Researches Of The Influence Of Microorganism In Aircraft Fuel System

Aircraft fuel system's main function is to store and supply jet fuel safely and reliablely, according to the need of pressure, flow rate, and the permissive flight status, environment. The fuel tank in civil aircraft, usually uses the aircraft structure to make up the fuel tank, such as the both wings and body of plane. Commonly used in aircraft structure material, 7075 aluminum alloy and 2024 aluminum alloy are researched in this paper.The structure of civil aircraft fuel tanks and the flight environment determine the aviation fuel would inevitably contain water. Due to the density of water is bigger than jet fuel, water will settle down at the bottom of the tank, to form the aviation fuel-water system.Jet fuel is rich in essential nutrients of microbes, once the condition is met, such as temperature, moisture, microorganism will be infested.Microbial plugging and corrosion of the fuel system are relatively serious problems, which have serious consequences for the flight safety. Sulfate reducing bacteria(SRB) cause fuel tank corrosion, which phenomenon is very common.First, taking MM2 test results and biological microscope count microorganism quantity as two kinds of evaluation criterion, we select the optimal experimental system that can both simulate jet fuel-water environment in tank and suitable for growth of microorganism, and the SRB growth curve is researched in this experimental system.Then, microbiological corrosion behavior of aluminum alloy in jet fuel-water system is researched, Macro morphology and microscopic morphology of corrosion in different time are observed, compared with blank group, we found that corrosion current density of aluminum alloy first increases and then decreases, which is consistent with SRB quantity change rule. SRB promotes depolarization and S2-as the metabolite of SRB, which accelerates the pitting corrosion of aluminum alloy.After that, under the conditions of oxygen-enriched and anaerobic environment, aluminum alloy microbial corrosion evolution process and products of composition analysis, electrochemical test are compared. Results show that SRB in oxygen-enriched environment causes less corrosion degree, and SRB in anaerobic environment promote the aluminum alloy corrosion.Finally, studied the microbial corrosion behavior of aluminum alloy at different temperatures, HITACHIS-4800,CHI660 D are employed to study the surface of morphology and composition and the electrochemical corrosion behavior of aluminum alloy. Results show at low temperature microorganisms in groups adhere to the substrate surface. At 30?, the corrosion current density is the largest, capacitive reactance is minimum. SRB metabolic activity accelerates, membrane damaged then pitting appears. S,C elements are found in corrosion products.