Re: Will Stirling Engines on Submarines Work Forever?

The stirling engine is an external combustion engine that works by heating 
a gas in one section of the engine and cooling it in another, using the 
difference in volume of the gas when heated and cooled to drive a piston 
that provides the power.

Using the internal heat of a submarine to heat the gas and the ocean to 
cool it would not work because there would be no provision for replacing 
the heat extracted from the submarine and the submarine temperature would 
quickly approach that of the ocean,  to the point where the engine would 
not operate.

Even if it weren't for this basic problem, the difference in temperature in 
the submarine and the ocean would be variable depending on the location - 
the ocean could even be warmer - and in any case the difference would not 
be great enough to generate an appreciable amount of power. 

The Sweedish Gotland class submarines use a stirling engine that is driven 
by combustion of a hydrocarbon fuel.  The fuel is burned using oxygen 
stored on the submarine, so the combustion gas is water and carbon dioxide. 
 Some of the combustion gas is recycled to mix with more oxygen, and the 
remainder is discharged into the ocean.

For a description of the Gottland class submarine see: http://sesusa.hypermart.net/gotland.htm

For a description of the operation of a stirling engine, see: http://www.bekkoame.ne.jp/~khirata/english/still_a.htm