| The fire and explosion in aircraft fuel tank generally can be prevented with On-Board Inert Gas Generation System (OBIGGS) producing nitrogen enriched air (NEA) to control the oxygen concentration of the ullage. Using this method, we can achieve the purpose of fuel tank inerting. Fuel tank inerting can be divided into two parts, fuel washing and fuel scrubbing. This thesis will be started with two kinds of researches, one is an engineering calculation of an aircraft fuel tank scrubbing inerting, the other is numerical simulation of ground-based inerting and a whole flight profile inerting in a military aircraft fuel tank ullage.Firstly, based on consulting a large number of Chinese and foreign references, fuel scrubbing inerting would be transformed into a process, which was combined fuel scrubbing with ullage washing. Single tank scrubbing engineering model was built. By use of Delphi 7 software, engineering calculation software was worked out. Results of calculating were obtained quickly. The results of a single fuel tank were compared to the experimental data of the reference and calculated data from the existing research. In this way, the accuracy and the feasibility of this model were verified firmly. To explore the effects of different factors, the initial oxygen concentration of ullage, fuel loading rate and scrubbing efficiency were considered. It turned out that, scrubbing time would be saved with the lower initial ullage oxygen concentration. The oxygen volume fraction would be down faster with the rate of fuel load increased. Inerting time would be different under various scrubbing efficiency which representing nozzle types.Secondly, according to the distribution of an aircraft actual fuel tank, the engineering calculation of a complex multi-bay aircraft fuel tank could be realized based on the single fuel tank model. It turned out that, the ullage oxygen concentration of each bay in an aircraft fuel tank was related to the position of the NEA inlet and the volume of each bay. Multi-bay fuel tank scrubbing inerting was affected by scrubbing efficiency.Thirdly, computational fluid dynamics (CFD) method was used to establish the model of a military aircraft fuel tank inerting. Ground-based inerting of a fuel tank was analyzed. During this process, the dissolved oxygen in the fuel would be displaced with nitrogen and its volume could be computed according to engineering calculation. UDF was written to divide oxygen volume equally to ullage by the volume of each bay. The simulation of inerting flow in a military aircraft fuel tank ullage was carried out. Factors such as the rate of fuel load and the initial oxygen concentration of ullage were also studied in the thesis. The results indicated that the more of the rate of fuel load, the less of the inerting time. Inerting time would be longer if the initial ullage oxygen concentration increased. Ullage oxygen concentration was related to the volume and position of each bay.Finally, a military aircraft complex fuel tank inerting was simulated numerically under a flight profile. Some relative UDF programs were compiled to resolve problems like the evolution of fuel dissolved oxygen, the fuel level and the pressure of ullage. Changes of oxygen concentration in different flight stages were distinguished. Different rate of fuel load was studied as well during the fuel tank inerting. The emulation result showed that, oxygen concentration of each bay decreased but the falling rate was different for climb and cruise portions. In the descent portion of flight test, oxygen concentration was recovered because of the changes of ambient pressure, some air was forced into the ullage of the fuel tank. |
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