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All kind of Rankine or steam engines need a suitable fluid, that reacts to heating with an increase in pressure. The increased pressure of the fluid will be used to drive a piston, a turbine blade, lift a mass … and generate power. In this sense the fluid can be called “power fluid”. The following charts show graphs of the vapor pressure (bar) versus the temperatures (°C) for several fluids. The second chart uses a logarithmic vertical axis.




       The fluids are:

1. Propan – C3H8
2. Refrigerant R134a
3. N-Butan – C4H10
4. Refgrigerant R254fa
5. Dichlormethan (Methylenchlorid) – CH2Cl2
6. Aceton – C3H6O
7. Methanol – CH4O


The solid red curve shows the pressure rise of normal air resulting from isochoric (constant volume) heating. Note: this is only a limited collection and not all of those fluid have been tested for a steam engine application.



Steam Pressure



Steam Pressure Log