Date

2021-9

Author

Özkan Özer, Melike

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This study is conducted to develop a model for the parameters that determine the ignition delay time during hypergolic combustion of liquid bipropellants in rocket engines. Hypergolic combustion utilizes the heat of mixing between the fuel and the oxidizer for ignition. A model study is conducted in order to understand the role of heat of mixing on the final temperature and final distribution of species between a vapor and a liquid phase. Water and nitric acid were selected as model compounds, due to the availability of the data and similarity of the system to binary liquid propellants. In order to be able to generalize the conclusions, alternative methods were used to obtain mixture state energies and vapor-liquid equilibrium data. Two constant Margules, van Laar and UNIFAC binary activity coefficient models were used to estimate both excess Gibbs free energy of the selected mixture and its vapor-liquid equilibrium. Moreover, density functional theory (DFT) estimations were performed using Gaussian09 software to estimate enthalpy, entropy, Gibbs free energy and binding energy upon mixing. The predictions were compared to the experimental data. A simple calorimetry sys tem was constructed to measure the mixing enthalpy. The measured values are com pared with the estimations. The experimental heat of mixing data was compared with DFT results. Although the estimations showed similar behavior in trend, it was shown that the estimations by DFT is almost eight times larger in magnitude than experimental results. Estimation models were also used and compared with the experimental data. The methodology developed in this study can be extended to estimate the behavior of binary liquid propellants and their ignition delay times.

Subject Keywords

Mixing enthalpy, Binary activity coefficients, Hypergolic ignition

URI

https://hdl.handle.net/11511/94240

Collections

Graduate School of Natural and Applied Sciences, Thesis