Brief Description about AIP Tecnology and Torpedos

1. Air Independent Propulsion(AIP) Technology
Submarines and Torpedos
Bala Vignesh D
ME/SER10010/17 1

2. Submarine - Introduction
 Submarine is an naval vessel that is capable of propelling itself beneath
the water as well as on the water’s surface.
 Submarines were first widely used during World War I (1914–1918), and
now in many navies large and small.
 Uses
 Military - include attacking enemy surface ships, attacking other
submarines, aircraft carrier protection etc…
 Civilian - marine science, salvage, exploration and facility inspection
and maintenance.
 perform more specialized functions such as search-and-rescue
missions or undersea cable repair.
 used in tourism, and for undersea archaeology.
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3. Turtle
 World's first submersible with a documented record of use in combat.
 It was built in 1775 by Americans as
a means of attaching explosive
charges to ships in a harbour of
against British Royal Navy.
 hand-operated controls and foot
pedals to propel the submersible
into position with very low oxygen
concentration mission made
difficult.
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4. Direct Drive Engines
 In this direct-drive power system, the diesel engine is directly
connected to the propeller shaft with combination electric
motor/generator in between.
 A clutch connects the engine to the motor/generator. A second
clutch connects the motor/generator to the propeller shaft.
 When the engine is connected to the motor/generator, the m/g
functions as a direct current generator. Its output is directed through
the switchboard, with the switches on charge, and into the batteries,
keeping them charged.
 Throwing the switches to the battery position takes power from the
batteries and directs it into the m/g, which now functions as a motor,
driving the propeller shaft.
.
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5. Direct drive Engines
 Advantages:
• smaller submarines could be built in greater numbers.
 Disadvantage:
• limited to one or two engines
• relatively short-range designs of World War I
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6. Diesel-Electric Submarines
 Hybrid Vehicles – Run with batteries while submerged and diesel
engines while on surface
 On surface, they have a large network of batteries which are
charged by the diesel generator.
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7. Diesel-Electric Submarines
 Once they charge their batteries, they dive into the ocean and run
silently on battery power with the diesel generators shut down. After
running for a few days underwater, the battery gets drained in 4 to 5
days and these submarines have to surface again to recharge their
batteries
 also referred to as SSK (Sub Surface Hunter-Killer) by US Naval.
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8. Nuclear Submarines
 Also fall under the category of Air independent propulsion
 The large amount of power generated by a nuclear reactor allows
nuclear submarines to operate at high speed for long periods of
time; and the long interval between refuelling grants a range limited
only by consumables such as food.
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9. Motor types
 Main Electric Propulsion Motor (EPM): The propulsion plant is
distributed over two watertight compartments. The main electric
propulsion plant is located in the first compartment of the propulsion
plant. It is driven by the electric power produced by the batteries. A
DC powered motor is always used, as more power losses are
observed in AC motors.
 Endurance Motor: In order to increase the endurance of the
submarine, during war times, the submarine needs to economise on
the consumption of fuel. In such a scenario, the propeller is driven
by the economic motor.
 The endurance motor is located in the second compartment of the
propulsion plant, so that either of the two motors can be operated in
case of flooding in one of the compartments.
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10. Why do we need AIP?
 Snorkel: travelling just below the surface of the water with the periscope
and the diesel generator exhaust pipe above the water surface.
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11. Why do we need AIP?
 It exposes them to detection by enemy radars and makes them an easy
target for hostile anti-submarine assets.
 Although modern snorkels are coated with radar absorbing paint and
have a stealthy shaping, they are still detectable by high resolution
radars.
 There are also sensors called diesel sniffers which can detect the
exhaust emissions of the submarines diesel generators while snorkelling.
 A submarine which needs to surface every day, loses its element of
surprise and increases its vulnerability to hostile anti-submarine assets.
 Although nuclear submarines offer far better endurance and speeds, they
are unsuitable for the shallow littoral waters and are very expensive. 11

