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Air-independent propulsion (AIP), also known as air-independent power, refers to any maritime propulsion system that enables a non-nuclear submarine to operate without exposure to atmospheric oxygen (by surfacing out or using a snorkel). AIP can be used by non-nuclear submarines to enhance or replace their diesel-electric propulsion systems. While some contemporary submarine reactors depend on naturally circulating coolant, the majority of other navy nuclear reactors use pumps to circulate the core coolant on a continuous basis, causing some detectable noise, making them less stealthy than newer nuclear submarines. On the other hand, non-nuclear submarines powered by battery systems or AIP may be virtually silent.
Air Independent Propulsion Technology
- AIP is a device that makes it possible to charge the batteries even when the boat is submerged. The submarine must surface every three weeks or so even with AIP.
- Submarines are essential of two types: Conventional and Nuclear. The diesel-electric engine of conventional submarines requires daily surface trips to obtain oxygen for fuel combustion. For deep-sea operations, many naval countries, including India, have purchased nuclear-powered submarines.
- AIP can be incorporated into existing submarine hulls by adding an extra hull segment.
- Although the AIP system often lacks the endurance and power to replace atmospheric propulsion, it does enable deeper submersion than a conventionally powered submarine.
- India has been attempting to create its own AIP technology.
- There are various AIP methods available, and India wants the P-75I project to use a fuel cell-based AIP.
- These cells recharge the submarine’s batteries by converting chemical energy into electrical energy.
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Key Features of Air Independent Propulsion System
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- It enables submarines to spend more time submerged. To recharge their batteries, the submarines must surface from beneath the water. The AIP System lessens this.
- The submarines’ noise levels are reduced as a result. The submarines are difficult to find as a result.
Types of Air Independent Propulsion System
Open-cycle systems
Submarines that use concentrated hydrogen peroxide as an oxygen supply beneath the ocean. They used steam turbines, which converted hydrogen peroxide into water vapour and oxygen in an atmosphere created by a potassium permanganate catalyst. Steam was heated by diesel fuel.
Closed-cycle diesel engines
The closed cycle diesel engine (CCD) uses a technology that enables the submarine to use its standard diesel engine on the surface and a different diesel engine for submerged conditions. For its subsurface activities, this specialized diesel engine used liquid oxygen combustion3. However, due to two distinct facts—maintaining the engine’s thermodynamic efficiency and disposing of exhaust against the water pressure at the dive’s depth—operating a diesel engine under submerged conditions would be a little difficult.
Closed-cycle steam turbines
Closed-cycle steam turbine technology uses an alternator and the turbine’s mechanical energy to generate electrical energy. It is based on the Rankine cycle. At a temperature above 600 °C, the system burns liquid oxygen (LOX) in addition to the ethanol that serves as its primary fuel. The steam circuit receives the heat created and uses it to power the turbine. The electrical power necessary for auxiliary circuits and propulsion machinery is generated by the alternator connected to the turbine.
Stirling cycle engines
Stirling engines produce energy by combining liquid oxygen with diesel fuel oil. The stirling cycle is the system’s foundation. The working fluid, which is permanently contained as a component of the system, serves as the energy source. Heat captured from the working fluid powers the engine. After that, the energy is either used to direct the submarine’s propelling burden or to recharge batteries.
Fuel cells
Fuel cells are becoming a highly desired technology and may someday serve as the AIP technologies’ standard bearer. The System operates under the fundamental tenet that hydrogen and oxygen molecules combine to produce electrical energy, with water serving as the system’s main waste product. The submarine’s water dispensing system can be used to discharge the waste water outboard. Due to its numerous different advantages, such as compactness, stealth, and exhaust dispensing, fuel cells are always being explored in both the commercial and military sectors. The use of fuel cells on submarines dates back to the early 1980s and is still advancing quickly now thanks only to the creativity and flexibility of growth in the sector.
Nuclear power
The term “air-independent propulsion” is typically used to describe methods of enhancing the performance of vessels that are traditionally propelled. On the other hand, the technical definition of AIP includes nuclear power as an extra source of electricity.
India’s Air Independent Propulsion System
- The Indian Navy is prepared to acquire an Air Independent Propulsion System that was designed locally. All Kalvari-Class Submarines would be equipped with India’s indigenous Air Independent propulsion technology, according to DRDO.
- It will add two weeks to the endurance of conventional submarines. The AIP from DRDO is a fuel cell-based AIP. Fuel cells use oxygen and hydrogen to generate electricity. The DRDO has tested the AIP’s land-based prototype successfully.
- The Indian navy will undoubtedly have a strategic advantage over the submarines of Pakistan and China thanks to its AIP-equipped submarines. AIP will be positioned between the crew quarters and engine space because it will be installed on a hull extension.
- AIP will be provided right away for India’s Next-Generation Project 75I, under which the Indian Navy plans to buy six diesel-powered submarines.
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DRDO’s Air Independent Propulsion Technology
The technology is being developed by the Naval Materials Research Laboratory (NMRL) of the DRDO. A phosphoric acid fuel cell serves as the structure of it. Because of this development in marine propulsion systems, many non-nuclear vessels can function without requiring atmospheric oxygen. You can accomplish this by surfacing or snorkeling. India uses an AIP fuel-based technology that is unique in that hydrogen is made aboard the ship. This solution is being successfully used with the assistance of business partners L&T and Thermax. Kalvari will be updated around 2023.
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