Freezing point

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The term Freezing Point, which comes from English, generally means the freezing point of liquids .

Technical terminology for aviation fuels

The Freezing Point (FRP; also Freeze Point ) describes a cold property of jet and AvGas aircraft fuels. It represents the lowest temperature at which fuel is still liquid. At lower temperatures, paraffins crystallize out . The official German translation is: freezing point . Sometimes the point of failure is spoken of.

determination

For the determination of the freezing point (see also: ASTM D 2386), a sample is cooled under defined conditions until they through the formation of paraffin crystals hazy or cloudy (see also: Cloud Point ). The sample is then reheated. The temperature at which the sample appears clear again is known as the freezing point. Nowadays the measurement is carried out automatically with the help of photocells.

FRP vs. Pour point

Since aviation fuel is a mixture of many different substances, it is not possible to specify a freezing point in the thermodynamic sense, only a freezing or melting interval. The freezing point is the upper temperature of this temperature interval (in fact, even slightly above this interval). The lower temperature of the interval is called the pour point. According to the pour point, the pour point is approx. 9–12 ° C below the freezing point (see also: pour point ). The unfortunate formation of terms in English and the direct German translation could give the impression that the kerosene is solidifying just below the FRP. That is not correct, only very small amounts of paraffin solidify.

FRP vs. Cloud point

In the case of diesel fuel , EL heating oil and various types of marine diesel oil , the upper temperature of the melting interval is called the cloud point. It is determined in a similar way to the FRP (possibly with the same multifunctional apparatus).

Significance in aviation

In addition to the flash point, the FRP is the most important safety-relevant quality of the various jet grades. It indicates the temperature at which fuel filters and injection nozzles can clog. Pilots are required to never let the kerosene temperature drop below FRP + 3 Kelvin. If you get into this critical situation, you have to fly lower or faster. This increases the air friction on the outer skin, and the heat generated in this way raises the temperature.

Additives that improve the FRP are not permitted in the jet grades.

Individual evidence

  1. ↑ Leo: Translation of Freezing Point .
  2. ↑ ISO 3013: 1997-09  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. .@1@ 2Template: Toter Link / www.beuth.de  
  3. ↑ ASTM standard .
  4. ↑ a b c d Safety recommendations .