| Fuel tank blasting is one of the main reasons of aircraft accident. The existing studies haveshown that using Nitrogen Enriched Air (NEA) generated by On-Board Inert Gas Generation system(OBIGGS)to inert fuel tank is one of the most economical and effective ways of safety protection forfuel tank.This contains two ways: fuel scrubbing and ullage washing, while fuel scrubbing is mainly usedin military aircraft, ullage washing is widely used in civil aircraft.The so-called ullage washing refers to displace NEA on the fuel tank ullage to make andmaintain the oxygen concentration lower than the fuel burning limit.Taking the needs of domestic aircraft fuel tank inerting technology research into account, thispaper carry out a more in-depth study on the inerting flow field and influencing factors of the civilaircraft. The specific contents include:(1)Characteristics of oxygen and nitrogen dissolved in fuel are systematically summarized andtheoretical models of fuel washing applicable to a wider range are established. By comparing with theexiting experiment, the validity of the model has been verified. Numerical integration methods areused to study the variation of the oxygen concentration during the washing process.(2)By means of numerical simulation, the oxygen concentration variation of the single-bay andmulti-bay fuel tank inerting space is studied. The impact of factors such as flow rate, concentration ofNEA, velocity of NEA on fuel tank inerting is discussed. On this basis, new indices,“maximumoxygen concentration” and “percentage of inerting completion” are proposed to improve theevaluation system of inerting. Three-dimensional mathematical models, which combined withdomestic aircraft fuel tank structure, are built to carry out a study of washing process of the multi-bayfuel tank. Detailed information of oxygen concentration distribution in each bay at different times isobtained.(3) Taking a single-bay fuel tank ullage washing for example, a new concept------“mainstream”isdefined as the channel between inlet and outlet. Meanwhile, the optimal “mainstream” should occupythe area (volume) of the bay as much as possible. The Mechanism of flow changing during ullagewashing has been studied. Several numerical examples of a typical multi-bay tank inerting arecalculated. An airflow optimized design principles, which is of universal applicability, is put forwardand used in the airflow design of the aircraft fuel tank inerting and good results are achieved.(4) A series of experiment are carried: The gas flow visualization experiments verify the validityof the fluid flow calculation method; Liquid washing tracer experiments establish the qualitative understanding of the fluid washing process; The quantitative measurement of liquid concentrationprovide a good idea for tracer experiments of fluid and liquid concentration measurement, inparticular for transient concentration measurement. The experimental results further validate theproposed optimization principle.The results of this study provide a useful reference for large civil aircraft fuel tank inertingsystem design. |
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