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Re: [FlyRotary] Re: Fuel Injector Sizing
Depends on the type of pressure regulator.
The concept of a manifold-referenced pressure regulator is to keep the pressure
differential between the pressure of the fuel and the pressure of the manifold a
constant. That way the injectors see the same pressure differential at all
times and inject the same amount of fuel for the same duration open
time.
If the pressure regulator does not
compensate for the difference, then when the fuel pressure is 40 psi and the
throttle wide open the difference would be (approx) 40 - 14.7 (at sea
level standard day) = 25.3 psi. Then if you close the throttle and
manifold pressure drops to - say 7.7 psi then the difference would be 40 - 7.7 =
32.3 psi. So there would be a 7.7 psi increase in
pressure across the injectors and more fuel would be injected for the same
duration signal. So in this example the manifold-referenced fuel pressure
regulator should sense the manifold pressure and
reduce the fuel pressure by 7 psi down to 32.3
psi. Then the difference 32.3 - 7 = 25.3 psi and the injectors see
the same pressure differential at both throttle settings and injects the same
amount of fuel for the same duration in both cases for steadier
performance.
If that understanding is correct then it would seem
to imply you should see the fuel pressure gauge reacting to major changes in
manifold pressure (say from WOT to idle) without a problem. If the
pressure regulator was not manifold-referenced then, the fuel pressure would be
maintain at some constant pressure without regard to maintaining the pressure
differential across the injectors and you would see a steady fuel gauge
needle.
At least, that is my understanding of
it.
Ed A
----- Original Message -----
Sent: Saturday, January 22, 2005 10:21
AM
Subject: [FlyRotary] Re:
Manifold-Reference Fuel Pressure was [FlyRotary]Re: Fuel Injector Sizing
Ain't that what they are supposed to do ?
Keep it steady as outside pressure diminishes ? Doesn't your gauge suffer from
the same diminishing outside pressure as altitude increases; therefore,
wouldn't they stay constant, if working properly ? 'Splain to us simple
minded, of which I may be the only one.
jofarr
I agree with your statement, Buly.
Ideally if the pressure differential between fuel rail and manifold is
kept constant by use of a manifold reference then that would imply that the
fuel pressure should vary to compensate for different manifold
pressure. However, my fuel pressure is rock steady and this is the
second manifold-referenced fuel pressure regulator I have used with no
difference. So either my manifold-reference fuel pressure regulator
isn't or I am misunderstanding what they are suppose to do.
But, that is my experience. How about
others of you flying what is your experience with fuel pressure???
Does it vary? The variance corresponds to what??
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