Electric Fuel Pumps

[Greg Hermann]

>Hi Greg,
>    The controller I was using was an Autronics box....it has no feedback to
>watch fuel pressure and adjust PW...The fuel pressure drop has always
>happened on the Blown alcohol datalog stuff I have looked at when shifting
>gears, and I noticed the rise in AFR upon full throttle shift when I was
>datalogging this but was only about 3/4 of an AFR on the Horiba and if my
>memory serves me was about .4 seconds....but, when it would almost stall on
>upshifts rpm had dropped about 2000 whereas full throttle was only around
>800...my guestimation on what happens is the pump is pumping 100gph(for a
>number) and immediately changes to 80(for a number) it produces a mass
>volume hole that the bypassing regulator on the end of the rail could not
>react fast enough to...I don't know the physics of why...I just saw it and
>can't see how it could have been cavitation if it would accelerate fine
>without a gear(RPM) change....someone on this list should be able to
>enlighten us though...(I bet it'll be you Greg after you think about it a
>while, I've seen you come up with some pretty brilliant stuff)  ttyl
>-Carl Summers
>

(Blushing now!)

Well--control valve sizing is an interesting ART, that's for sure. Bigger
is _DEFINITELY_ NOT_ better! And I'm kind of inclined to think that you
could need a rather differently sized relief valve port with a mechanically
driven pump, on account of having the pump volume adjust automatically for
engine speed-- Have to play with some numbers and see what flow rates are
needed under various operating conditions.

Also, Would be inclined to think in terms of putting the relief valve LOW
on the rails, so it ALWAYS sees liquid, never vapor. Again--to keep it more
consistent. Lots of difference between how much volume of vapor will flow
through a relief port and how much volume of liquid at same pressure delta.
Idea is to minimize the amount of motion the valve plug has to do to keep
thing right. A properly "characterized" valve plug is pretty important too.

Already fising to put a bleed orifice--or a float vent--at the high
point(s) of the rails to take care of the vapor--instead of putting the
relief valve high.

Will ponder on this one a bit, for sure! This problem is not too different
from getting a waste gate to do what you want in terms of controlling
boost---

Greg


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