Philips Cryogenic Stirling Cycle Machine.

Type 95 -I5 piston/displacer style Cryogenerator, converted to engine form.
Engine No. NR 2086, Piston; 80mm x 50mm. Displacer: 70mm (now 98mm) x 27mm.
Working gas; originally H2 or He at 40 bar, now in engine form; air at 15bar.

From popularity in some niche markets during the 19th century Stirling cycle engines lost out in the rise of the internal combustion engine during the early 20th.
In the late 1930's, Philips (Netherlands) were on the lookout for a small, quiet, economical generator to run vacuum tube radios at off-grid locations.
They considered many options; internal combustion engines, steam engines, thermo-couple chimneys and others but eventually chose Stirling cycle engines because their analysis indicated that with rigorous scientific design and the use of new materials capable of operating at high temperatures, they could best serve the requirements.
By 1940 they had produced prototype engines with much higher specific output (power for size) and more than twice the efficiency of any previous Stirling cycle engine.
Development continued in secret during the 1940 to 1944 German occupation.
By 1952, a pre-production batch of their 102C 700watt generator had been completed- just as transistors replaced vacuum tubes in radios, and their original need disappeared.
However, the Stirling cycle is reversible and theoretically the most efficient there can be, so Stirling cycle heat pumps (basically Stirling engines driven by electric motors) can generate very low temperatures. From 1948, Philips set up a division under JWL Kohler to develop Stirling cycle based units for this purpose and from 1954, began selling liquid air cryogenerators to universities and research laboratories. They later developed micro units for cooling infrared sensors and much larger cryogenerators to reach the very low temperatures required for super conductivity.
This is an original 1950's Philips liquid air machine, ex Waikato University. While theoretically capable of functioning as an engine in original form, its volume ratios were not ideal for this and the original heater head was incapable of accepting combustion temperatures. To get it to run satisfactorily as an engine, a new heater, head, cooler and displacer were fitted. The original piston and cylinder were not changed. Replaced parts (including the snow separator) have been retained so that it may someday be restored to original cryogenerator form.
Philips went on to develop Stirling cycle engines for many uses; ships, cars, satellites and etc. Their licensees during the 1950 to 1990 period included Ford, GM, DAF, MAN, NASA and many others. None of these developments resulted in successful commercial products, except maybe for submarines, but this application is still secret.
However, their cryogenerator division (sold in 1990) was very successful and is believed to have returned sufficient to cover all their Stirling engine research. This research has formed a solid base for the many Stirling engine development projects that are underway in the early 21st century, particularly for Stirling engine based solar farms and combined heat and power (CHP) makers such as Whispertech in Christchurch.

Peter Lynn, Ashburton, New Zealand, July '07

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