Thermodynamic equations of state for hydrazine and monomethylhydrazine

Abstract

Thermodynamic equations of state are evaluated for the aerospace fuels hydrazine and monomethylhydrazine using Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) formulations. The PR formulation is shown to be the best fit for hydrazine, and the SRK formulation to be the best fit for monomethylhydrazine, based on available critical property data and evaluations of thermodynamic consistency. The adequacy of the differing property data for these fuels in the literature is discussed, and the methodology used to validate the formulations is outlined. The importance of using appropriate real fluid equations of state in thermodynamic safety and hazards analysis of fuel systems is demonstrated by considering an adiabatic compression of gaseous fuels previously postulated in accident scenarios of aerospace propulsion systems. Calculation of isentropic compression temperatures for pure components using ideal gas constant heat capacity, ideal gas with variable heat capacity, and real fluid equations of state are compared to illustrate the need for real fluid equations of state. In addition, three separate approaches are used for estimating isentropic compression temperatures for mixtures involving these fuels, again illustrating the importance of treating these mixtures as real fluids for design and safety analysis.