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

The aviation industry is currently facing increasing environmental and energy challenges regarding its fuel use. Research is therefore currently under way to develop new sustainable aviation fuels. Understanding the properties of these fuels (along with the changing properties of existing fuel types) is required to understand their impact on aircraft fuel systems. Water solubility, water settling and ice formation in fuel are such properties of interest. The presence of water in jet fuel/fuel systems has been a long-standing issue in the aviation industry. Therefore, it is important to precisely identify the conditions and features that may exacerbate this phenomenon, understanding how fuel composition, temperature, water droplet sizes, flowrate and pipe surface affect ice formation and water solubility. Currently, there is relatively limited data regarding water solubility/settling rate and ice formation in sustainable fuels, specifically those specified in ASTM D7566. This work gives a comprehensive account of the recent advances and technologies in the literature indicating conditions that might lead to the nucleation of water and ice in aircraft fuel systems. These conditions have then been applied to characterizing dispersed water droplets in alternative fuels and conventional Jet A-1. Subsequently, the requirements have been applied to the design, set up, and effectiveness of an ice test rig to understand the types and amounts of ice that can be produced from different sustainable aviation fuel blends. In doing so, this work has helped shed light on the role of fuel composition in ice accretion and whether ice accumulation on a pump inlet strainer may impact pump performance. Furthermore, the results from this work will serve as a basis for design guidelines to minimise ice formation within an aircraft fuel system and help identify some potential/sustainable jet fuel candidates for ASTM D7566 certified jet fuels.Ph

Characterization of water droplets size distribution in aviation turbine fuel: ultrasonic homogeniser vs high shear speed mixer

Pumps, pressure drops across fittings, and flight operations (such as turning manoeuvres, take-off, and landing) are some of the many sources of turbulence mixing and shearing in aircraft fuel systems, therefore, making it an inevitable condition. Literature established that shearing conditions would influence the droplets and droplets size distribution in an oil/water emulsion. So, low intensity shearing conditions could be beneficial as it promotes droplets coalescence, which could be a driving force for a weak emulsion. However, to date no experimental data has shown the influence homogenising intensity and total water content has on dispersed water droplets size distribution in aviation fuel. Therefore, to expand knowledge of quantification of measurements of dispersed water droplets in aviation fuel, this study characterizes dispersed water droplets in aviation turbine fuel, varying available laboratory homogenising devices and water content. Results presented show that droplets count increases with water concentration and shearing effect. To provide more statistical evidence, kurtosis and skew values were calculated from the extrapolated data and compared with data from a hexanol/water mixture given that hexanol is likely to form a stable emulsion. Experimental results show that the higher the homogenising intensity the more stable the emulsion is likely to be with a higher kurtosis and skew value close to that for the hexanol/water mixture. Therefore, observations show that mild shearing conditions (high shear mixing in this case) could help promote droplets coalescence, leading to a better separation ability.Engineering and Physical Sciences Research Council (EPSRC): EP/N509127/1. Airbus Operations, Filton, Bristol (Reference ID: 1100152106), United Kingdom

Complexities associated with nucleation of water and ice from jet fuel in aircraft fuel systems: A critical review

The contamination and behaviour of water in aircraft fuel systems remains a significant global research interest following several aircraft incidents. To engineer a solution to the problem of icing in jet fuel, it is crucial to precisely identify the conditions and features that may exacerbate this phenomenon. This review will aid prospective researchers to identify work that has been done and work that is yet to be available for future study. In this review, conclusive data integrating a wide range of literature and also providing an in-depth description of the factors that influence the behaviour of trace water, ice formation in jet fuels was carefully summarised. On investigational studies, it was discovered that to date, no work is available that studies the impact of sustainable jet fuel and its blends on ice formation, size and frequency distribution of dispersed water droplets in aircraft fuel systems. Findings from comparative studies also reveal that surfaces will have an essential role in the growth pattern of ice in aircraft fuel systems. Furthermore, findings show that supercooled water droplets with sizes greater than or equal to 5 µm can induce ice accretion. This review identified a common problem with the prominent methods of reporting results as a graphically fitted plot. Subsequently, it proposed that authors of any original technical work provide raw data as supplementary information to allow comprehensibility. The study further offers a system that could help manage the nature of ice in aircraft fuel tank systems—making it readily available and accessible

Investigation of water droplet size distribution in conventional and sustainable aviation turbine fuels

Water droplet size variation has been established in the literature as an important variable that influences the behavior and characteristics of water in fuel emulsion. However, with the growing demand for sustainable aviation fuels (SAF), no data is available that shows how these fuels will affect the size of dispersed water droplets and their frequency distribution. To address this lack of knowledge, this study explores and presents experimental results on the characterization of dispersed water droplets in alternative fuels and Jet A-1 fuel under dynamic conditions. The alternative fuels comprised of two fully synthetic fuels, two fuels synthesized from bio-derived materials, and one bio-derived fuel. The data and statistics presented reveal that water droplet frequency and size distribution are sensitive to changes in fuel composition. Observations showed an evident transition of the droplet percentile over time in the cumulative frequency distribution; this could be attributed to droplet coalescence to form larger droplets. Mean droplet diameters between 3 and 6 μm were observed for all the fuels tested. With further analysis based on recommendations proposed in this work, the data may assist in providing insight to filter manufacturers