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The Stirling motor as the drive for submarines
Since its invention by the Scottish clergyman Robert Stirling in 1815, the Stirling motor has been developed continuously over time and is now used in many different fields of application. For example, Stirling motors are used in the field of solar power generation, space travel, or as cooling units in thermal imaging cameras. In addition, there are plans to make use of Stirling motors as water pumps in the Third World. They are also used as the drive for submarines.
From the outset, engineers searched for suitable ways to extend submarine diving times. In the past, nuclear submarines alone led in this field. With the use of aStirling motor as a non-nuclear, conventional drive, however, this has changed. A Stirling motor, an air independent propulsion system, greatly increases the underwater range of a non-nuclear submarine. It was thereby possible to increase the duration of an underwater journey from a few days to a few weeks. Until then, that was only possible for nuclear submarines. Along with the significant extension of diving times, the risk of being located is decreased. In addition to this increased underwater range, using a Stirling motor to drive a submarine offers other advantages. This type of motor is vibration-free and extremely quiet. This makes locating the boat even more difficult. Moreover, submarines operated with a Stirling motor feature considerably better maneuverability than their nuclear-driven counterparts. These characteristics pay for themselves, particularly in operations in coastal waters. Even on the open sea, however, submarines equipped with external-air-independent Stirling motors have long since proven themselves.
In view of the beneficial properties of Stirling motors for propelling submarines, the Ministry of Defense granted MAN Technologie AG the order to develop a 12-cylinder submarine motor with helium as the working gas. Partly due to a world political situation which was becoming less tense, however, work on this project was discontinued in the late 1980s.
Already in 1998, the Swedish Navy started using Stirling motors to drive their non-nuclear submarines of the Gotland class, which had replaced the older Västergötland class. These submarines were the first in the world equipped with a Stirling motor as the drive. The air independent propulsion system was developed and implemented by a Swedish company, Kockums, based in Malmö, and then prepared for serial production by ThyssenKrupp Marine Systems. Today, all submarines of the Swedish Navy are equipped with this type of Stirling drive system which has a capacity of approximately 75 kW. There is also the possibility of upgrading older submarines with this type of power source.