| The flammable and explosive characteristics of fuel tank seriously threaten the safety of aircraft,so some measures must be taken.Generally,the hollow fiber membrane On-board Inert Gas Generation System?OBIGGS?is one of the most widely used fuel tank inerting technologies.The latest researches show that the oxygen consumed inerting technology,based on flameless catalytic combustion,is potential owning to its simple structure,high efficiency and low fuel penalty compared with the OBIGGS.However,the inert gas in oxygen consumed inerting system is the Mixed Inert Gas?MIG?,which is consisted of CO2 and N2,rather than Nitrogen-Enriched Air?NEA?in the OBIGGS,thus,some new problems should be solved.In order to control the oxygen concentration level on ullage,it does not only need to master the dissolution and evolution characteristics of gases,such as O2,N2 and CO2,but also needs to investigate the various inerting methods and capabilities between MIG and NEA.Due to deficiencies in current research works of the oxygen consumed inerting technology,an experimental apparatus was constructed to systematically investigate the dissolution and evolution of O2,N2 and CO2,the effects of MIG on ullage washing and fuel scrubbing,and inerting capability between MIG and NEA.The solubility and diffusion coefficient of gases in domestic jet fuel were measured,and the theoretical model of oxygen consumed inerting technology was established.Additionally,the further studies were conducted on the system design,performance analysis and selection of inerting method for oxygen consumed inerting technology.The main work and achievements are as follows:?1?A pressure drop experimental apparatus was established.The Ostwald coefficients of O2?N2and CO2 in RP-3 jet fuel were measured under various temperatures and pressures.The empirical formula given by ASTM D2779-92 was modified based on the measured data to better reflect the characteristics of gas dissolution and evolution in domestic fuel,the results show that the modified formula proposed in this paper can increase the calculation accuracy of Ostwald coefficient of N2 and CO2 by 10%and 14%,respectively.Furthermore,the diffusion coefficients of O2?N2 and CO2 were also measured under different temperature.For the convenience of engineering applications,the experimental data fitting method was used to obtain the Arrhenius equation,which can predict the gas diffusion coefficient in RP-3 fuel at a certain temperature range.On this basis,this paper adopted the Fick diffusion theory to describe the characteristics of gas dissolution and evolution,the research results can provide support for theoretical modeling of ullage washing inerting process in non-equilibrium state.?2?The experimental research on the inerting capability of MIG and NEA was carried out by the establishment of the fuel scrubbing test bench,and the size and distribution of the scrubbing bubble were captured via the image processing technology.A scrubbing efficiency was defined,a theoretical analysis model for MIG scrubbing was established,and the calculation method of scrubbing efficiency based on Feret diameter was presented.The characteristics of gas dissolution/evolution and the requirement of gas quantity were studied during MIG and NEA scrubbing.The results show that the ullage and dissolved oxygen concentration of MIG scrubbing are always higher than that of NEA scrubbing.The scrubbing efficiency has an exponential relationship with Feret diameter,and decreasing rapidly as the Feret diameter increases.To achieve a higher scrubbing efficiency,when designing the fuel scrubber,it is recommended to set the target of Feret diameter below 0.2 mm.By using the fuel scrubbing inerting model established in this paper,it can predicts the variation of inerting parameters during the fuel scrubbing process with a high accuracy.The research achievements can provide a guidance for the design of the oxygen consumed inerting system and the fuel scrubber.?3?By establishing an experimental system of ullage washing,the inerting capability of MIG and NEA washing were experimentally investigated.Further more,this paper adopted the Fick diffusion theory to establish theoretical model of ullage washing inerting process in non-equilibrium state,and compared the characteristics of gas dissolution/evolution and the requirement of gas quantity during MIG and NEA washing.The results reveal that,when the inert gases have the same oxygen concentration,the inerting capability is nearly identical whatever the inert gas is NEA or MIG.When the fuel tank is inerted to 9%oxygen concentration,the quantity of MIG will be 6-14%higher than that of NEA,specifically,the higher CO2 concentration in MIG,the more inert gas requirement.When the CO2 concentration in the inert gas increases from 0%to 95%,the inert gas requirement will increase about 7.4-18.24%.Due to the influence of enhanced mass transfer?such as tank shaking,temperature changes,etc.?,the NEA requirement will increase slightly,while the MIG requirement will increase significantly.?4?Based on physicochemical characteristics of domestic jet fuel,an oxygen consumed inerting system with external air supply was presented,and the influence factors in the system were analyzed.In order to satisfy the requirement of flight mission,the various inerting methods were investigated at the actual flight process,and the optimal inerting method of the oxygen consumed inerting system which proposed in this paper was obtained.Additionally,through theoretical calculation and analysis,a comparative principle was conducted to quantitatively compare the performance between the OBIGGS and the oxygen consumed inerting system.The results reveal that the oxygen consumed inerting system with external air supply could make the inerting process more controllable.Compared with OBIGGS,the oxygen consumed inerting technology has obvious advantages at the aspect of air bleeding,system heat load and fuel compensation,moreover,the advantage is more obvious as the inerting time decreases. |
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