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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). AIP can augment or replace the diesel-electric propulsion system of non-nuclear vessels.
Here is a comparison of DCNS's Closed Cycle Steam Turbine MESMA AIP vs DRDO's Fuel Cell AIP System For IN's Kalvari-class SSK's -
DCNS MESMA AIP
The MESMA AIP from DCNS mimcs nuclear propulsion. It uses heat generated through combustion of ethanol (grain alcohol) and stored oxygen at a pressure of 60 atmospheres to power a conventional steam turbine power plant. It doesn't use fuel cells.
The DRDO AIP uses fuel cell technology. A fuel cell converts chemical energy from a fuel into electricity through a chemical reaction of positively charged hydrogen ions with oxygen or another oxidizing agent.
There are many fuel cell types, but the principal ones include the alkaline fuel cell (AFC), proton exchange membrane (PEM) fuel cell, direct methanol fuel cell (DMFC), molten carbonate fuel cell (MCFC), phosphoric acid fuel cell (PAFC), and solid oxide fuel cell (SOFC).
DRDO's AIP uses PAFC, which has some advantages over other fuel cell types. PAFCs offer a broader choice of fuel being more tolerant of fuel impurities. It can operate using reformed hydrocarbon fuels (Methanol) or biogas.
PAFC operating temperatures (150 to 200 °C) are higher and as a result they generate steam as byproduct, besides electric power for propulsion. The steam can be used to meet other heating requirements, pushing up operating efficiency to as high as 70%.
PAFC fuel cells were one of the earliest to be developed and are commercially available of the shelf (COTS).
The only downside of PAFCs is the use of phosphoric acid as electrolyte. However, use of modern materials makes PAFC safe enough for commercial use at hospitals, schools, office buildings, and grocery stores.
It's likely that the DRDO plug uses commercially available PAFCs.
The second generation fuel-cell AIP developed by DCNS usees hydrogen produced from diesel fuel by hydrocarbon reforming.
One obvious advantage of the DCNS AIP is the easy availability of diesel at any port around the globe. The absence of pure-oxygen in the cells allows longer life cycle. DCNS claims that the life cycle of its new AIP plug roughly matches the life-cycle of the submarine, which isn't the case with other fuel cell types.
For DCNS MESMA the hazards (like DRDO Fuel cells) of storing and handling the liquid oxygen (LOX). While the MESMA may provide higher power output, its net efficiency might be the lowest (estimated at. 25%) as its rate of oxygen consumption is higher. The MESMA has significant moving parts, which may radiate detectable noise. Ultimately, the maintenance and crew training requirements of the MESMA steam turbine system are significant - adding to cost. The burning process yields exhaust carbon dioxide which needs to be expelled behind the sub at any depth perhaps making it vulnerable to advanced airborne and ASW ship sniffing sensors.
Though relatively high output power is available and the design permits relatively easy retrofitting into existing submarines by adding an extra hull section-plug. There is no doubting the sophistication of the DCNS 2nd generation AIP, which has to be weighed against the higher initial cost, high recurring cost from the need to use AIP is all future conventional subs, and the continued dependence on foreign technology.
Additional Note(s):-
>> Two of PN's Agosta 90B Submarines are fitted with DCNS MESMA AIP.
>> PLAN's Type 041 (Yuan class) submarines and Type 032 (Qing class) submarines are fitted with Sweden's Saab Stirling AIP.
>> DRDO Fuel Cell AIP has an endurance of 25 days against 28 days of DCNS MESMA AIP System.
>> Last two of the Kalvari-class SSK's are to be fitted with DRDO Fuel Cell AIP.
>> DCNS initially offered its first generation MESMA AIP with the Scorpene, but the Indian Navy opted to go with a second generation DRDO developed 300-t AIP based on fuel cell technology. DCNS has since developed and demonstrated to Indian journalists a fully tested second generation operational-scale fuel cell AIP that would allow the Scorpene to stay submerged for 3 weeks, but the Indian Navy hasn't been swayed from its decision to go with the DRDO AIP. (Without AIP, Scorpene can stay submerged for 4 days. With a MESMA AIP, it would be able to stay submerged for 2 weeks.)
>> DRDO has demonstrated its AIP technology on a land based prototype. Trials on a land based submarine section were to commence from March 2015 and full scale operations of a AIP System was to be demonstrated within 2015.
