RE return to fuel tank

[Greg Hermann]

>Greg Hermann wrote:
>
>> The most stable fuel pressure control will be possible if you use a
>> variable drive fuel pump,  a pressure regulator,  feedback on what the
>> regulator is doing from a fuel pressure transducer, and a controlled
>> reference pressure on the back side of the fuel pressure regulator
>> diaphram, as well as a fuel temperature transducer to allow proper
>> correction for fuel density.
>
>It's a little easier to do, measure the pressure and temp in the fuel rails and
>just bleed a very small amount of fuel back to the tank (vent the tank into the
>air cleaner) and control the pressure with the pump (ECU).
>
>Regards  Tom

You are right, the return bleed flow does not have to be all that big, but
I DO think that the regulator has got to be the lead control in the loop
for best stability. Let the pump follow the regulator so as to try to
maintain aa near as possible to a constant return flow, so that the
armature in the regulator is not needing to jump around all the time. Gets
you to the same place, but with more stability in the loop. The controlled
pressure on the back side of the regulator diaphram is what would give the
computer an active input into what the regulator is doing. The voltage
control to the pump gives it a second active input. The two active inputs,
properly coordinated, is what will give the truly stable control.

Without getting into another whole thread on control theory at this point,
let's just say that a control valve needs to present a minimum of about 25%
of the flow restriction in a given flow circuit when wide open in order to
be able to do a decent job of controling flow in the circuit over a wide
range---and if you can use subordinate controls to minimize the amount that
the primary control has to stroke through its range, you will get a MUCH
more  stable controlled variable.

REALLY WAY OFF SUBJECT:

In my mind, one of the neatest things that the development of digital
technology has accomplished to date is to bring the cost of sensors,
transducers, operators and the means to read them and tell them (logically)
what to do down to a level where it is now economically realistic to try to
apply control techniques and theories that used to only be economically
justifiable for huge industrial plants to hobby level projects. The use of
such stuff will literally explode as soon as just a few more people learn
how to use the new capabilities.

For example: I was pondering the other day on whether anyone has thought to
apply a HEGO sensor to a domestic hot water boiler or furnace so as to hold
it at (or pretty near) stoich mixture, rather than pretty far lean, as is
now done to be on the safe side with varying operating conditions and the
like. Even the highest efficiency units could gain another point or three
of efficiency by doing this---

Regards, Greg