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Re: [Phys-L] weather, school, and cars



On 01/27/2014 08:10 PM, Anthony Lapinski wrote:

Is this additive really necessary since
gasoline, depending on the type, generally freezes at a very low
temperature (-72 °C)? And does this depend on how full the gas tank is?

Here's the deal:
a) Gasoline can dissolve a nontrivial percentage of water.
b) The amount is strongly dependent on temperature.

There are lots of scenarios where gasoline can pick up
water from the environment on warm days. A car that
sits around has issues ... and the distribution industry
has issues, too.

Then when it gets cold the water precipitates out. This
is bad enough, because it can cause the engine to hesitate
or stop outright. Then it gets colder and the water freezes,
blocking the lines.

Alcohol and water are miscible in all proportions, and
mixing lowers the freezing point, so adding alcohol is
in fact the second-best way to alleviate the problem.
The best way is to keep water out of the system from
the beginning.

It's tricky to google for data on this, since people
are far more interested in gasoline dissolved in water,
for obvious pollution-related reasons.

There are however things like this:
T.M. Letcher,
C. Heyward,
S. Wootton,
B. Shuttleworth
"Ternary phase diagrams for gasoline-water-alcohol mixtures"
http://www.sciencedirect.com/science/article/pii/0016236186901924