Carb icing is caused by the pressure drop in the venturi
& the simultaneous evaporation of the fuel.  I doubt that the
fuel evap alone will cause any ice, and there is no significant
pressure drop in the straight manifold.

Bill
Long EZ builder & pilot
mechanical engineer

Jeff Spitzer wrote:

Yes and no.  The situation is definately worse in the carb.  But we would
regularly ice up the *outside* of our intake pipes on the dyno at Moller
when we were injecting at the inlet end.  The math is rather simple.  Just
use the heat of vaporization of the fuel and F/A ratio.  I did this once a
long time ago and decided that indeed it is easy to pull enough heat to
form ice.  BTW, I NEVER saw ice on the inside of the tubes.

Jeff Spitzer

We could use a little ice in the engine compartment to cool things off.
Did the engine make more power Jeff with the injectors out there?
Higher charge density?

We could wrap copper tubing around the intake tubes and use
it to cool the oil.

Paul Lamar

Hi Jeff,

Did you see the Packard diesel explanation?  I agree that there
is plenty of cooling going on, but with a smooth pipe there should
be no real problem with icing in the sense of obstruction the
airflow and causing power losses - which is what I was referring
to in the previous comment.   As to Paul's idea, "sure" - but
of course we are back to 'you can't get something for nothing'
and the warmed air will be less dense and will cause a power
loss.  How much depends on how hot you heat it.
This is why Gary Hertzler built his own sump for his Lyc
in his ultra efficient Vari-Eze - he just couldn't stand to
heat up his air on the way thru the sump.  He has a seperate
intake manifold like a Continental to avoid the power loss
from heating the air.  OTOH, the net thermal efficiency
should be up due to recycling some of the waste heat.
Regenerators, anyone?

Bill
Long EZ builder & pilot
mechanical engineer

I have always wondered about that heat recycle Bill. Would it not be
better to warm the air once it was trapped in the compression
chamber. I would guess there is no benefit until you get the mass
of air into something that will contain the expansion.

IMHO One of the reason Lycoming does the intake-manifold-through
-the-oil-sump trick is to even out the fuel distribution from
the carb. Icing is another of course. Makes no sense with fuel injection.
 
Paul Lamar
 
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