12. Why do we need AIP?
 Also diesel submarines possess the advantage of being able to switch
off their engines completely and lie in wait unlike nuclear submarines
whose reactors cannot be switched off at will.
 Hence we need a system which can allow diesel-electric submarines to
recharge their batteries without running their engines to continue sailing
underwater and retain the element of surprise by remaining undetected.
 The system should also allow the SSKs to retain their extremely low
noise signatures and should not compromise on the performance of the
submarine.
 The system which permits all this is Air Independent Propulsion (AIP).
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13. AIP: Introduction
 Air-independent propulsion (AIP) is an marine propulsion technology that
allows a non-nuclear submarine to operate without access to atmospheric
oxygen, which vastly improved the underwater endurance of these
submarines and gave them a distinct advantage
 AIP does not normally provide the endurance or power to replace
atmospheric dependent propulsion, but allows longer submergence than a
conventionally propelled submarine
 The types of AIP systems are
 Closed Cycle Diesel Engines
 Closed Cycle Steam Turbines
 Sterling Cycle Engines
 Fuel Cells
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14. Closed Cycle Diesel Engines
 Liquid oxygen (LOX) is stored in tanks on board the submarine and sent
to the diesel engine for combustion.
 Since they need to simulate the atmospheric oxygen concentration for the
engines to run safely without getting damaged, the oxygen is mixed with
an inert gas (usually argon) and then sent to the engine.
 The exhaust gases are cooled and scrubbed to extract any leftover
oxygen and argon from them and the remaining gases are discharged into
the sea after being mixed with seawater.
 The argon which is extracted from the exhaust is again sent into the diesel
engine after being mixed with oxygen.
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15. Closed Cycle Diesel Engines
 Advantages:
• comparatively cheaper
• simplifies logistics by the use of standard diesel fuel.
 Disadvantage:
• storing of liquid oxygen safely on board the submarines.
• Limited LOX fuel storage space
• highly prone to fires and subsequently discontinued their usage.
• Running diesel can be noisy.
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16. Closed Cycle Stream Engines
 Steam turbines make use of a source of energy to heat water and convert
it into steam in order to the run the turbine.
 In nuclear powered submarines, the reactors provide the heat in order to
convert water into steam. But in conventional closed cycle steam
propulsion, a non-nuclear energy source is used to do the same.
 The French MESMA (Autonomous Submarine Energy Module) is the only
such system available and it uses combustion of ethanol and oxygen
under high pressure as energy source to generate steam.
 The steam generated is the working fluid and is used to run the turbine.
The high pressure combustion allows the exhaust carbon dioxide to be
expelled outside into the sea at any depth without making use of a
compressor. 16

17. Closed Cycle Stream Engines
 Advantages:
 higher power output when compared to the alternatives which
allows higher underwater speeds
 Disadvantage:
 Very Low efficiency
 Rate of oxygen consumption is very high
 very complex
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18. Sterling Cycle Engines
 The source of energy used here is typically LOX as oxidizer and diesel
fuel, which is burnt in order to generate heat for the working fluid. The
exhaust is then scrubbed and released into the seawater.
 A source of energy is used to heat the working fluid, which in turn moves
the pistons and runs the engine. The engine is coupled to a generator,
which generates electricity and charges the battery.
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19. Sterling Cycle Engines
 Advantages:
 Easy availability of diesel fuel and low refuelling costs when
compared with Fuel Cells
 Quieter than MESMA
 Disadvantage:
 Relatively noisy when compared to Fuel Cells due to the presence
of a large number of moving parts.
 Bulky when compared to Fuel Cells.
 The operating depth of a submarine using Sterling AIP is limited to
200 m when AIP is engaged.
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20. Fuel Cells
 A Fuel Cell is a device which converts chemical energy into electricity.
This is done using a fuel and an oxidizer. A typical fuel cell converts
Hydrogen and Oxygen into electricity, with water and heat released as by-
products.
 This is done by an electrolytic cell which consists of two electrodes, one
positive (anode) and the other negative (cathode), separated by an
electrolytic barrier.
 The reaction between the cathode and anode produces an electric
current, which is used to charge the batteries. A chemical catalyst is used
to speed up the reactions.
 Phosphoric Acid Fuel Cells (PAFC) and Proton Exchange Membrane Fuel
Cells (PEMFC) are presently used in submarines. 20

