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Philips Stirling hot gas engine with rhomboid drive

Diagram of Philips Stirling hot gas engine with rhomboid drive

The four phases of the operating cycle of a Philips Stirling hot gas engine with rhomboid
drive; and a survey of the engine's construction

1. power piston 4. displacer piston 7. cold space 10. regenerator
2. hollow piston rod of 1. 5. piston rod of 4. passing through 2. 8. hot space 11. cooler
3. crank (two of) 6. gear wheel on the crankrod (two of)
(to ensure synchronisation of the two cranks 3.)
9. heater 12. rhomboid connecting rods (four of)

The development of the Philips Stirling hot gas engine was started in 1938. Shortly after World War II, the first prototypes were presented. These featured a rhomboid drive. In 1975, a horizontal 4-cylinder was built with 115 hp at 3,200 rpm. It used helium at 140 bar (maximum) and reached 40% efficiency.


Phase 1. The displacer piston 4. is in its upper position; the power piston 1. is in its lowest position. All of the gas is in the cold space 7.

Phase 2. The displacer piston 4. remains at the top while the power piston 1., moving upwards, compresses the gas in the cold space 7. The gas starts flowing through the regenerator 10. towards the hot space 8. It is heated in the heater 9.

Phase 3. The power piston 1. has reached the upper position and all gas is now passed through the regenerator 10. and heater 9. into the hot space 8.

Phase 4. The hot gas in hot space 8. starts to expand and pushes both the displacer piston 4. and the power piston 1. downwards to their lowest positions. The displacer piston 4. moves back up again and pushes the now expanded gas through the regenerator 10. towards the cold space 7. It is cooled in the cooler 11.

The regenerator is an essential part of any hot gas engine. As an accumulator, it recycles much (up to 95%) of the heat between hot and cold gas, so improving efficiency of the cycle. The gas used in the Philips Stirling engine is helium. Being a mono-atomic gas, this allows lower operating temperatures than air.

Principle of "rolling stocking" seal

The engine parts exposed to high temperatures are made in special heat resistant materials. The seals are very important in a hot gas engine: low friction and good sealing properties at high pressures are of the essence. The Philips Stirling engine used nylon "rolling stocking" seals, thin nylon tubes rolled back upon themselves, rolling in and out with the up and down piston movement.

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