Vapor pressure is the equilibrium pressure between evaporation and condensation above a fluid in a closed vessel at a constant pressure. This is an important property for safety, storage, and propellant feed system design, and it informs the volatility of liquid fuels. The vapor pressure testing ran from August 2023 through January 2024.

The setup employed an Agilent Technologies DS 42 dual-stage rotary van vacuum pump to evacuate the headspace in a round bottom flask containing the fuel sample. A UNIK 5000 vacuum pressure transducer and an Omega T-type thermocouple provided pressure and temperature measurements of the headspace and the fuel sample, respectively. The full setup is displayed in the figure to the right.

The stand was validated using de-ionized water. Experimental data was fit to the Antoine equation:

Measured values are compared against the data provided by the National Institute of Standards and Technology in the figure to the left. The Antoine equation fits for water result in a root mean square for error of 0.33 kPa and a 5.55% error from the expected mean value.