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Airport Mean freezing point Standard deviation Max Min Average Give-away (*) Minimum Give-away (*)
Chicago (ORD) - 43.2 0.43 - 42.4 - 44.7 2.5 1.7
Dallas (DFW) -42.1 0.79 - 41.1 - 45.9 1.4 0.4
New York (JFK) - 45.2 0.36 - 44.1 - 46.0 4.5 3.4
Los Angeles (LAX) -50.9 2.13 - 46.8 - 58.2 10.2 6.1
San Francisco (SFO) -52.2 1.75 - 48.6 - 56.1 11.5 7.9
Miami (MIA) - 47.2 3.67 - 41.0 - 53.1 6.5 0.3
(*) Freezing point give-away is a term commonly used to denote the extent by which the actual measured freezing point of an aviation turbine fuel is lower than the specified value (here - 40°C for JET A). The average (minimum) give-away is derived from the mean (maximum) freezing point, but corrected for instrumental uncertainty to a confidence limit of 95%.
Another survey conducted in 1992 in United Kingdom on 1385 batches of JET A1 showed that the mean value was -51.8°C (for a specification limit of -47°C - see figure D6).
(Specification limit = - 47°C max, mean = - 51.8°C; standard deviation = 3.74°C)
Number of batches
35 28 21 14 7 0
-69 -67 -65 -63 -61 -59 -57 -55 -53 -51 -49 -47 (°C)
Figure D6 - Freezing point distribution - JET A1
D5.2 Mixing fuels
Based on the research done to-date, it is not really possible to predict the freezing point
of mixed fuels, even when the exact freezing points of all the individual components are
known.
It is tempting to assume that jet fuels form an ideal solution, since there is a linear
relationship between freezing point and blend concentration.
In reality, very few jet fuels behave ideally. Upon blending, freezing point elevation
(positive deviation from linearity) and depression (negative deviation) are often observed.
Figures D7
illustrate the results of a study conducted by .Phase Technology..
This study focused on 10 finished jet fuels produced by refineries in North America and
Europe. The fuel freezing points of these 10 fuels were measured. They were then
blended in different combinations and ratios, and the resulting freeze points of these
samples were measured.
Figure D7A
is the plot for blends made up of samples called A and H. Both A and H have
similar freeze points (-48.8 and -48.2 °C) in the JET A1 range. The concentration of fuel H
in the blend is shown on the horizontal axis. At 0% of H, the sample is made up of fuel A
only. At the other end of the scale is 100% H. This system is an example of freeze point
elevation. The freeze point of all the blends from these two fuels are consistently higher
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