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Subject: RE: [FlyRotary] Re: Fuel System Design - Jet Pump
Date: Wed, 16 Feb 2005 14:03:34 -0600
Message-ID: <87DBA06C9A5CB84B80439BA09D86E69EC07F72@MAIL01.austin.utexas.edu>
Thread-Topic: [FlyRotary] Re: Fuel System Design - Jet Pump
Thread-Index: AcUUYDd38j29EchiTo20+ik89dpGMQAAE38w
From: "Mark R Steitle" <mark.steitle@austin.utexas.edu>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>

Ernest,=20
First, I think I'll defer all your questions concerning MAP and throttle
positions to Tracy or Ed.  I know that you can have WOT at low rpm that
requires a different amount of fuel as WOT at high rpm.  Engine loads
has a lot to do with things, hence the MAP port to the EC-2.  The EC-2
instructions clearly state not to attempt adjusting a/f ratios without a
prop, or some means to load the engine.  To do so is a waste of time...
makes sense. =20

One thing I did learn from the referenced efi article is that auto
manufacturers went to returnless efi systems for emissions reasons (hot
fuel splashing into a partially full fuel tank causes vapors that can
end up as smog).  The returnless systems run higher fuel pressures (65
psi) to keep the fuel from boiling in the fuel rails and lines.
Personally, 38psi is too high for my personal comfort, but that's the
nature of fuel injection.  The homebuilders seem to like the returnless
systems for the simplicity of the design and to get around having to
purchase a $500 fuel selector valve.  My kit came with the Andair dual
selector valve, so that decision was already made for me.  Tracy seems
to have a good solution to that problem.  I would probably copy his
design if I didn't already have a selector valve. =20

Mark S.


I'm still wondering how important that pressure is.

First, didn't we learn earlier that the flow doesn't vary linearly with=20
the pressure differential; that it take a lot more pressure to get a=20
significant difference in flow? This would tend to limit the effect of=20
MAP changes. Referencing somewhere other than MAP will make a=20
difference, just not a whole lot. Would this be a reason that all of the

returnless systems are running at higher pressures? Say the MAP varies=20
15", there's less percentage difference between 30"->45" than there is=20
45"->60". That keeps you in the ballpark. The ECM takes up the rest of=20
the slack.

Then there is the fact that Ed has flown at least a couple hours with a=20
system that was not referenced to MAP. The original problems were tuned
out.

Leon, I'm not claiming to know anything. Shoot, I'm still a month away=20
from STARTING my first engine rebuild. But it just seems to me that with

an atmospheric controlled regulator, all that you would need would be a=20
throttle position sensor to know how much fuel to dump in the intake.=20
The regulator will relax the pressure as you climb to lean the mixture.=20
And except for barometric difference, the MAP will always be tied to the

throttle position. Now all you need is a fuel map that says how much=20
fuel to use at each throttle position. I'm sure I'm missing something,=20
and I'm sure it's not the sort of thing you find in textbooks.

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