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

Jeff Spitzer wrote:

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

That's the only way we ran it so I can't say.  We had two theories about
injectors.  Either do something to insure good distibution and atomizing in
the tubes or aim for the rotor face.  The normal way of installing
injectors at an angle to the pipe always has some of the fuel impacting the
far side of the tube and dribbling on down.  If the pipe is long enough
maybe it still evaps before the port.  Better to spray right in the end
(and far upstream of a bend) so that the fuel never hits a wall or turn
before evap is complete.  One must remember that what comes out of
injectors is droplets and it takes a finite time for droplets to evaporate.
 The theory of aim for the rotor face is identical to "port injection" cars
that aim for the back of the intake valve.  If the droplets hit a hot
surface they vaporize almost immediately and mixing of the vapors can take
place in the turbulence in the chamber.

Jeff Spitzer

You saw the holes that Jim used in the rotor housings. To be
at the right angle to hit the hot rotor they would have to be further 
around on the housing about where the oil injectors are or even further. 
That might require higher fuel system pressure because compression may be 
starting. 

Heard anything about the high pressure fuel injection Fisch 
system used on the OMC outboards lately?
 
Paul Lamar
 
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