Editing Stirling engine (section)

=== Beta ===
[[file:Stirling Animation.gif|thumb|upright|Beta-type Stirling engine, with only one cylinder, hot at one end and cold at the other. A loose-fitting displacer shunts the air between the hot and cold ends of the cylinder. A power piston at the open end of the cylinder drives the flywheel]]

A beta Stirling has a single power piston arranged within the same cylinder on the same shaft as a [[#Displacer|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 between the hot and cold heat exchangers. 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, as the power piston is not in contact with the hot gas.<ref name="Keveney-2000b" />

# Power piston (dark grey) has compressed the gas, the displacer piston (light grey) has moved so that most of the gas is adjacent to the hot heat exchanger.
# The heated gas increases in pressure and pushes the power piston to the farthest limit of the power stroke.
# The displacer piston now moves, shunting the gas to the cold end of the cylinder.
# The cooled gas is now compressed by the flywheel momentum. This takes less energy, since its pressure drops when it is cooled.