Is this a product of India-France collaboration?
If NO, Than I am just interested in the tests conducted before granting operational status. Thanks
No this is a stand alone effort by India. DRDO's NMRL and 2 indian private companies L&T and Thermax were involved
Thank you both, but I was looking for some Technical details.
in March 2021 The (AIP) plant was operated in endurance mode and maximum power mode as per the user requirements and completed its land-based trials at NMRL Lab Ambernath. As per reports, NMRL was able to demonstrate AIP operation for the endurance of 14 days under simulated underwater condition.
“The AIP would be fitted on the Kalvari class submarines during their 1st major refit after a standard certification from The Naval Group.
NMRL believes that its Phosphoric Acid Fuel Cell (PAFC) based AIP system is advanced than People’s Liberation Army Navy's current Stirling cycle based AIP (which they got from Sweden).
MESMA AIP module which is fitted in Pakistani Navy operated two French-designed Agosta 90B Class Submarines are relatively noisy and thus less stealthy when compared to Fuel Cell-based AIP system like the one DRDO has developed due to the presence of a large number of moving parts.
The longest Record is set by a Type 212A German Submarine using a Siemens proton exchange membrane (PEM) compressed hydrogen fuel cells based Air-independent propulsion (AIP) system for 18 days and If DRDO has achieved 14 days endurance with its Phosphoric acid fuel cell (PAFC) based Air-independent propulsion (AIP) system then we are par with Global leaders in AIP System.
Moreover, NMRL’s modular architecture scores over a composite system, since even if one of the modules fails, the control system for the PAFC stacks can reconfigure the remaining operational units to continue to supply power output, albeit at a reduced quantum. This naturally increases the survivability of the system, which is of utmost importance when being used to propel a submarine stealthily.
As of right now the technology has been transferred to Thermax Ltd in Pune for further production.
A conventional submarine’s diesel engine generates electricity which can be used to drive the propeller and power its systems. The problem is that such a combustion engine is inherently quite noisy and runs on air—a commodity in limited supply on an underwater vehicle. As battery technology improved, the endurance of these submarines increased proportionally. But it was not enough to last them beyond a week. Traditional diesel-electric submarines need to surface frequently to charge their batteries and have an underwater endurance of only a few days. This is done by snorkeling (coming on the surface to fill their oxygen tanks) , which 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 snorkeling. Modern surface, airborne and satellite sensors have become so sensitive that they can readily track surface wakes, acoustic and thermal signatures caused by snorkels, diesel engines and their exhausts. A submarine which needs to surface frequently, loses its element of surprise and increases its vulnerability to hostile anti-submarine assets.
IN CONTRAST TO THIS
nuclear-powered submarines are quieter, don’t consume air, and produce greater power output, allowing nuclear submarines to remain submerged for months instead of days while traveling at higher speeds under water. Nuclear-powered submarines have traditionally held a decisive edge in endurance, stealth and speed over cheaper diesel submarines.
However, new Air Independent Propulsion (AIP) technology has significantly narrowed the performance gap while only costing a fraction of the price of a nuclear-powered boat. AIP powered submarines have generally cost between $200 and $600 million, meaning a country could easily buy three or four medium-sized AIP submarines instead of one nuclear attack submarine.
Air-independent propulsion (AIP) is any marine propulsion technology that allows a non-nuclear submarine to operate without access to atmospheric oxygen (by surfacing or using a snorkel) thereby vastly improving their underwater endurance. AIP can augment or replace the diesel-electric propulsion system of non-nuclear vessels. AIP systems permit diesel-electric submarines to recharge their batteries independently of their engines.
Submarine designers and Navy submariners use an indiscretion ratio to indicate the proportion of mission time a submarine is detectable while charging its batteries. For conventional modern submarines the indiscretion ratio ranges typically 7-10% on patrol at 4 knots, and 20-30% in transit at 8-10 knots. This is where Air Independent Propulsion (AIP) comes in. It offers the possibility of increasing underwater endurance by a factor of up to three or four, which reduces the indiscretion ratio significantly.
