News Excerpt:

A massive Rs 60,000 crore contract to modernize the Indian Navy submarine fleet to build six stealth submarines equipped with Air Independent Propulsion (AIP) technology.

About Air Independent Propulsion (AIP) Technology

• Traditional diesel-electric submarines need to surface frequently to recharge their batteries, limiting their underwater endurance to only a few days. As battery technology advanced, the endurance of these submarines increased proportionally. 
  • This improvement was insufficient to extend their underwater capabilities beyond a week. 
• With the emergence of submarines, there was a problem finding satisfactory forms of propulsion underwater. 
• AIP is mostly implemented as an auxiliary source, with the traditional diesel engine handling surface propulsion. Most of these systems generate electricity, which in turn drives an electric motor for propulsion or recharges the boat’s batteries.
• AIP allows longer submergence than a conventionally propelled submarine.
  •  A typical conventional power plant provides 3 megawatts maximum, and an AIP source around 10 percent of that.
  •  A nuclear submarine’s propulsion plant is much greater than 20 megawatts.
• DRDO is using the fuel cells-based AIP System. It is unique as the hydrogen is generated onboard. 
• The plant was operated in endurance mode and max power mode as per the user requirements. The system is being developed by the Naval Materials Research Laboratory (NMRL) of DRDO. 

• • Fuel cell based AIP system:

• • • A fuel cell converts chemical energy into electricity using hydrogen (fuel) and oxygen (oxidizer), producing water and heat as by-products. 
    • It consists of two electrodes (anode and cathode) separated by an electrolyte. The reaction between the electrodes generates electric current, which charges batteries. Catalysts speed up the reactions.

• Key features of AIP system:

• It allows the submarines to stay for longer hours in water. 
• The submarines need to come to the surface of the water to charge their batteries. This is reduced by the AIP System.
• It decreases the noise levels made by the submarines. This makes it hard to detect the submarines.