Stirling Cycle Engine, LTD Displacer Gamma Type

Invented by Scottish inventor Robert Stirling in 1816, the Stirling Cycle Engine is a practical 'external combustion' engine that transforms any heat source to mechanical energy. It is one of the most efficient mechanical methods of doing this. While it has been useful in niche applications for many decades, and remains so today, it is not as widely known as internal combustion engines and other kinds of external combustion engines, such as steam engines. It is best when running continuously in applications where the exact speed is not critical, and where rapid changes in its speed are not required. Because of this is has not found use so far in automobiles, but with the return of electric cars, it my find some application as a way to generate the electric power needed by the cars. Otherwise, it has traditionally found use for pumping water, for remote electrical generation, as well as other situations.

All Stirling Cycle engines use an enclosed fluid, usually air, that simply moves back and forth in the engine. Most types use two cylinders, one whose job is primarily to do the 'work', and the other whose job is to help move the fluid back and forth in the engine. All Stirling Cycle engines
use the difference in temperatures between two parts of the engine as their source of energy .

The LTD (Low Temperature Differential) Gamma type engine shown here uses two cylinders, moving the fluid back and forth between them. With this 'Displacer' variant, a large area piston, called the Displacer, moves between two plates, one warm and the other relatively cooler. The displacer does not fit tightly inside the cylinder, because it simply needs to encourage the fluid to move, but also needs to allow the fluid to flow around the piston, bypassing it. The much smaller 'power' piston is the one that actually does the work. The speed of the engine is controlled by the difference in the two temperatures. The displacer type engine, because of its large surface area, can work well with much less heat than most other types of Stirling engine. The one shown in this video is capable of running slowly from just the heat of a human hand holding the bottom metal plate. But in this
video, to get a faster speed, the bottom plate rests on a cup that is partially filled with warm water. Notice that the engine starts running very slowly because the water has not yet warmed the bottom plate very much. But once the plate warms up, the engine speed picks up significantly.

The engine in this video is machined from aluminum, with acrylic displacer cylinder walls and the displacer piston is a simple disk of stiff foam insulation. It was obtained from Sci-Supply.com, and is a ready-to-go engine that does not require assembly (only the large flywheel needs to be mounted to the axle).

Wikipedia and HowStuffWorks have good descriptions of exactly how Stirling Cycle engines work.

Category:

Science & Technology

Tags:

• Stirling cycle
• Sterling cycle
• external combustion