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Air Engines: The History, Science, and Reality of the Perfect Engine
Theodor Finkelstein
Theodor Finkelstein
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Allan J. Organ
Allan J. Organ
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ASME Press
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Between the two world wars little use was made of air engines other than for trivial applications, such as scientific toys, or for very small engines for special purposes, such as liquid stirrers in laboratories or powered fans for the Far East. Although many older engineers still affectionately remember small air engines as the first mechanical toy they ever played with as boys, the working principle was nearly forgotten, until even textbooks on thermodynamics included little more than a brief reference.

This subject was reopened a few years before the last world war at the Physical Research Laboratories at Eindhoven, then under the direction of Professor G. Holst. Tests showed that the overall thermal efficiency of air engines available at the time amounted to less than 1 per cent, compared with a figure indicated by the theory underlying the Carnot cycle, which may be up to 50 times as great. It is reported that this enormous difference between actual and theoretical performance caused Professor Holst to embark on this research, which was undertaken by a large team of scientists working under H. Rinia and continued partly in secret during the war under German occupation. Some leakage of information occurred, however, and towards the end of the war a German ‘Spreng Kommando’ was called in to remove a novel type of secret engine that was being developed. This they did, including some cylinders believed to contain a new secret fuel, which, on closer inspection, turned out to be nothing but compressed Dutch air (Anon. 1947).

In the course of this research work the fundamental properties of Stirling engines in general were investigated. For this purpose a number of different experimental models were built, some using the Rider construction with two loaded pistons, others the Stirling single-cylinder principle with one piston and one displacer. When the war ended, a number of successful small prototypes had been produced with quite startling performance compared with the old-type air engines (Rinia and duPré 1946). It was claimed that for equal powers the swept volume had been reduced by a factor of 125 and the weight by a factor of 50, comparison being made with a model still in production in 1923 (deBrey et al. 1947). Yet the general principle, as well as the layout of these single-cylinder engines hardly differed from Stirling's original engine of 1816, as can be seen from Fig. 4.1, which is a simplified section through the engine referred to. The photograph in Fig. 4.2 shows the external appearance.

4.1 The rediscovery
4.2 Double-acting types
4.3 Future possibilities
4.4 Acknowledgements to the original four articles
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