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The US National Academies of Sciences, Engineering, and Medicine in a 2015 paper described the concept of the fuel supply chain from refinery to an aircraft as “fairly simple and straightforward”. However, it did recognise that the actual delivery of clean fuel involves numerous processes, and that the possibility of fuel contamination exists every time the fuel is transferred.

To combat potential fuel contamination, the idea of ‘settling time’ was introduced for fuel in airport tanks in the 1950s. This procedure required fuel to be stored for one hour for each foot of depth in the fuel tank to allow sediment and moisture to settle at the bottom.

However, this approach, which was more of a ‘rule of thumb’ than an exact science, added significant time into the fuel supply cycle and required extra airfield tank capacity, both of which impacted on the efficiency of airport refuelling operations.

In the 1960s, Shell Aviation decided to look at the issue further to see if the process could be made more efficient. It conducted in-depth research into the settling behaviour of fuels with the aim of improving operational efficiency. A new device, The Shell Depth Sampler, was developed to take small samples of fuel from tanks at different depths, both simplifying the procedure and improving the reliability of sampling.

The research showed that fuel quality was not improved significantly with longer settling periods. Both aviation fuel and the systems used to transport and store it were significantly cleaner by the 1960s than in previous decades. This meant that most contamination was in the form of fine material held in suspension, which could not be removed by settling. With more modern fuel filtration equipment now available, these particles could be removed effectively by microfiltration during fuelling itself.

Shell’s detailed research into fuel settling enabled the aviation industry to progress from an outdated practice, contributing to the development of the safer, more efficient fuelling systems we know and rely on today. Today, Shell Aviation continues to make a contribution to efficiency and safety in aviation by its involvement in bodies such as the Joint Inspection Group (JIG), The Energy Institute and ASTM, helping set standards and regulations for operations at airports.

Sources:

_{Shell Aviation News, 1967, p. 243-254.
Shell historical archives.}