The Beta configuration is the classic Stirling engine configuration and has enjoyed popularity from its inception until today. Stirling's original engine from his patent drawing of 1816 shows a Beta arrangement. A photograph of Robert Stirling, the original patent drawing, as well as an animated model of Stirling's engine is clearly shown in an interesting website by Bob Sier. Another important early Beta engine is Lehmann's machine on which Gusav Schmidt did the first reasonable analysis of Stirling engines in 1871. Andy Ross has recently built a small working replica of the Lehmann machine, as well as a model air engine, both based on single cylinder Beta configuration as shown below.
From the figure we see that unlike the Alpha machine, the Beta engine has a single power piston and a displacer, whose purpose is to "displace" the working gas at constant volume, and shuttle it between the expansion and the compression spaces through the series arrangement cooler, regenerator, and heater. Matt Keveney has done an excellent animation of a single cylinder Beta engine, showing clearly the principle of operation.
Rolf Meijer of Philips, Holland, derived his famous vibrationless rhombic drive Beta engines in the early 1960s.
Probably the most ingenious Stirling engines yet devised are the free-piston engines invented and developed by William Beale at Ohio University in the late 1960s. He later formed the company Sunpower, Inc., which has been the leader in the development of free-piston Stirling engines and cryocoolers to this day. All of Sunpower's engines are Beta arrangements and employ no mechanical linkage system. The main aspect of the free piston machine is that the output power can be obtained through a linear alternator, allowing the entire system to be hermatically sealed. Sunpower have recently begun to manufacture Stirling cycle croygenic coolers for liquifying oxygen. Over the years Sunpower has transformed Athens, Ohio into a hotbed of Stirling cycle machine activity, which now includes three R&D and manufacturing companies as well as one internationally recognized consultant in the area of Stirling cycle computer analysis.
Stirling Technology Inc. is a spinoff of Sunpower, and was formed in order to continue the development and manufacture of the 5 kW ST-5 Air engine. This large Beta type engine burns biomass fuel (such as sawdust pellets or rice husks) and can function as a cogeneration unit in rural areas. It is not a free-piston engine, and uses a bell crank mechanism to obtain the correct displacer phasing.
Global Cooling is a licencee of Sunpower, mainly in order to develop free-piston Stirling cycle coolers for home refrigerator applications. These systems, apart from being significantly more efficient than regular vapor-compression refrigerators, have the addad advantage of being compact, portable units using helium as the working fluid (and not the Ozone destroying CFCs).
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