Re: Question about "higher flow" injectors

[Orin Eman <orin@WOLFENET.com>]

> Now what is the "spring" in the CIS system?  These old systems use
> hydraulic pressure in the form of gasoline to provide the spring, with 
> the various pressures and contollers providing the "spring rate".

> This leads me to believe that an adjustment to the system pressure and/or
> control pressure will allow the larger injectors to be used.  Caveot...
> I HAVE NOT DONE THIS, and have not figured out the details.
> Anyone who cares to pitch in their BTDT is now welcome to...

No BTDT, but some observations.  Firstly, the flow thru the injector
is determined by the pressure drop in the fuel distributor and the
size of the slit up to the point at which the injector itself becomes
the major restriction and can't flow any more.
The size of the slit is determined by the position of the plate in the cone.
The position of the plate is determined by the amount of air flowing
past it and the control pressure - lower control pressure means the
plate is higher for a given air flow and a greater fuel flow.  The max
fuel flow is still limited by the maximum size of the slit, so
just changing control pressure won't help.
Lastly, we have the pressure drop across the slit.  THIS is what we
can play with.  In the turbo motors, it is controlled by a frequency
valve - you are supposed to set the fuel distributor up such that
the duty cycle of this FV is 50%...  Set it higher and the pressures
change such that more fuel goes to the injectors, lower and less fuel.
(Normally, the computer uses the O2 sensor to set this duty cycle.)
However, in the ECU are some tables of duty cycles to use under boost.
These max out at around 70%... there is an absolute maximum imposed
of 95%.

So, for those RPM ranges where we run short of fuel, we can increase
the duty cycle for a greater fuel flow.  On top of that, we could
increase control pressure along with an across the board increase
in duty cycle... this would prevent the plate rising as much for
a given amount of air flow, but the fuel rate would be increase
to the original by the increased duty cycle.

Orin.



> paul timmerman