Work is apace at the Defence Research and Development Organisation's Naval Materials Research Laboratory at Ambernath in Maharashtra on developing a land-based prototype plug, and subsequently an engineered, operational version of an Air Independent Propulsion (AIP) system that will significantly cut the ‘indiscretion rate' of diesel and electric submarines.
The ‘indiscretion rate' is the percentage of time a submarine spends snorting when it is most vulnerable.
By eliminating the need for conventional submarines to frequently resurface for recharging batteries by breathing in air, it would considerably enhance their sub-surface endurance.
Talking to The Hindu here recently, J. Narayana Das, DRDO's Chief Controller, Research and Development (Naval Systems, Materials and Human Resources), said the Navy was satisfied with the DRDO's proposal. “We are first having a land-based demonstrator. And, as we progress, we will concurrently start an engineered version because engineering anything for a submarine platform is a completely different ballgame.”
(Incidentally, The Hindu has learnt from sources in the Navy that it has asked the DRDO to come up with a fully engineered fuel cell AIP by 2014 for possible use in the last two of the six Scorpene submarines being built in Mumbai's Mazagaon Dock. The Navy has also given sanction for the land-based prototype AIP in August this year.)
Asked about the recent offer of French defence major DCNS to install its MESMA AIP in the last two Scorpenes, Mr. Das said he wouldn't want to commit on the platform that would have the indigenous AIP fitted. “It depends on which platform will be ready and which will come in then.”
With the Navy
“We are working in tandem with the Navy as we don't have any other customer for the project. It will be ready in four to five years from now. The technology development is going on, and at an appropriate time, we will start marinisation and engineering for submarine quality. We are going to have industrial partners with us... Whatever we install will be on an operational submarine,” Mr. Das said.
Safety ensured
Explaining the technologies available for improving the sub-surface endurance of conventional submarines, he said the AIP being developed by the DRDO also ensured a higher level of safety to the submarine.
“In our technology, we generate hydrogen online on an as-needed basis. If you need more hydrogen when you are going fast, you produce more hydrogen and if you need less hydrogen, you produce less of it. The policy is ‘do not store hydrogen on board,' which ensures a higher level of safety to the platform. Also, we use fuel cells of a different type — phosphoric acid fuel cells — as they can tolerate slightly impure hydrogen. This is because when you produce hydrogen on board, you cannot have very pure hydrogen whereas other companies making fuel cell-based AIP are using PEM (proton exchange membrane) fuel cell, which necessitates hydrogen to be of ‘five-nines' quality, meaning 99.999 percent pure,” he said.
Hydrogen
“The AIP developed by the DCNS, on the contrary, worked on combustion of fuel using a steam turbine and producing electricity,” Mr. Das said. “Some other companies are using fuel cells themselves. They keep hydrogen stored on board. But if you want to be underwater for longer durations, you need larger quantities of hydrogen. Oxygen is required, but both systems use oxygen which is stored as [cryogenic] liquid oxygen…. And when you talk of a submarine's power system, the hydrogen you need is in the order of a couple of tonnes. Further, it has to be carried either in metal hydrides or in compressed cylinders. But high-pressure hydrogen is a potential explosive hazard.”
