The above video shows Stirling engine enthusiasts motoring around on the River Thames. This engine, invented in 1816 by Robert Sterling, consists of, at minimum, two pistons, one of which is heated. Karim Nice of How Stuff Works explains the cycle:
1. Heat is added to the gas inside the heated cylinder (left), causing pressure to build. This forces the piston to move down. This is the part of the Stirling cycle that does the work.
2. The left piston moves up while the right piston moves down. This pushes the hot gas into the cooled cylinder, which quickly cools the gas to the temperature of the cooling source, lowering its pressure. This makes it easier to compress the gas in the next part of the cycle.
3. The piston in the cooled cylinder (right) starts to compress the gas. Heat generated by this compression is removed by the cooling source.
4. The right piston moves up while the left piston moves down. This forces the gas into the heated cylinder, where it quickly heats up, building pressure, at which point the cycle repeats.
The Stirling engine never caught on as well as internal combustion engines did, but has in recent years caught the attention of solar energy developers.
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