AIP has a force multiplier effect on lethality of a diesel electric submarine as it enhances the submerged endurance of the boat, several folds. The hydraulics in a nuclear reactor produce noise as they pump coolant liquid, while an AIP’s submarine’s engines are virtually silent. AIP systems have been in high demand due to their increasing advantages in performing stealth underwater operations.
The advantage offered by increased underwater endurance can be used for ‘ambushing’ an approaching fleet. In one such scenario, an AIP equipped submarine can roam near a strait, waiting 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.
In another scenario, an AIP equipped sub can roam near enemy territory for far longer compared to a non-AIP sub and thus allow them to perform longer intelligence gathering and spy missions,
However, speed and longer range remains an undisputed strength of nuclear-powered submarines. U.S. attack submarine are able to sustain speeds of more than 35 miles per hour while submerged. By comparison, the German Type 214’s maximum submerged speed of 23 miles per hour is typical of AIP submarines. Current AIP technology doesn’t produce enough power for higher speeds, and thus most AIP submarines also come with noisy diesel engines as backup.
diesel electric submarines and by extension AIP based submarines possess the distinct advantage of being able to switch off their engines completely and silently wait unlike nuclear submarines whose rectors cannot be switched off at will.
AIP also has downsides, Installing AIP increases length and weight of submarines; requires pressurized liquid oxygen (LOX) storage on-board and supply for all three technologies, some AIP Technologies like MESMA and the Stirling engine have acoustic noise due to their moving parts. AIO also increases production cost by atleast 10%.
Although nuclear submarines offer far better range nd speeds, they are unsuitable for the shallow littoral waters and most navies cannot afford to build and maintain them as they are very expensive
AIP boats can be considered as something in-between conventional and nuclear submarines.
AIP configurations found in diesel-electric submarines
1. Closed Cycle Diesel Engines
This technology involves storing a supply of oxygen in the submarine in order to run a diesel engine while submerged. 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.
The main challenge with this technology is the storing of liquid oxygen safely on board the submarines. The Soviet subs which used this technology during the 1960s were found to be highly prone to fires and were subsequently discontinued their usage. Closed Cycle Diesel AIP is hence not preferred for modern submarines even though it is comparatively cheaper and simplifies logistics by the use of standard diesel fuel.
2. Closed Cycle Steam Turbines
Steam turbines make use of a source of energy to heat water and convert it into steam in order to to spin a turbine and generate electricity. 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 (Module d’Energie Sous-Marine Autonome / Autonomous Submarine Energy Module ) is the only such system available and it makes use of ethanol and oxygen as energy sources. The combustion of ethanol and oxygen under high pressure is used to generate steam. The steam generated is the working fluid and is used to run the turbine.
The first full-scale undersea application of the MESMA was in Pakistan’s three new Agosta 90B submarines, which are each be fitted with a 200 kilowatt MESMA system for increasing submerged endurance by a factor of three to five at a speed of 4 knots. Once again, the boat has to lug around ethanol and volatile liquid oxygen as well as complex machinery which produces noise but also a lot of power, which is good for high-speed operations.
3. Stirling Cycle
A Sterling Engine is a closed cycle engine with a working fluid which is permanently contained in the system. A source of energy is used to heat this 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. 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.
This is slightly more efficient, and somewhat less complicated, than the French MESMA and is used on Japanese (soryu class), Swedish (Gotland and Västergötland class) and Chinese (Yuan class) submarines.
The advantage of using Sterling engines is the easy availability of diesel fuel and low refueling costs when compared with Fuel Cells. They are also quieter than MESMA
The Stirling-cycle engine forms the basis of the first AIP system to enter naval service in recent times however They are bulky when compared to Fuel Cells. Although the technology is well proven and affordable, it also requires the boat to lug around liquid oxygen oxidizer, which has its own dangers,
The main drawback is that they are quite noisy when compared to Fuel Cells due to the presence of a large number of moving parts (even more than MESMA) . Also The operating depth of a submarine using Sterling AIP is limited to 200 m when AIP is engaged.
