Abstract
This work determined a chemical mechanism for the early stage of hypergolic ignition following contact between hydrazine (N2H4) and nitrogen tetroxide (N2O4), both in the liquid state. Such mixtures have been used in thrusters for spacecraft applications for many years, and the effective development and use of such propellants requires an understanding of their detonation-like ignition under various conditions. Liquid-phase reactions were investigated using quantum chemical calculations at the CBS-QB3//ωB97X-D/SMD level of theory, and the results showed that the energy barrier to the reaction N2H4 + N2O4 → NH2NHNO2 + HNO2 was much lower than values predicted for the same reaction in the gas phase. Based on these results, a detailed kinetic model for the liquid-phase reaction was constructed and employed to predict the temperature increase obtained from N2H4/N2O4 propellants under pre-mixed and adiabatic conditions. The time to reach the N2H4 boiling point of 114 °C was estimated at approximately 0.06 μs, which explains the rapid formation of a vapor phase in previous droplet pool tests. Analyses of the rate of production and the temperature sensitivity established that the N2H4 + N2O4 → NH2NHNO2 + HNO2 step plays the most important role in triggering a series of subsequent reactions, and thus determines the rate of temperature rise.
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