Hydrazine (N2H4) is a propellant that is used in propulsion systems for spacecraft due to its ability to be utilized for both monopropellant applications, with the aid of a catalyst, and as a hypergolic bipropellant, when combined with the oxidizer nitrogen tetroxide. Since it is the propellant of choice for in-space thruster applications, a detailed knowledge of the thermal properties of liquid hydrazine is of major interest to aid in the designing of propulsion systems. The numerical analysis of propulsion system designs typically requires the use of a mathematical based equation of state for hydrazine. To validate the performance of an equation of state for a substance a detailed knowledge of the vapor pressure is typically required.
The vapor pressure of hydrazine has been experimentally measured many times previously. Reviewers have questioned the source of one of the published data sets, concluding that while the data set is fit well by the interpolating functions it is uncertain the exact origin and it is not known if the data is really experimental in origin or simply an extrapolation of existing experimental data. The data set in question includes nearly all of the experimental data recorded for hydrazine's vapor pressure above the normal boiling point (387.3 K). The only other existing experimental data points above the normal boiling point was conducted back in the 19th century. Collecting experimental data above the normal boiling point is of interest for calculating the liquid vapor interaction of hydrazine in high pressure environments such as those found in the injector and film cooling environment of an in-space propulsion system. Data above the normal boiling point has likely not been measured again due to the unstable nature of hydrazine which makes it an explosive hazard. In addition, hydrazine vapor tends to decompose at these elevated temperatures on most surfaces making such data collection challenging.
The current experiments measured the vapor pressure above the normal boiling point for the first time since 1896. The temperature range covered was 324 K which is below the normal boiling point to 414 K. Decomposition was observed to occur in the vapor phase at elevated temperatures which complicated the data acquisition and interpretation at these elevated temperatures. The current data set agreed well with the previous experimental measurements and the adjusted values for hydrazine's vapor pressure. A new vapor pressure correlation function was produced for hydrazine that fits well with both the current experimental data, the previously reported experimental data, and the adjusted values.
Dr. Brian B. Brady is a Senior Scientist at the Aerospace Corporation. Brian is currently investigating hybrid rocket motor testing, methane coking rates, and green propellant properties in a new propulsion research facility. He has investigated the properties of solid rocket propellants, hypergolic propellants, alternative propellants, and monopropellants. He has also been part of many anomaly investigations for launch vehicles and in-space propulsion systems. Brian was a Postdoctoral fellow at the University of Chicago where he corrected a major error in scientific literature by identifying source of an inaccurately assigned spectrum. He also automated calibration and scanning of laser doubling crystals and etalons, and improved sample preparation and analysis techniques. Brian received his Ph.D. from Columbia University in 1986. His thesis was on energy transfer rates measured with laser diagnostics. Brian earned a bachelor's degree in Chemistry from the University of Pennsylvania in 1981.
