Naval Group Achieves Breakthrough with its FC2G AIP System

Naval Group announced that they achieved a breakthrough with their proprietary FC2G AIP system for submarine: The company demonstrated an 18 days submerged patrol representative of operational conditions.

FC2G AIP stands for Fuel Cell 2nd Generation Air Independent Propulsion. It consists in a module packaged as a dedicated hull section about 8m in length and suitable for either new-build boats or modernization programs.

The long-term (land-based) test was conducted at the Naval Group site of Indret near Nantes in March, with a true submarine operational profile. The test confirmed a submerged duration of up to three weeks, the optimization of the maintenance cycle and the performance of the major components of the system.

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This patrol of 18 days has been conducted in representative operational conditions such as:

  • 18 days continuous electrical production from diesel oil reforming

  • high pressure (compatible with maximal immersion of the submarine)

  • close to submarine environmental conditions and safety requirements

  • connected to submarine batteries

  • controlled and monitored by only one operator as it will be on board through the Integrated Platform Management System (IPMS)

Along this patrol, the following results and developments have been achieved:

  • Reduction of signature thanks to H2 recovery efficiency improvement (above 99%) and trials of silent pumps

  • Demonstration of capability to allow several starts & stop per patrol according to submarine typical missions.

  • Reduction of the maintenance activities thanks to catalysts and on diesel oil reforming system endurance improvement.

  • Improved Fuel cells (compactness, easy maintenance, low fuel consumptions)

  • Fuel cells lifetime increase thanks to a purity of more than 99,999% of the Hydrogen produced (better than H2 storage solution)

  • Industrialization studies confirm that the Naval Group AIP system can be integrated whatever the diesel electric submarine (SSK).




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FC2G AIP consists in a module packaged as a dedicated hull section about 8m in length and suitable for either new-build boats or modernization programs.

Naval Group’s FC2G AIP: What is it ?

Fuel cell AIP based on metal hydride storage have been designed for small submarines without ocean going ambitions. Hydride cylinders were placed outside the submarine, representing a risky challenge in terms of submarine architecture and weight balance. To illustrate it simply out of the 130 to 160 tons of hydrides transported by a FC system, less than 2% represents hydrogen that can really be used in fuel cells, which is an inefficient and costly rate.

In addition, there are significant implications of the logistical support that must be deployed to refuel submarines with ultra-pure hydrogen and oxygen. It involves special facilities for the treatment of gas; trucks conditioned in compliance with the strict regulations for transporting hydrogen; qualifications and procedures to keep purity of hydrogen and the integrity of the submarine and its crew to be guaranteed: a complex and expensive logistical chain in itself, which, is not available in any ports.

Safety must be paramount during submarine operations. The recent events with the loss of the Argentinian TR-1700 submarine reminded it dreadfully to everybody. This is why the storage of hydrogen on board is considered as a permanent risk for the submarine and its crew.

As a way of mitigating those problems, an onboard hydrogen production using fuel reforming was adopted by the main submarines shipyards, considering ethanol, methanol or diesel-oil. For this, the challenge was to select a fuel which would respond not only to an operational requirement but which also complies with the safety standards specific to the construction and operation of submarines, and particularly gives the maximum protection to the crews. At the same time, it was necessary to provide a comprehensive response to what it means to logistically support an AIP system, in other words, on-board and ground facilities for treating and providing the respective fuels, and support during the life cycle of the submarine.

This new step has considerably improved various aspects going from safety to operational use. The equilibrium between systems that store energy and those that produce are therefore bringing significant benefits for navies such as:

  • No more constraints in terms of sea water temperature, avoiding hydrides heating process.

  • Avoid hydrides pollution with significant cost consequences during life cycle.

  • A safer system in terms of hydrogen management, during submarine time at sea and alongside.

  • No more numerous sub systems distributed on all the parts of the submarine, due to the fact that all components are now located in a dedicated section.

