How does carburetor icing occur at 80 degrees Fahrenheit?

Question

It is explained in Bournouli's principle that there is a lower pressure by the curvature which makes the air cooler...causing ice even at high temperatures. Then how does the human body work? Our lungs, nasal cavities every hole in our body have archs and curves..why don't we get icing? Does this have to do with the altitude? So will our bodies burst because of the properties of water (water molecules expands when frozen)?

Answer 1

One disadvantage of the float-type carburetor is its
icing tendency. Carburetor ice occurs due to the effect
of fuel vaporization and the decrease in air pressure in
the venturi, which causes a sharp temperature drop in
the carburetor. If water vapor in the air condenses when
the carburetor temperature is at or below freezing, ice
may form on internal surfaces of the carburetor,
including the throttle valve.

The reduced air pressure, as well as the vaporization of
fuel, contributes to the temperature decrease in the
carburetor. Ice generally forms in the vicinity of the
throttle valve and in the venturi throat. This restricts
the flow of the fuel/air mixture and reduces power. If
enough ice builds up, the engine may cease to operate.
Carburetor ice is most likely to occur when
temperatures are below 70°F (21°C) and the relative
humidity is above 80 percent. However, due to the
sudden cooling that takes place in the carburetor, icing
can occur even with temperatures as high as 100°F
(38°C) and humidity as low as 50 percent. This
temperature drop can be as much as 60 to 70°F.
Therefore, at an outside air temperature of 100°F, a
temperature drop of 70°F results in an air temperature
in the carburetor of 30°F.

Answer 2

It's actually a combination of things.

First off, the carburetor pulls a much stronger vacuum than than your lungs can. You never generate enough change in air pressure to noticeably affect the air temperature. But a carburetor can and does.

Then, there's the gasoline. The carburetor makes that vacuum so it can suck the gasoline into the airstream and vaporize it. As the gasoline vaporizes it cools the air. So the air inside the carburetor gets much cooler, quickly. When you combine that with the drop in air pressure, the inside of the carburetor is much cooler than the outside.

Now add in the fact that the air outside can be not only warm but moist. Get that moist air cold enough (and the vacuum and vaporizing gasoline can do it) and the water in the air can freeze as it's passing through the carburetor. The ice builds up inside the air passages and chokes them up. No airflow, no air in the engine, no vacuum to suck gasoline vapor into the cylinders--and the engine quits. It doesn't take much ice to do it.

That's why the best conditions for icing involve higher temperatures than you expect, especially on days with lots of humidity.

Answer 3

1. warm air carries more moisture than cold air. Therefore, think of 80 deg F air as "wetter" than 32 deg F air.

2. gas under high pressure contains more heat than gas under low pressure.

When gas under pressure is allowed to rapidly move to an area of much lower pressure, the gas must give off a tremendous amount of heat (# 2) which means it cools off rapidly...under the right conditions easily to below freezing. Carburetors, by definition, are open to the atmosphere which allows that very cold gas stream to come into contact with 80 deg F "wet" air. Given #1, the first thing that happens, as you probably have noted when you leave a cold glass of water outside on a warm day, condensation will form around the neck of the carburetor because the cooler air has to "let go" of the moisture it was carrying when it was warmer. The continuation of that very cold gas flow will begin to freeze the condensation on the neck and that additional cold surface area will cause more "wet" 80 deg F air to condense...which will freeze...and so on until you've collected enough ice to impede the flow through the carburetor. This a common problem when flying reciprocal engine airplanes at low throttle settings. I've seen many an airplane start sputtering on a nice warm Spring day when flying around in the pattern all day. The solution, at least in airplanes, is to use "Carb heat" which opens a damper to allow hot exhaust gases to flow over the carburetor to keep the neck hot.

Answer 4

Our bodies don't ice up simply because the pressure drop and therefore the temperature drop isn't as great as it is in the venturi of a carburetor.

Answer 5

Heck yeah Sunny, but not even as cold as 70. I love it when the temps are high.