New member - Aircraft engine EFI

[Bernd Felsche]

Bruce tapped away at the keyboard with:
>----- Original Message -----
>From: "Bernd Felsche" <bernie at innovative.iinet.net.au>

>>Bruce tapped away at the keyboard with:
>>>From: "Bernd Felsche" <bernie at innovative.iinet.net.au>
>>>>Bruce tapped away at the keyboard with:
>>>>>From: "Jeremy Harris" <Jeremy at UKPilots.net>
>>>>>>My reasoning for EFI has more to do with weight
>>>>>>and freedom from icing than fuelling accuracy.
>>>>>Given the right conditions EFI can Ice up like a carbbie.
>>>>>Many throttle bodies include an coolant transfer port to
>>>>>prevent this.

>>>>Yep. Happens at near-freezing temperatures with high moisture
>>>>content in the air. Fortunately, he's got an air-cooled engine
>>>>to use for pre-heating the air.

>>>Shame to have to heat the whole intake tract using that method.
>>>Mabe circulate some engine, reduction gear box, oil thru the
>>>throttle bodies.

>>I'm not sure all that much oil cooling takes place in a BMW engine.

Should have said I don't know _if_ that much takes place. I was
never allowed to dismantle one on display. :-)

>>Porsche engines have been oil-cooled since about the 911.

>>You don't have to take all the inlet air from the cooling air exit.
>>You mix just enough to read a temperature of about 25 degrees C
>>which is "ideal" for vapourization anyway.

>>One could go to a junk yard and get a preheat thermostat with
>>control flap from a watercooled VW's airbox and hook them up to the
>>manifold side of the throttle valve for vacuum. The thermostat is
>>set to open the flap control below 30 degrees C, fully open at about
>>18 degrees C. It's extra mass on an aircraft (though probably less
>>than 250g for the components, but perhaps double that again for
>>ducting and housing), which is why I didn't mention it before.

>KISS sure falls apart with your strategy.

It's simple stuff, but another two (albeit simple) gadgets that can
go wrong.  A manually-controlled flap can be "forgotten". The
plumbing to a heated throttle-body can fail in a number of
non-obvious ways.

My initial recommendation was to show the pilot if the inlet was too
hot/cold and get the pilot to move the pre-heat flap. Inlet air
temperature is something the fuel injection really ought to know,
especially for restarts.

>Where does the 25dC ideal vaporization number come from?

Don't remember exactly. It's _about_ 25C. 27C was stated in some
(German) VW literature on the preheat function. No doubt this varies
with fuel type.  Another source could be Charles E. Probst's book on
Bosch FI, but could be in several others of the hundreds of
engineering books/articles in my library.

The temeperature is "ideal" in as much as preserving charge density
whilst ensuring good vapourization.

-- 
Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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