The Stirling engine is basically a heat engine that is vastly different from the internal-combustion engine. It was Invented by Robert Stirling in 1816, the Stirling engine has the potential to be much more efficient than a gasoline or diesel engine. A Stirling engine uses the Stirling cycle, which is unlike the cycles used in internal-combustion engines.
The engine is designed so that the working gas is generally compressed in the colder portion of the engine and expanded in the hotter portion resulting in a net conversion of heat into work. An internal Regenerative heat exchanger increases the Stirling engine's thermal efficiency compared to simpler hot air engines lacking this feature.
Here is a look at the three main types of Stirling Engine and their working.
Alpha Type Stirling Engine:
An alpha Stirling contains two power pistons in separate cylinders, one hot and one cold. The hot cylinder is situated inside the high temperature heat exchanger and the cold cylinder is situated inside the low temperature heat exchanger. This type of engine has a high power-to-volume ratio but has technical problems due to the usually high temperature of the hot piston and the durability of its seals. In practice, this piston usually carries a large insulating head to move the seals away from the hot zone at the expense of some additional dead space.
Beta Type Stirling Engine:
A beta Stirling has a single power piston arranged within the same cylinder on the same shaft as a displacer piston. The displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas from the hot heat exchanger to the cold heat exchanger. When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston. When it is pushed to the cold end of the cylinder it contracts and the momentum of the machine, usually enhanced by a flywheel, pushes the power piston the other way to compress the gas. Unlike the alpha type, the beta type avoids the technical problems of hot moving seals.
Gamma Type Stirling Engine:
The third type of Stirling engine is a gamma type sterling engine. Gamma type sterling engine can be called simply as a beta type sterling engine in which the power piston is placed in a separate cylinder alongside the displacer piston cylinder instead of the same, but is still connected to the same flywheel. The gas in the two cylinders can flow freely between both of them and remain as a single body. This configuration produces a lower compression ratio but it is mechanically simpler to the others and often used as a multi-cylinder Sterling engine.