Indian Navy Sticks with DRDO Developed AIP, for Better or Worse!

Scorpene cutaway scale model with DCNS AIP plug at DefExpo 2014

The Business Standard reported on July 20, 2015 that because of delay in DRDO's Air Independent Propulsion (AIP) project, which is almost 4 yr behind schedule, only the sixth Project-75 Scorpene would be fitted with an AIP plug. It is also possible that all six Scorpenes would be built without AIP.

The Indian Navy had earlier asked Mazagon Docks Limited (MDL) to equip the fifth and sixth boats with AIP by fitting an additional 300-t section on the last two Scorpene submarines built at MDL under Project 75.

MDL and French firm DCNS, which developed the Scorpene, are responsible for fitting the new hull section and safely integrating the DRDO-developed AIP plug to the submarine.

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.

The Navy's penchant for sourcing its systems from within India is well appreciated in the country, but there can be no denying the risk that the Navy is taking by adding to its fleet, in this day and age, new submarines without AIP! India's adversaries, China and Pakistan, have been operating AIP subs for years now!

The following comparison may help readers assess the risk for themselves. Please feel free to your your views through the comments section.

DCNS and DRDO AIPs Compared

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.

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. But then DRDO has a well earned notoriety of delays!