pulse width / pulse granularity

[Carter Shore]

Hello DIY LM's,
When I first connected a scope to my injectors, I was
surprised that the actual pulsewidth did not increase
linearly with RPM/load, even at WOT. Slowing down the
sweep showed me why: The amount of fuel injected is
proportional to the duty cycle, not the pulsewidth. 
A (very) broad generalization is that the difference
in pulsewidth is due to differences in VE, not engine
speed. This, because the amount of fuel needed is
approximately proportional to the amount of air that
the motor breathes at a given RPM (ie VE).
Of course, at the extremes, as the duty cycle
approaches 0% and 100%, this generalization falls down
due to the physical limitations of the injectors.

My point being that the most sensitive AFR tuning
requirements for emissions occurs at lower RPM (non
WOT operation). And since the pulsewidth will be on
the shorter end, then finer timeslice resolution would
be a good thing. 

Now, does anyone know how much 'jitter' an injector
typically shows on delivered mass of fuel vs
pulsewith?
Of course in closed loop mode any non-linearity is
compensated for, but the 'jitter' in such a closed
loop system will show up as noise, and can cause loop
stability problems, etc.

Just wondering

Carter Shore

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