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The Manson engine is a hot air engine that was first described by A. D. Manson in the March 1952 issue of Newnes Practical Mechanics-Magazines.[1] Manson engines can be started in either direction (clockwise or anti-clockwise).[2] It has a stepped piston. The front part acts as a displacer and the back part acts as a work piston (the displacer and the work piston move as a single component).[3][1] The engine only requires three moving parts: piston,[3] piston rod, and crank.
The engine is double acting,[1] using both the expansion of the warmed air and atmospheric pressure overcoming the reducing pressure of the cooling air to do work.[3][4][5]
The engine currently has no commercial or practical applications. The engines are built mainly as desk toys, physics demonstrations, and novelties.[2]
Stirling engines are typically closed systems, while Manson engines are open systems.[3][5][8][2] The displacer and work piston of the Manson engine have zero phase angle.[4]
The valves and gas paths are considered by some to be complicated to manufacture, so various variants exist with improved, modified, or simplified valves and gas paths.[9][10]