavier than Diesel oil. With a ratio of Diesel to reactants of 2:1 no additional ballast tanks should be required.

World wide methanol production is more than 40 million ton a year. Price about 350 €/t and oxygen is cheaper. Both reactants are nearly world wide available.

I didn't get the point about Japan. They have rather short transit and long times on station. A working AIP solution would be far more ideal.


Peter Coates said...

Hi Anonymous [at 1/3/17 10:30 AM]

With Japan now wanting to sell subs to foreign buyers - I imagine TKMS, DCNS and Kockums will be even less willing to share technology with Japan.

Yes LIBs make more sense than LABs-AIP if Japan has regular long distance missions.

Interesting that Japan wants to keep new submarine costs low while Australia has effectively made the Shortfin submarine costs high ("$50 billion").



Anonymous said...

Hi Pete

According to HDW [1], methanol are mixed with water from FC and evaporated and fed to the steam reformer, and methanol and oxygen are fed to the burner for steam. HDW never adds water or sea water into methanol tank.

I heard AIP was unpopular with Japanese submariners. According to ex-commander of submarine fleet, after depeletion of oxygen AIP-submarine has to return, but, LIB-submarine can recharge after consumtion of battery energy.

GS YUASA is going to place lithium sulfur battery (LSB) on the market until 2020. Application of LSBs to submarine may be possible by or aound 2030. Game is changing.

[1] http://juser.fz-juelich.de/record/135470/files/HP4a_9_Krummrich_rev0605.pdf
Page 216, Fig.2 Overview of Methanol Reformer System


Josh said...

@ MHalblaub:

LIB doesn't exclude the use of AIP of any type, be it fuel cell, Stirling, etc. But depending on the environment and mission of the boat, it may not be worth the weight, volume and expense in the boat as opposed to either more batteries, more installed diesel power (compare Collins installed power to Kilo), or a smaller, less expensive boat. The RAN for instance has never shown much interest in AIP plants at any juncture, I believe primarily for the reasons I stated. An FC arrangement requires liquid oxygen and hydrogen, or a reformer and methanol in the German set up, all of which take up space and money, plus the additional hazard of handling and storing LO2. For coastal submarine that spends most of its time on patrol, close to a coast, which can expect a lot of Russian air traffic over it - that probably makes the most sense. For navies with much greater transit times in more open environments than the Baltic it is less cost effective. This isn't to say it technically can't be done or that it wouldn't be a nice to have, money not being an object, just to say there is logic to a design that skips AIP altogether and relies on a traditional D/E arrangement. That LIBs have a longer battery life and seem to charge faster (?) would tend to emphasize that design philosophy.


Anonymous said...

Not much more than this on the internet. Interesting though.

Peter Coates said...

Thanks Anonymous [at 2/3/17 1:16 AM]

"Fuel Cell Methanol Reformer System for Submarines" by S. Krummrich of 2010 still seems current. It is very informative.

Page 216, Fig.2 Overview of Methanol Reformer System



MHalblaub said...

Dear Anonymous (2/3/17 1:16 AM),

I was not talking about mixing Methanol with water in the tanks and also not about what HDW does.

I thought about filling up empty tanks with FC water.
Later on a few could be also filled up with salt water. These have to be purged with FC water for reuse. A few drops of FC water in the methanol tanks are of no matter.

"According to ex-commander of submarine fleet, after depeletion of oxygen AIP-submarine has to return, but, LIB-submarine can recharge after consumtion of battery energy."
Even more than that: they have to.
A Diesel-whatshowever submarine also has to return to some kind of base for refueling diesel. LOX and methanol can easily stored and transferred by a tender just like diesel.
Pumping LOX from one truck to another:

The PDF by fz-juelich.de shows also how small the reformer is (see figure 4). Even by estimating a big Type 216 for curvature.


Anonymous said...

Hi Pete

Following is just my imagination.

As mordern submarine has optimal structure/arrangement, I assumed three submarine models based on Soryu as a common platform and very roughly estimated their performances at submerge.

Case 1 is submarine X (4 diesel generators, LABs, 12m longer than Soryu, No AIP) with 3-4days of maximum submerged period at 4knot/h. Actual maximum submered period is 1-1.5 days.

Case 2 is submarine Y (2 diesel generators, LIBs, same length with Soryu, FC) with 30 days of maximum submerged period at 4knot/h by FC.

Case 3 is submarine Z (2 diesel generators, ITO (lithium titanate)-LIBs, 6m longer than Soryu, No AIP) with 5days of maximum submerged period at 4knot/h. Actual maximum submered period is 4.5 days.

Order of performance is Y > Z>>X. As performance of X is too inferior to those of Y and Z, even most advantageous terms do not provide winning of X in tender. If X equips with AIP, there is a chance of winning.

I believe Shortfin will equp with AIP. Order of perfornence is X(with AIP)=Y>X. Now, advantageous terms provide winning of X. One of causes of J-submarine defeat may be offer of ITO instead of NCA which gave the impression of lack of enthusiasm.

Again, this is just my imagination.


Peter Coates said...

Hi Anonymous [at 4/3/17 9:57 PM]

It is interesting that Shortfin may be equipped with AIP.

A build starting 2026 may permit DCNS time to develop/acquire from Germany efficient Reformer/FC AIP and perhaps LIBs from Japan.

Such a submarine would be very formidable, even operating from Fremantle to the East China Sea without diesel refueling.



Josh said...


As far as I know AIP wasn't part of the RAN requirement and there were no plans to equip it. Is this no longer the case?


Peter Coates said...

Hi Josh [at 6/3/17 4:37 AM]

No. I've neither heard nor read about any RAN interest in AIP for the Collins or the Shortfin.

However the long timelines towards build (from 2026) for the Shortfin allows in uncertainty about final propulsion fit out. No nuclear unfortunately.

In technology predictions much also dependends on Australia's healthy relations with the US and/or possibly hostile relations with China by 2026.

If Japan succeeds in its LIBs then the slower and parallel DCNS LIBs program may produce LIBs for Shortfin.

Likewise if DCNS has advanced Diesel fed Reformer/FC that is mature and efficient by 2026 then the RAN may consider that technology.



Anonymous said...

Hi Pete

As France exports important weapon system to Chinna neglecting plea of Japan and is rival of USA in weapon business. Japan and USA do not offer latest technology such as LIBs and revolutional optics. France has crossed line.