Hydrogen-oxygen fuel cell system. (Diagram courtesy of http://webberswarships.ca/styled-9/index.html )
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MESMA closed-cycle steam turbine
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Stirling-cycle heat engine with external combustion
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Closed-cycle diesel engine? (Diagram courtesy of http://webberswarships.ca/styled-9/index.html )
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Diesel-electric engine for submarine, which can use any of the AIP technologies above.
Descriptions of the strengths and weaknesses of each AIP technology is on this website at
If-when Australia chooses an air independent propulsion (AIP) system for the long awaited Future Submarine Australia will have several technologies (above) to decide on. Perhaps Australia might choose no AIP if Lithium-ion battery technology is considered adequate.
SUBMARINE
TRENDS IN ASIA PACIFIC: AIR-INDEPENDENT PROPULSION A GAME CHANGER? – ANALYSIS
JANUARY
29, 2013
By
RSIS
The contending strategic realities of the Asia-Pacific region compel states to
adopt innovations of their rivals. This is the case for new classes of
conventional submarine designs, which incorporate an array of innovative
technologies in order to maximise their survivability and lethality in diverse
maritime operations.
By Michael Raska
WHILE EUROPE and North America remain
key submarine markets, China’s ongoing military modernisation coupled with
contending international relations in the Asia-Pacific will increasingly drive
submarine procurement in the region over the next decade. In 2011, the total
submarine market in Asia-Pacific is estimated at US$4.4 billion, and for the
next decade, submarine expenditures are projected to US$46 billion.
With
changing strategic realities, Asian navies aim to become increasingly flexible,
and capable of varying mission profiles: from countering traditional coastal
defence missions to protecting sea lanes and communication lines.
Simultaneously, submarines are increasingly valuable strategic resource for
both electronic and signal intelligence. To enhance the varying operational
capabilities, increase submerged endurance and stealth, installing viable
Air-independent propulsion systems is thus becoming a strategic necessity.
Advantages of AIP systems
Designed to enhance the performance
of modern conventional (diesel-electric) submarines AIP is a key emerging
technology that essentially provides a “closed cycle” operation through a
low-power electrical source supplementing the battery, which may extend the
submarine’s underwater endurance up to two weeks or more.
AIP systems close the endurance gap
between nuclear and conventional submarines, and mitigate increasing risks of
detection caused by advanced anti-submarine warfare technologies – from modern
electro-optical systems and surface radars to magnetic sensors, active and
passive sonars, and airborne surveillance radars. Advanced AIP technologies
thus promise significant operational advantages and tactical flexibility.
In theory, there are four primary AIP
designs currently available: (1) closed-cycle diesel engines; (2) closed-cycle
steam turbines; (3) Stirling-cycle heat engines with external combustion, and
(4) hydrogen-oxygen fuel cells. Each provides a different solution with
particular advantages as well as limitations in relation to performance,
safety, and cost factors.
Since the early years of the Cold
War, while major naval powers shifted to nuclear propulsion, smaller navies –
particularly in Europe (Germany, Sweden, Spain, Italy and France) continued to
develop and rely on conventional diesel-electric submarine fleets, given their
lower cost and operational relevance for coastal defence. Traditionally,
however, these submarines were highly vulnerable to various types of sensors –
acoustic, visual, thermal and air – particularly when running on engines.
AIP systems in Asian navies
On the other hand, when running on
batteries, these submarines became very quiet and difficult to detect, yet
their battery capacity, discharge rate, and indiscretion rate (the ratio of
diesel running time to total running time) substantially limited their
underwater endurance. To overcome these baseline limitations, naval innovation
in propulsion technologies over the past two decades has shifted toward AIP
systems.
There is a variance, however, in the
procurement of AIP systems in select Asian navies. For example, the only AIP
steam-turbine system currently available is the French “MESMA” (Module
d’Energie Sous-Marine Autonome) module, operational on Pakistan Navy’s two
Agosta 90-B class submarines.
Swedish-Kockum designed Stirling AIP
technology is installed on Singapore Navy’s two Archer–class submarines, and
Japan’s new Soryu-class submarines. The Chinese PLA Navy’s Type 041 Yuan and
Type 043 Qing class submarines are also reportedly using Stirling technology.
Meanwhile, the Republic of Korea Navy has ordered nine Type 214 submarines with
German HDW AIP fuel cell technologies. Three first batch models of the new Son
Won-Il class had entered service since 2007, and six second batch models will
enter service from 2012.
Limitations and constraints
Notwithstanding the diverse AIP
technologies, the overall effectiveness of each system will depend on how well
it is integrated with other critical systems that ensure optimal submarine
functions: power systems, sensors systems, safety systems, navigation systems,
command, control, and communication systems, weapons systems, and climate
control systems. In this context, any critical failure of an AIP during a
combat mission or contested areas will mitigate survivability factors as well
as tactical options.
Indeed, each AIP system design comes
with an array of technological limitations, vulnerabilities, and risks,
particularly in submerged operations – from the specific acoustic signatures
produced by select AIP systems in specific operating regimes, to technical vulnerabilities
in storing oxidizer/fuel, as well as their maintenance regime. At the same
time, new anti-submarine warfare sensor technologies may provide viable AIP
countermeasures.
Ultimately, AIP-related technological
innovation and breakthroughs may not guarantee operational success – strategy,
operational concepts, tactical development, leadership, training, and morale
will continue to play as important role as emerging technologies and their
operational capabilities.
Michael Raska is
a Research Fellow at the Institute of Defence and Strategic Studies, a
constituent unit of the S. Rajaratnam School of International Studies (RSIS),
Nanyang Technological University in Singapore.