The Effects of Particulate Contamination and Jet Fuel Chemistry on the Nucleation of Water and Ice in Aircraft Fuel Systems

该项目是正在进行的全面改善航空安全、飞机可靠性和减少维修费用的工作的一部分。人们早就知道航空燃料供应和飞机燃料系统中存在水，但事实证明，控制或消除水的成本效益高的措施极为困难。目前，飞机燃料供应要经过一系列旨在去除固体颗粒和游离水的过滤器，在加油之前进行简单的通/止测试以确定游离水的存在。随后，水可以通过燃料箱通风口以蒸汽形式进入飞机燃料箱，沿着空气中的灰尘、细菌、花粉和微小昆虫;然而，没有针对这些污染物的机载监测系统。目前的操作要求要求飞机定期停止使用，以便进行油箱排放试验和油箱内部的目视检查。自由水的痕迹通常不会太麻烦，但如果在低温下形成冰，这可能会造成严重的后果。一个合理的方法可能是接受水不可能完全消除的事实，但是设计操作方案，确保水和水污染的副产品不会危及航空安全和可靠性。除了上述之外，喷气燃料的成分多年来由于原油来源的变化而发生了微妙的变化，改进炼油厂的做法和引进来自可再生资源的烃原料。这些因素中的每一个都对水如何溶解在燃料中产生影响，并决定了水脱落或去除的前景。这一领域的数据大多是经验性的，对水分子如何在燃料中迁移并聚集形成水滴的真正理解很少。该项目的主要目标是研究喷气燃料的化学成分、飞机燃料系统中不同类型的表面（飞机结构和颗粒）以及溶解或夹带在燃料中的水之间的相互作用。这项工作将包括一系列化学和物理技术，以确定驱动水溶解，迁移和水脱落的关键参数。测试将在0 ℃以下的温度下进行，以确定导致冰形成的条件和冰的形式。学生将使用化学分析技术，如气相色谱法和卡尔·费休库仑法，以及物理技术，如冷台显微镜和颗粒计数。目前，可以观察直径超过1微米的喷气燃料中水滴的生长，并推断这些水滴可能是如何以及在何处成核的。项目的新奇之处在于能够准确地识别这些水滴如何以及为什么成核，以及当冰晶发展并开始生长时，是什么驱动了随后的水迁移。

The project is part of the ongoing general improvements to aviation safety, aircraft reliability and reduction in maintenance costs. The existence of water in aviation fuel supplies and aircraft fuel systems has been known about for a long time, but cost-effective measures to control or eliminate water have proved extremely difficult. At present, aircraft fuel supplies are subject to a series of filters intended to remove solid particulates and free water, with a simple go/no-go test for the presence of free water prior to refuelling. Water can subsequently enter aircraft fuel tanks as vapour via fuel tank vents, along with airborne dust, bacteria, pollen and tiny insects; however, there is no on-board monitoring system for these contaminants. Current operating requirements dictate that aircraft are taken out of service regularly for fuel tank drain tests and visual inspection of fuel tank interiors.Traces of free water are usually not too troublesome, but if ice is formed at low temperatures this can have serious consequences. A rational approach may be to accept that water cannot be totally eliminated, but to devise operating schemes that ensure that water, and the by-products of water contamination, does not compromise aviation safety and reliability.In addition to the above, the compositions of jet fuels have changed subtly over the years due to changes in sources of crude petroleum, modifications to refinery practices and the introduction of hydrocarbon feedstocks from renewable sources. Each of these factors has an impact on how water is solubilised in the fuel and determines the prospects for water shedding or removal. Data in this area is mostly of an empirical nature with very little true understanding of how water molecules migrate through the fuel and aggregate to form water droplets.The key objectives of the project are to investigate interactions between the chemical constituents of jet fuel, the different types of surface in an aircraft fuel system (aircraft structure and particulates) and water that is dissolved or entrained in the fuel. The work will encompass a range of chemical and physical techniques to identify the critical parameters that drive water solution, migration and water shedding. Tests will be carried at temperatures below 0C to identify the conditions that lead to ice formation and the form that the ice takes. The student will use chemical analytical techniques such as gas chromatography and Karl Fischer coulometry alongside physical techniques such as cold stage microscopy and particle counting.Currently it is possible to observe the growth of water droplets from jet fuel which are above 1 micron in diameter, and to infer how and where these droplets may have been nucleated. Project novelty lies in being able to identify exactly how and why these droplets nucleate and what drives subsequent water migration when ice crystals develop and start to grow.