>> One good reason why the Navy has stuck with the DRDO AIP is because it could later be reconfigured for the submarines to be acquired under Project 75I. Also, the four Scorpenes launched earlier could be retrofitted under an upgrade program.
Here is a comparison of DCNS's Closed Cycle Steam Turbine MESMA AIP vs DRDO's Fuel Cell AIP System For IN's Kalvari-class SSK's -
DCNS MESMA AIP
The MESMA AIP from DCNS mimcs nuclear propulsion. It uses heat generated through combustion of ethanol (grain alcohol) and stored oxygen at a pressure of 60 atmospheres to power a conventional steam turbine power plant. It doesn't use fuel cells.
There are many fuel cell types, but the principal ones include the alkaline fuel cell (AFC), proton exchange membrane (PEM) fuel cell, direct methanol fuel cell (DMFC), molten carbonate fuel cell (MCFC), phosphoric acid fuel cell (PAFC), and solid oxide fuel cell (SOFC).
DRDO's AIP uses PAFC, which has some advantages over other fuel cell types. PAFCs offer a broader choice of fuel being more tolerant of fuel impurities. It can operate using reformed hydrocarbon fuels (Methanol) or biogas.
PAFC operating temperatures (150 to 200 °C) are higher and as a result they generate steam as byproduct, besides electric power for propulsion. The steam can be used to meet other heating requirements, pushing up operating efficiency to as high as 70%.
PAFC fuel cells were one of the earliest to be developed and are commercially available of the shelf (COTS).
The only downside of PAFCs is the use of phosphoric acid as electrolyte. However, use of modern materials makes PAFC safe enough for commercial use at hospitals, schools, office buildings, and grocery stores.
It's likely that the DRDO plug uses commercially available PAFCs.
The second generation fuel-cell AIP developed by DCNS usees hydrogen produced from diesel fuel by hydrocarbon reforming.
One obvious advantage of the DCNS AIP is the easy availability of diesel at any port around the globe. The absence of pure-oxygen in the cells allows longer life cycle. DCNS claims that the life cycle of its new AIP plug roughly matches the life-cycle of the submarine, which isn't the case with other fuel cell types.
For DCNS MESMA the hazards (like DRDO Fuel cells) of storing and handling the liquid oxygen (LOX). While the MESMA may provide higher power output, its net efficiency might be the lowest (estimated at. 25%) as its rate of oxygen consumption is higher. The MESMA has significant moving parts, which may radiate detectable noise. Ultimately, the maintenance and crew training requirements of the MESMA steam turbine system are significant - adding to cost. The burning process yields exhaust carbon dioxide which needs to be expelled behind the sub at any depth perhaps making it vulnerable to advanced airborne and ASW ship sniffing sensors.
Though relatively high output power is available and the design permits relatively easy retrofitting into existing submarines by adding an extra hull section-plug. There is no doubting the sophistication of the DCNS 2nd generation AIP, which has to be weighed against the higher initial cost, high recurring cost from the need to use AIP is all future conventional subs, and the continued dependence on foreign technology.
Additional Note(s):-
>> Two of PN's Agosta 90B Submarines are fitted with DCNS MESMA AIP.
>> PLAN's Type 041 (Yuan class) submarines and Type 032 (Qing class) submarines are fitted with Sweden's Saab Stirling AIP.
>> DRDO Fuel Cell AIP has an endurance of 25 days against 28 days of DCNS MESMA AIP System.
>> Last two of the Kalvari-class SSK's are to be fitted with DRDO Fuel Cell AIP.
>> DCNS initially offered its first generation MESMA AIP with the Scorpene, but the Indian Navy opted to go with a second generation DRDO developed 300-t AIP based on fuel cell technology. DCNS has since developed and demonstrated to Indian journalists a fully tested second generation operational-scale fuel cell AIP that would allow the Scorpene to stay submerged for 3 weeks, but the Indian Navy hasn't been swayed from its decision to go with the DRDO AIP. (Without AIP, Scorpene can stay submerged for 4 days. With a MESMA AIP, it would be able to stay submerged for 2 weeks.)
>> DRDO has demonstrated its AIP technology on a land based prototype. Trials on a land based submarine section were to commence from March 2015 and full scale operations of a AIP System was to be demonstrated within 2015.
>> One good reason why the Navy has stuck with the DRDO AIP is because it could later be reconfigured for the submarines to be acquired under Project 75I. Also, the four Scorpenes launched earlier could be retrofitted under an upgrade program.
