Aviation fuel cleanliness


Courtesy of Courtesy of Energy Institute (EI)

This autumn sees the launch of the second edition of the EI’s handbook, 1550; a title which has become a key industry reference for everyone involved in handling aviation fuel since the first edition was issued in 2007. Martin Hunnybun, EI Technical Team Manager – Fuels & Fuel Handling, describes the new content.

With over 20 specified performance parameters, jet fuel is one of the most highly specified fuels. All but one of these parameters have quantifiable limits that are measured by a range of well-defined analytical test methods. The single exception is fuel cleanliness. Whilst the other parameters remain relatively unchanged from the batch process at the refinery until delivery to aircraft, it is inevitable that cleanliness is affected by the entrainment of particulate matter, dispersed water and microbiological growth.

The aviation fuel supply industry uses stringent quality assurance procedures, along with filtration and water separation equipment deployed throughout aviation fuel supply chains, to ensure that into-plane requirements for fuel cleanliness are always achieved.

How clean is clean?

Quality assurance procedures incorporate requirements for the visual assessment of fuel samples to confirm they are ‘clear and bright’. This visual method establishes that the fuel is free from particulate matter that is greater than 40–50 microns (limitation of detection by the human eye). Aviation fuel handling infrastructure utilises fine filtration systems that may have nominal ratings down to 1 micron. This is 10 times smaller than white blood cells, some pollen grains and bacteria, and is in the size range of particles that are removed by surgical masks (1–3 microns). The schematic in Figure 1 attempts to put these sizes in context compared with an enlarged version of the blue circle in the EI logo which measures approximately 1 mm in diameter.

The scale of the cleanliness challenge reflects extended, complex supply chains involving multiple modes of transport, ageing infrastructure and the demand to provide 6mn l/d of jet fuel to aircraft worldwide (8,000 litres every second).

Disseminating good practice

The EI’s Aviation Committee has been responsible for defining and disseminating good practice for aviation fuel handling for many decades. Within the portfolio of publications are several laboratory performance test protocols/specifications that define minimum requirements for aviation fuel filtration systems. EI 1550 Handbook on equipment used for the maintenance and delivery of clean aviation fuel was first added to the portfolio in 2007, and has since become one of the most widely distributed EI publications. More recently it has been cited by the International Civil Aviation Organization (ICAO) in Doc 9977 Manual on ctvll aviation jet fuel supply. El 1550 provides an overview of the technical requirements contained in the aviation fuel filter specifications, specifically intended for users {rather than equipment manufacturers) and goes onto define good practice in the implementation and operation of filtration systems.

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