[Diy_efi] Donegan ECU

[Bernd Felsche]

On Friday 05 January 2007 00:57, Steven P. Donegan wrote:
> I had not thought of fuel temp at all - every vehicle I drive
> would consume the gas in the rails well before it got warm :-)
> However this does raise a point - perhaps my ECM/PCM/EFI computer
> needs a way to open a fuel return line and to sense fuel temp in
> the rails? Any ideas on how useful that would be in the 'real
> world' anyone?

Superflous if you're running in closed-loop; which you would be if
the fuel rail was warm enough to make a difference.

If the temperature in the fuel rail is a problem, then a
recirculating fuel pressure control system is IMNHSO a better
solution. In such a system, there's always "fresh" fuel that's in
excess to the amount required for injection from the tank flushing
the rail(s). The fuel tank is the cooling environment for the fuel.

Pressure regulation also happens at the rail(s), whereas in
"dead-end" systems it's at the fuel pump, perhaps a several metres
from the rail and therefore the injectors. That increases the
difficulty in controlling the pressure (time delays that depend on
fuel pressure and temperature); especially if it's to vary
dynamically wrt manifold pressure.

The ability to vary the fuel rail pressure is at least desirable to
get consistent injected quantities due to a fairly constant pressure
difference across the injector; between the fuel rail and the
manifold where it's injecting.  Makes for simpler calculations on
injected quantity.

If you're stuck with a "dead-end" fuel delivery system, then you
need to add a return line and a valve that vents the rail(s) back to
the tank in the interval between the fuel pump running and the
engine actually being started. The time delay will depend largely on
the free-delivery rate of the fuel pump and the volume of the fuel
rail(s). That ensures that there's "cold" fuel in the rail(s) before
you start injecting it.

-- 
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