You need a degree in chemistry or physics to understand the factors that could affect carburetor icing. Here is a little run-down about
fuel, detonation, pre-ignition, etc . The following explanation is extracted from the link above:
Can I prevent carburetor icing?
Yes, carburetor 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 vaporized gasoline in the carburetor, can be as much as 20C, perhaps dropping below the dew point of the charge. If this happens, water will condense on the cooler carburetor 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.
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 alcohols 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 isopropyl alcohol as the first treatment, and isopropyl alcohol is also preferred for more severe conditions. Oxygenated gasolines using alcohols can also be used.
And, if you want to continue the lesson, read about
a rich mixture and carburetor icing. Curmudgeon
