The Stirling engine is a heat engine that is vastly different from the internal-combustion engine in your car. Invented by Robert Stirling in 1816, the Stirling engine has the potential to be much more efficient than a gasoline or diesel engine. But today, Stirling engines are used only in some very specialized applications, like in submarines or auxiliary power generators for yachts, where quiet operation is important. Although there hasn’t been a successful mass-market application for the Stirling engine, some very high-power inventors are working on it.
A Stirling engine uses the Stirling cycle, which is unlike the cycles used in internal-combustion engines.
- The gasses used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and there are no explosions taking place. Because of this, Stirling engines are very quiet.
- The Stirling cycle uses an external heat source, which could be anything from gasoline to solar energy to the heat produced by decaying plants. No combustion takes place inside the cylinders of the 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.
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 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.