Philips 95 –I5 Stirling engine conversion

Philips 95 –I5 Stirling engine conversion.

Engine No. NR 2086 beta type cryocooler, converted to engine form.

Piston; 80mm.  Displacer: 98mm (originally 70mm). 

 Working fluid; air at 15 bar (originally Hydrogen or Helium at 40 bar).

The Stirling thermodynamic cycle is reversable.  When there is a sufficient temperature difference between an engine’s hot and cold heat exchangers it produces mechanical power.  When, instead, it’s rotated by an external power source (an electric motor for example) a temperature difference is created between the two heat exchange surfaces.  Because the Stirling cycle is a theoretically perfect thermodynamic cycle (what’s called Carnot efficiency) it can be used to achieve very low temperatures.

This is an original 1950’s Philips cryocooler used to liquify air (ex-Waikato University) and has been converted to run as an engine.   In original form, volume ratios were not ideal for this and nor was the original heater head capable of accepting combustion temperatures.  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 are in storage.

Philips Stirling cycle history: In the late 1930’s, Philips (Netherlands) wanted a small, quiet, efficient generator to run vacuum tube radios at off-grid locations.  They considered many options; internal combustion engines, steam engines, and thermo-couple chimneys, but concluded that with scientific design and the use of new materials capable of operating at high temperatures, a Stirling engine generator would best meet their criteria.

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 engine. Development continued in secret during the 1940 to 1944 German occupation.

By 1952, a pre-production batch of their 102C 300-watt generator had been completed- just as transistors replaced vacuum tubes and killed the project.  These now redundant gensets were then supplied to university heat engine laboratories all over the world.   One that came to Canterbury University in Christchurch New Zealand is on display in this collection. 

Philips went on to develop Stirling engines for many uses; ships, cars, satellites and etc.  Their licensees during the 1950 to 1990 period included Ford, GM, DAF, MAN, NASA and others.  None of these developments resulted in successful commercial products, except engines for (very quiet) submarines, which remain shrouded in secrecy.

However, their cryocooler division (sold in 1990) was very successful and is believed, along with license fees, to have returned sufficient to cover all their Stirling engine research.  The Philips body of research, shared with their many licensees, has formed a solid base for other Stirling engine and cryocooler developers.

As a converted cryocooler, this unit is intended as a demonstration of the reversibility of the Stirling cycle rather than state-of-the-art output and efficiency.  It runs very well and with a more powerful heater and boosted pressurisation has useful output.  

Peter Lynn for the Mahan Heritage Centre, August 2023