How do diesel submarines work?

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Combustion engines need oxygen to combust! Where do submarines get their air when submerged?

In: Technology

Most diesel subs have two or more diesel engines. The diesels can run propellers or they can run generators that recharge a very large battery bank. They can also work in combination, one engine driving a propeller and the other driving a generator.

The sub must surface (or cruise just below the surface using a snorkel) to run the diesel engines. Once the batteries are fully charged, the sub can head underwater. The batteries power electric motors that drive the propellers. Battery operation is the only way a diesel sub can actually submerge.

The limits of battery technology severely constrain the amount of time a diesel sub can stay underwater. This is the huge benefit of using nuclear power in a sub. Nuclear generators need no oxygen, so a nuclear sub can stay underwater for weeks at a time.

Either they run with air from a snorkel, or they compress air when surfaced and carry it with them. Generally they run the engines to charge batteries and actually connect electric motors to the propellors. So unless you’re down for a long time, you don’t need to run the diesels constantly to power the ship.