21. Fuel Cells
 Advantages:
 High stealth as Fuel Cells have almost no moving parts, which
significantly reduces the acoustic signature of the sub.
 Achieve an efficiency of over 80% under certain circumstances
 Can also be scaled easily into large or small sizes depending on
the displacement of the submarine.
 Easy to develop
 Hydrogen Fuel Cells are also very environment friendly as they
generate no exhaust fumes, which in turn eliminates the need to
have special exhaust scrubbing and disposal machinery.
 Disadvantage:
 Expensive and complex.
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22. Advantages of AIP
 Greatly increases their underwater endurance, allowing them to
continuously stay submerged for weeks without surfacing.
 Avoid the high cost of nuclear power
 Increase submarine range.
 Retain the advantages of Conventional diesel electric submarines.
 However AIP doesn’t give any advantage other than increased
underwater advantage and it should not be assumed that AIP-
equipped submarines will always defeat their non-AIP equipped
counterparts.
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23. Limitations of AIP
 Other than Fuel Cells, the 3 remaining technologies have a lot of
moving parts which generate noise. This is not desirable as
quietness is very essential for all submarines.
 Even though Fuel Cell AIP has many advantages, it is extremely
expensive to procure and maintain them.
 Submarines which use AIP need to sail at speeds of less than 10
kts in order to achieve exceptional endurance of 14-18 days as
advertised. In comparison, a nuclear powered sub can travel for an
unlimited distance at 30-35 kts without sacrificing endurance. So
AIP equipped submarines cannot replace nuclear submarines when
it comes to blue water or extended period operations.
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24. Combat Scenario
 AIP equipped submarine can roam near a strait, wait for its target to
approach. The sub will be running at ultra-quiet speeds of 2-4 knots
for several weeks and then attack the target when it appears, using
its torpedoes.
 Even though a non-AIP equipped sub can do the same thing, it’s
waiting period, which is very essential for an underwater ambush, is
significantly lesser.
 AIP equipped sub can roam near enemy territory for far longer
compared to a non-AIP sub. Thus in this situation where intelligence
is gathered and spy missions are performed, AIP gives these quiet
diesel subs an advantage by allowing them to loiter for weeks
without the need to surface.
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25. Torpedo - Introduction
 A torpedo is essentially a guided missile that happens to "fly"
underwater which has a propulsion system, a guidance system and
some sort of explosive device, travel several miles on their way to the
target, and therefore they need a propulsion system that can run for 10
to 20 minutes.
 Torpedoes use one of- two techniques for propulsion:
 Batteries and an electric motor -- same technique that any non-
nuclear submarine must use when running underwater.
 Engines that use special fuel -- uses a fuel that either does not need
an oxidizer, or it carries the oxidizer inside the torpedo.
 Hydrogen Peroxide does not need an oxidizer.
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26. Compressed Air
 First successful self-propelled torpedo - used compressed air as its energy
source. The air was stored at pressures and fed to a piston engine that
turned a single propeller.
 It could travel about 180 metres at an average speed of 6.5 knots. The
speed and range of later models was improved by increasing the pressure
of the stored air.
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27. Disadvantage
 Line of air bubbles are produced which easily revealed their
presence to vessels on the surface making them easy to avoid.
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28. Development - Torpedo
 Dry Heaters
 Injecting a liquid fuel, like kerosene, into the air and igniting it shown
better performance than normal compressed air torpedo as air is
heated more and expands even further, and the burned propellant
adds more gas to drive the engine.
 Wet Heaters
 Water was used to cool the combustion chamber of the fuel-burning
torpedo.
 Solved heating problems + allowed additional power to be generated
by feeding the resulting steam into the engine together with the
combustion products.
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29. Development - Torpedo
 Compressed oxygen
 It used pure compressed oxygen instead of compressed air (as it
contains only about 21% oxygen) and had better performance
 However, oxygen systems posed a serious danger to any ship that
came under attack while still carrying such torpedoes.
 Electric Batteries:
 Powered by electric motor which drives the propeller
 Doesn't produce air bubbles (no trail)
 Requires large amount of battery power making it bigger and bulkier
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30. Battery powered Guided Torpedo
 It was powered by a fibre optic cable from an external power source,
as batteries had insufficient capacity and steered by impulses
towards the enemies.
 Its lead-acid rechargeable battery was sensitive to shock, required
frequent maintenance before use, and required preheating for best
performance.
 Modern electric torpedoes such as the Mark 24 Tigerfish or DM2
series commonly use silver oxide batteries that need no
maintenance, so torpedoes can be stored for years without losing
performance.
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31. Battery operated Guided Torpedo
 Advantages:
 wakeless and much cheaper
 avoided tell-tale bubbles
 Disadvantage:
 slower and had shorter range than the conventional
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32. Rocket engine
 Soviet union developed a rocket powered torpedo which could go to speed
of 200 knots per hour.
 It can generate hot gases by heating source from its nose creating a cloud
of stream from the water that’s in front of it creating a thin bubble of gases
as it goes. By travelling through the gas there is far less drag for the torpedo
 Very noisy – no stealth
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33. References
 https://science.howstuffworks.com/transport/engines-
equipment/question419.htm
 http://www.fleetsubmarine.com/propulsion.html
 https://www.drdo.gov.in/drdo/pub/techfocus/oct2000/underwater.htm
 https://science.howstuffworks.com/nuclear-submarine3.htm
 https://www.youtube.com/watch?v=tze6zgrRJKM
 https://defencyclopedia.com/2016/07/06/explained-how-air-independent-
propulsion-aip-works/
 https://en.wikipedia.org/wiki/Air-independent_propulsion
 http://www.marineinsight.com/naval-architecture/different-systems-on-a-
naval-submarine/
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