Gasoline Freezing

Most recent answer: 10/22/2007

Q:
Why doesn’t gasoline freeze?
- Shelby (age 11)
Jacksonville, FL
A:
Well, gasoline should freeze if you get it cold enough! Gasoline does not consist of a single kind of molecule -- it contains several different hydrocarbons (molecules consisting of hydrogen and carbon atoms). In principle, if you cool a mixture like this slowly enough, it will form a collection of different types of frozen crystals, with the freezing of each type of crystal occurring over a (different) range of temperatures. In practice, often such mixtures don’t form crystals at all but just gradually thicken and harden as they get colder, forming something like glass- hard but without the regular crystal that make a true solid so different from a liquid. In a glass, on a small scale the molecules are still jumbled up like in a liquid.

The problem of fuel getting gummy and solidifying is more of a worry with aviation fuel. High-flying airplanes fly through very cold air (every time I fly and they show the outside temperature, it’s -80 F!). And one of the last things you want to happen to an airplane is for the fuel pipe to freeze up. People add stuff to aviation fuel to keep this from happening. Piston-powered propeller planes sometimes have isopropyl alcohol or other compounds added to prevent freezing.

Tom and mike

(published on 10/22/2007)