  • No more logistic constraints refueling hydrogen.

In order to accomplish all the operational and logistic needs on reforming process, the selection of the adequate fuel was the big challenge, and five criteria’s were used, taking into account both safety and performance:

a) Safe storage
b) Energy and density of hydrogen in the selected fuel
c) Complexity of H2 production
d) Integration volume
e) Availability

After analysis (considering several test and safety standards) it appeared that diesel-oil was the most suitable option:

  • It has the highest point of ignition, decreasing the risk of fire (safety).

  • It is the least toxic fuel for the exposition of the crew (safety).

  • It is easy to handle in terms of loading and unloading procedures on board (security/logistics).

  • Crews are proficient at using and handling it (safety/training).

  • It has a better energy response and hydrogen density (performance).

  • It has a worldwide availability with high purity standards (logistics/ operational).

The FC2G AIP has needed decades of development and tests and is now “ready to sail”. There are advantageous both in terms of operations and logistics for users, considerably reducing the indiscretion rate, as well as not being tied to the limitations associated with the storage of hydrogen on board, in terms of safety and costs.

It is important to consider that this new generation of AIP is like another ordinary source of energy for a submarine. Commanding Officer in combination with the batteries will be able to accomplish the ever complex and challenging submarine warfare in a completely different mindset. The advantages are so important that navies are naturally looking forward to get this new generation AIP to avoid all the issues of the oldest systems.

Naval Group’s FC2G AIP: How it works ?

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The Hydrogen Production Process relies on 3 steps:

Step 1 : Gas generation, in the Reformer
Fed with Diesel Oil, Oxygen and Steam (which is recycled in the process), the Reformer converts this mixture into a Hydrogen-rich synthetic gas.

Step 2: Hydrogen Yield Increase and Carbon Monoxide Conversion, in the Shift reactor
Following the Reformer, the Shift reactor drives a “Water-gas Shift” reaction, converting Carbon Monoxide into Carbon Dioxide, along with the conversion of water into Hydrogen. Consequently, it increases the Hydrogen content of the synthetic gas to the maximum available, along with the almost elimination of Carbon Monoxide.

Step 3: Hydrogen purification, in the Membrane
Using unique properties of special alloys, the membrane extracts hydrogen from the synthetic gas to feed the Fuel Cells with ultra-pure hydrogen, without the need of storage.

Hydrogen is thus produced on-board and on demand to be used in the next step:

Electricity Production, in the Fuel Cells
Based on industrial technologies and adapted for submarine application, the Fuel Cells developed for the FC2G AIP combine the hydrogen supplied by the Hydrogen Production Process (1 2 3) to Oxygen which is stored onboard. So as to improve durability and cost, the Fuel Cells mixes Oxygen with Nitrogen before the core of the System, allowing using standard Air Proton Exchange Membrane Fuels Cells technologies.

Naval Group’s FC2G AIP: Main Components


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1- Reformer
Goal: To produce hydrogen-rich gas from diesel oil.
Main feature: Naval Group is the 1st in the world to succeed in diesel oil reforming with submarine constraints.

2- Innovative shift
Goal: To increase Hydrogen yield & remove CO from gas produced by the reformer.
Main features: High compactness and high thermal efficiency.

3 – High tech purification membranes
Goal: To supply the Fuel Cells with ultra pure Hydrogen.
Main features: Innovative, high performance, quiet, perfect for submarine low acoustic requirements.

4 – PEM Air fuel cells
Goal: To produce electricity from H2 & O2.
Main features: Latest PEM fuel cell technology, robust and compact, high efficiency, easy maintenance.

5 – Oxygen module
Goal: To store and provide O2 to the AIP system and to the submarine for crew breathing.
Main features: Liquid Oxygen storage, standard Oxygen quality, easy to supply.

All the components are integrated on a dedicated section with elastic mounting and suspended cradles to avoid any impact on the acoustic signature.