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

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.