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RPM loss


Rich

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We seem to be looking at the fuel, first at the eathonal and now at the absorbed water in a thread about carb ice.  I think the source of moisture is condensation of the moisture in the atmosphere.

 

As far as our tanks being open, is that negated by the positive vapor pressure?

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Just another data point on carb ice, dew point, alcohol, and the 912... Interesting to say the least.

 

A direct quote from: http://www.rotaryforum.com/forum/showthread.php?t=32058

 

"Somrthing worthy of noting is a lots of times the moisture is in your fuel.
I well remember in northern alberta canada being in a service trruck that could barely run in-40 temps because of ice buildup in the venturi.
I had to remove the air breather and chip the ice away with a screwdriver in the venturi before moving on.
There is not much humidity in -40 air so it had to be in the fuel itself.
I blame that on how much gas line deicer (alcohol) is added into our fuel to make up for how much water is actually in it.
If I was to fill my paint sprayer half full of alcohol and then add a half of cup of water to it it would all mix.
I could even put some gasoline in with that and it would mix as well.
If I then took that same spraygun outside and sprayed that mixture against a piece of cold metal a snow cone would start to appear.
The water portion of the solution would freeze against the metal but the gas and alcohol parts would evaporate away!
You could use your favorite whiskey for this same test but that would be alcohol abuselol.gif
One thing that always puzzled me was why atmospheric born moisture did not form ice in the evaporating tunnels where fuel injection was spraying the fuel.
The refridgerating effect of the vaporising fuel would be identical there."

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There are no venturis in a fuel injection system. Heat in the cylinder is not a factor.

Partially incorrect. The ambient heat from the cylinder warms the intake manifold, and keeps fuel and water from collecting on the manifold. The venturi and the throttle plate tend to freeze in carb engines not only because of the temperature drop from pressure changes, but also because of fuel vaporization taking up significant latent heat before the throttle valve. Ice can still form around the throttle butterfly valve in injected engines at very low operation (idle) during descent (where high cooling air flow and very restricted throttle creates a mini-venturi near the throttle plate), but without the fuel vaporization, it is extremely rare and just not worth worrying about, and is fixed by just opening throttle.

 

Fuel injection is located near the intake for a few reasons: intake valve cooling, per-cylinder fuel air mixture control (dynamic control with o2 sensors), and, as a side effect, ice control. If you injected fuel upstream of the throttle valve, you would have much of the same ice problems as carbs.

 

Reverse-flow turbine engines, such as the PT-6, have to have a heating system for not just the air intake, but also in the cowling because of ice formation during icing conditions. Ice collects in the bend of the first intake stage where the air reverses into the compressor section.

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Just another data point on carb ice, dew point, alcohol, and the 912... Interesting to say the least.

 

A direct quote from: http://www.rotaryforum.com/forum/showthread.php?t=32058

 

"Somrthing worthy of noting is a lots of times the moisture is in your fuel.

I well remember in northern alberta canada being in a service trruck that could barely run in-40 temps because of ice buildup in the venturi.

I had to remove the air breather and chip the ice away with a screwdriver in the venturi before moving on.

There is not much humidity in -40 air so it had to be in the fuel itself.

I blame that on how much gas line deicer (alcohol) is added into our fuel to make up for how much water is actually in it.

If I was to fill my paint sprayer half full of alcohol and then add a half of cup of water to it it would all mix.

I could even put some gasoline in with that and it would mix as well.

If I then took that same spraygun outside and sprayed that mixture against a piece of cold metal a snow cone would start to appear.

The water portion of the solution would freeze against the metal but the gas and alcohol parts would evaporate away!

You could use your favorite whiskey for this same test but that would be alcohol abuselol.gif

One thing that always puzzled me was why atmospheric born moisture did not form ice in the evaporating tunnels where fuel injection was spraying the fuel.

The refridgerating effect of the vaporising fuel would be identical there."

Quoted sections like this by there very nature carry the implication of the endorsement of the poster and the validity of the information. I read the entire thread. This is one man's opinion. I'd like to see some Rotax and Bing engineer papers on this topic. That would have more credibility to me.
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Partially incorrect. The ambient heat from the cylinder warms the intake manifold, and keeps fuel and water from collecting on the manifold. The venturi and the throttle plate tend to freeze in carb engines not only because of the temperature drop from pressure changes, but also because of fuel vaporization taking up significant latent heat before the throttle valve. Ice can still form around the throttle butterfly valve in injected engines at very low operation (idle) during descent (where high cooling air flow and very restricted throttle creates a mini-venturi near the throttle plate), but without the fuel vaporization, it is extremely rare and just not worth worrying about, and is fixed by just opening throttle.

Fuel injection is located near the intake for a few reasons: intake valve cooling, per-cylinder fuel air mixture control (dynamic control with o2 sensors), and, as a side effect, ice control. If you injected fuel upstream of the throttle valve, you would have much of the same ice problems as carbs.

Reverse-flow turbine engines, such as the PT-6, have to have a heating system for not just the air intake, but also in the cowling because of ice formation during icing conditions. Ice collects in the bend of the first intake stage where the air reverses into the compressor section.

 

+1

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