[Diy_efi] Donegan ECU

[Carter Shore]

I think the most important justification for ECU
control of the fuel pressure is to extend the dynamic
range of the injectors on the low side, not the high
side.
The time required to open and close elctromagnetic
injectors is determined mainly by the injector design,
and the supply voltage. 
At very low duty cycles, even P&H injectors have
difficulty delivering a consistent amount of fuel.
But if you lower the pressure, then you can use a
longer pulsewidth to deliver the required amount of
fuel, mitigating the issue.
The same square-root relationship between pressure and
flow that makes it harder to increase the flow by
increasing the pressure, works to our advantage when
reducing the pressure to deliver accurate fuel on the
low end.
Of course, there are limits to how far the pressure
should be reduced, that depend on the specific
injector.
But reducing the pressure by just 10% yields nearly
20% reduction in flow, corresponding to a 20% increase
in injector 'open-time', ie a longer pulsewidth.

This isn't that much of an issue for racecars, but
streetcars must idle, and pass emissions tests.

Carter Shore 


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com