Investigation Of A Nitrous Oxide Self-Pressurized Tank

Nitrous oxide?N₂O? self-pressurized feed system attracted many designers' attention due to its simplicity. Accurate modeling of propellant pressurization is essential for the predicting of engine's performance. This paper analyzed the performance of N₂ O self-pressurized tank with theoretical modeling and experiment, investigated the phase change in the tank during the self-pressurization progress and discussed partial characteristic of N₂ O tank in self-pressurization.To help modeling, Greg Zilliac's three regions assumption is used and we can divide the tank in liquid phase, vapor phase and the saturation region. Applying the law of mass and energy conservation to these regions, we can get the main equation of the model in my paper. At first the Peng-Robinson equation of state and the series of calculation forms of internal energy and enthalpy are used to solve the model. Since the inconvenience of the existing of derivatives of densities and volumes in the right side of equation when integrating with time using Runge-Kutta methods, the model is further deduced with the Peng-Robinson equation of state and formed the Peng-Robinson model of my paper. The effects of ambient temperature and fill levels of N₂ O in tank were analyzed with the calculation of initial state of tank and the influences of pressurized Helium to the state of tank were also investigated. Due to the imprecision in states near critical point of Peng-Robinson equation of state, A more accurate technical equation of state, the REFPROP was used, the model was also resumed to form the second model, the REFPROP model in my paper.To help modeling we also conducted the experiment. Since we assume the temperature distributed equally in the regions of vapor and liquid, but how the temperature distributed actually in the tank during the self-pressurization progress, this is the key point that we consider. So we builded a self-pressurization system, and a series temperature sensors were distributed equally along the axial direction of N₂ O tank, a set of load cells was used to measure the mass of the experimental system to get a more accurate mass flowrate. Using this experimental apparatus, we conducted the liquid blow-down tests, the vapor blow-down test, the continuously supercharged test of nitrogen and the initial equilibrium test and analyzed the phase change in the tank during these progresses. It turns out that the liquid temperature stratification is small or becomes small as the test begins. However, the vapor temperature is stratified because the temperature in the upper region decreases little and the temperature in the regions evacuated by liquid is low. The saturation temperature of N₂ O is between liquid and vapor temperature, and is closer to the liquid temperature. The pressurized nitrogen can change the temperature distribution in the tank but can hardly affect the temperature distribution in liquid region. When the initial state of tank reached equilibrium, the vapor temperature decreases little but the vapor temperature declines largely in the self-pressurization progress.At last, the models in this paper are used to model the tests above, and the influence of sensitivity parameters in the model is also analyzed. It turns out that you can always get satisfactory pressure and liquid temperature histories when using a suitable empirical factor in the model. The stratification in vapor region makes it dissatisfy the assumption of lumped parameter node, so the temperature differences in vapor can be predicted. The mass flow coefficient is sensitive to the model result so that it should be accurately measured in the test.