4. Fuel Cell
Fuel-cell technology is currently the state of the art in AIP. 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 (fuel) and Oxygen (oxidizer) into electricity, with water and heat released as by-products. This is done by an electrolytic cell which consists of a cathode and anode separated by an electrolytic barrier. The reaction produces an electric current, which is used to charge the batteries. A chemical catalyst is used to speed up the reactions.
A fuel cell has almost no moving parts which significantly reduces the acoustic signature of the sub. Fuel Cells can achieve an efficiency of over 80% under certain circumstances. They can also be scaled easily into large or small sizes depending on the displacement of the submarine. This is easier than developing different systems for each submarine class.
Since Fuel Cells generate no exhaust fumes, it eliminates the need to have special exhaust scrubbing and disposal machinery making the sub more stealthy. The only drawback of fuel cell based AIP is that they are expensive and complex. They are also not capable of quickly ramping-up its power output like say a MESMA configuration can.
Phosphoric Acid Fuel Cells (PAFC) and Proton Exchange Membrane Fuel Cells (PEMFC) are presently used in submarines. Germany is said to be the world leader in developing and fielding fuel cell based AIP, which is backed by the large number of export orders they have received. France is also developing a next generation Fuel Cell AIP as a successor to its MESMA. India is another country which is developing a Fuel Cell AIP to integrate on their submarines.
There are several alternative configurations of fuel cells, but for submarine propulsion, the so-called “Polymer Electrolyte Membrane” (PEM) fuel cells have attracted the most attention because of their low operating temperatures (80°C) and relatively little wasted heat. In a PEM device, pressurized hydrogen gas (H2) enters the cell on the anode side, where a platinum catalyst decomposes each pair of molecules into four H+ ions and four free electrons. The electrons depart the anode into the external circuit – the load – as an electric current. Meanwhile, on the cathode side, each oxygen molecule (O2) is catalytically dissociated into separate atoms, using the electrons flowing back from the external circuit to complete their outer electron “shells.”
The polymer membrane that separates anode and cathode is impervious to electrons, but allows the positively-charged H+ ions to migrate through the cell toward the negatively charged cathode, where they combine with the oxygen atoms to form water. Thus, the overall reaction can be represented as 2H² + O² => 2H²O, and a major advantage of the fuel-cell approach is that the only “exhaust” product is pure water. Since a single fuel cell generates only about 0.7 volts DC (direct current), groups of cells are “stacked” together in series to produce a larger and more useful output. The stacks can also be arrayed in parallel to increase the amount of current available.
German-built submarines have successfully taken advantage of fuel cell technology, and the French, Russians and Indians are also moving in this direction. It is thought that Australia’s upcoming Shortfin Barracuda class submarines, of French origin, will use fuel cell AIP propulsion. These massive submarines will offer as close to nuclear propulsion capabilities as possible. Israel’s latest Dolphin class boats of German origin also use fuel cell AIP
The S-80 is a new generation of submarines in production for the Spanish Navy by the national company Navantia will also use a fuel cell based AIP. A total of 4 S-80 have been ordered by the Spanish Navy.
All sensors and weapons being equal, a Navy has to justify what type of diesel electric submarine to choose based not just on cost but also on what type of tactics they aim to employ and what type of combat environment they are most likely to fight in. For instance, if long-range patrols and ambush tactics are common, along with the need for maximum stealth, fuel cell AIP technology may be best. If bursts of high-speed during attack and evasion maneuvers are needed often, along with high endurance, MESMA may be most appropriate. For shorter-range littoral combat operations, the Stirling Engine-based AIP technology may make the most sense.