Copyright 2001,2002 I. Urieli. This material is made available to SESUSA by Dr. Israel Urieli of Ohio University in Athens, OH. The text has been edited to facilitate its use by non resident students of the Stirling Engine who cannot attend classes in person. Please do not pester Dr. Urieli with questions regarding this site. He has a full teaching load plus several research projects. Please post all questions for discussing this site to the SESUSA knowledge exchange list server at sesusa@yahoogroups.com.

Stirling Engines - Mechanical Configurations

The mechanical configurations of Stirling engines are generally divided into three groups known as the Alpha, Beta, and Gamma arrangements. Alpha engines have two pistons in separate cylinders which are connected in series by a heater, regenerator and cooler. Both Beta and Gamma engines use displacer-piston arrangements, the Beta engine having both the displacer and the piston in an in-line cylinder system, whilst the Gamma engine uses separate cylinders.

The Alpha engine is conceptually the simplest Stirling engine configuration, however suffers from the disadvantage that both pistons need to have seals to contain the working gas. Andy Ross of Columbus, Ohio has been developing small air engines with extremely innovative Alpha designs, including the classical Ross-Yoke drive and more recently a balanced "Rocker-V" mechanism, as shown below.

The Alpha engine can also be compounded into a compact multiple cylinder configuration, enabling an extremely high specific power output, as is required of an automotive engine. A schematic diagram of this configuration is shown below. Notice that the four cylinders are interconnected, so that the expansion space of one cylinder is connected to the compression space of the adjacent cylinder via a series connected heater, regenerator and cooler. The pistons are typically driven by a swashplate, resulting in a pure sinusoidal reciprocating motion having a 90 degree phase difference between the adjacent pistons.

A modern design of this type is the STM 4-120 engine made by STM Power. A cutaway diagram of this engine is shown below. Refer to STM's website for further details of this engine.

On to Beta Engines, Gamma Engines

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