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IS MEASURING JET FUEL VISCOSITY MORE ACCURATE THAN FREEZING POINT?


During their 2008 meeting in Shanghai, China, the International Air Transport Association (IATA) asked the Coordinating Research Council (CRC) to investigate the possibility of fi nding a replacement for the currently used freezing point methods. This request arose from the work of IATA’s Freezing Point Harmonization Group, whose goal was to explore the viability of using a single grade of commercial jet fuel throughout the world, with respect to freezing point.1


commercial jet fuel globally would have economic and fuel production benefi ts.


The group investigated a number of options, focusing on freezing points around Jet A and Jet A-1 limits. Although several options were presented and further study was suggested, the group’s work also indicated that the engine original equipment manufacturers (OEMs) were more concerned about the fuel viscosity at the engine intake rather than the freezing point of the fuel in the tanks. The report concluded that “it is a generally accepted fact that the freezing point test is not an effective test for predicting fuel fl ow behavior in the aircraft at low temperatures.”2


From this request came a comprehensive CRC report that evaluated the current state of the OEM fuel systems, available testing methods, and research into jet fuel low temperature properties.3


The report recommended four specifi c actions:


• Develop and assess a suitable low temperature scanning viscometer to accurately predict low temperature pumpability • Identify a viscosity equivalent limit for specifi cation purposes • Quantify any likely small chemistry changes to viscosity • Evaluate OEM support for replacing freezing point with viscosity


One of the conclusions from the CRC report was that


viscosity may be a more accurate predictor of pumpability from an aircraft fuel tank than freezing point.


A promising new instrument for simultaneously measuring freezing point, viscosity and density, which is approved for jet fuel certifi cation, is the Phase JFA-70Xi. This instrument combines a well-established freezing point test method (ASTM D5972/IP435) and a recently-developed viscosity test method (ASTM D7945) into a single instrument. The JFA-70Xi is capable of determining the kinematic viscosities of jet fuels at both -20°C and -40°C. It also measures the density of the fuel.


D7945 utilises a horizontal capillary and calibrated air pressure to drive a column of test sample. Under the Hage-Poiseuille principle, the times of transit across multiple calibrated timing segments are directly correlated to the viscosity of the fuel.


A 2016 ASTM ILS4 with current jet fuel types, including Jet A, jet


A1 (both satisfying D1655), renewables (satisfying D7566) and 50/50 blends, has demonstrated that D7945 exceeds the precision of both D445 and D7042, two other viscosity test methods. The repeatability of D7945 at -20°C is 0.011 mm2 reproducibility is 0.021 mm2


/s and the /s. This is more than four times better


The thought was that using a single grade of


The working principle of D7945, in which a fi xed volume of test fuel is driven by a calibrated air pressure force across timed segments of a horizontal capillary tube, The times of transit of the sample can then be used to calculate its viscosity according to the Hagen-Poiseuille law.


AUGUST / SEPTEMBER • WWW.PETRO-ONLINE.COM


JFA-70Xi, the world’s fi rst 3-in-1 Jet Fuel Analyzer


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