8.3 Can I prevent carburetter icing?
Description
This article is from the Gasoline FAQ, by Bruce Hamilton with numerous contributions by others.
8.3 Can I prevent carburetter icing?
Yes, carburettor icing is caused by the combination of highly volatile fuel,
high humidity and low ambient temperature. The extent of cooling, caused by
the latent heat of the vaporised gasoline in the carburettor, can be as much
as 20C, perhaps dropping below the dew point of the charge. If this happens,
water will condense on the cooler carburettor surfaces, and will freeze if
the temperature is low enough. The fuel volatility can not always be reduced
to eliminate icing, so anti-icing additives are used. In the US, anti-icing
additives are seldom required because of the widespread use heated intake
air and fuel injection [28].
Two types of additive are added to gasoline to inhibit icing:-
- surfactants that form a monomolecular layer over the metal parts that
inhibits ice crystal formation. These are usually added at concentrations
of 30-150 ppm.
- cryoscopic additives that depress the freezing point of the condensed water
so that it does not turn to ice. Alcohols ( methanol, iso-propyl alcohol,
etc. ) and glycols ( hexylene glycol, dipropylene glycol ) are used at
concentrations of 0.03% - 1%.
If you have icing problems, the addition of 100-200mls of alcohol to a full
tank of dry gasoline will prevent icing under moderately-cold conditions.
If you believe there is a small amount of water in the fuel tank, add 500mls
of anhydrous isopropyl alcohol as the first treatment, and isopropyl
alcohol is also preferred for more severe conditions. Oxygenated gasolines
using alcohols can also be used. It's important to ensure the alcohol is
anhydrous, as some grades contain up to 30% water.
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