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How Does a Stirling Engine Work

The Stirling Engine, developed by the Rev Robert Stirling in 1816, has a simple method of working although there are various designs that put this into practice. His reason for developing the engine was due to the accidents that had occurred with bursting boilers on steam engines, causing deaths or horrendous injuries.
His engine (which he called the air engine) however had not always been reliable and so didn't become widely used.
At the end of the 20th and into the 21st centuries, Robert Stirling's engine has found a new niche. As it can run from absolutely any source of heat that is applied externally, solar energy, particularly from light concentration, can be used with the engine driving a generator.


How does it work?

How a Stirling Engine Works
The single cylinder plus displacer Stirling Engine

The Stirling engine has a piston in a cylinder (similar to the internal combustion engine) driving a crankshaft, the movement of the piston being powered by a gas (possibly air) in a sealed chamber where part is heated and part is cooled, or has cooling fins. Within the chamber will be a mechanism, connected to the crankshaft, that will move the air alternately from the heated to the cooled portion of the chamber.
This will repeatedly heat and cool the gas causing it to expand and contract. This expansion and contraction powers the piston. This can be achieved without the use of valves.

Single Cylinder Sterling Engine
The single cylinder Stirling Engine with displacer
in the same cylinder

All that is required for the engine to run is that there should be a temperature difference between the hot and cold parts of the gas chamber. Models have been built that can run with just a 4oC temperature difference though commercial engines are likely to run on a few hundred degree differential. These engines have the potential to be the most efficient form of combustion engine.

Stirling engines and Solar Power

Diagramme of Stirling Engine mounted on a parabolic reflector

Stirling engines provide a neat method of converting heat energy to motion that can drive a generator.
The most common arrangement is to have the engine at the focus of a parabolic mirror. The mirror will be mounted on a tracking device to keep the suns rays focussed on the engine.