Fuel Atomisation

[Bernd Felsche]

Bruce tapped away at the keyboard with:

> From: "Bob - Uni" <rcs07 at uow.edu.au>
> > Is that why bigger injectors that flow higher but dont atomise as well
> > tend to rob you of idle quality and low down power? Would it be better
> > then to have two smaller injectors per cylinder than one bigger one?

> If you were to look at some high speed photos of an injector
> firing, you'd see how the piddle and drip as flow starts, the
> large the injector the worse the problem.

For about 50 microseconds; but depends on injector, injector
pressure and issues such as air shrouding.

> Also, any the actual injector on time cal'c becomes more critical.
> Once you get down in the region of a 1 msec PW, some injectors
> just become non linear in fuel vs time, and the inertia of the
> guts of the injector become a limiting factor in how fast the
> injector can open and close.

Doesn't matter that the behaviour is non-linear. As long as the
non-linear behaviour is known, the ECU can compensate accordingly.
e.g. The EFI332 project makes allowances for non-linear injector
behaviour, IIRC.

> The longer the *on* time the more accurate you can be in how much
> fuel gets metered in a given cycle.  At a 600 rpm idle you have
> 100 msec between ignition events,  or roughly 75 msec to spray the
> back of the valve, rather then use a 2 msec time, with convential
> batch fire system if you used more of the time availble the better
> you'd be.

At least some batch-fire systems only fire once every two revs at idle.
Doing so under light load at low, off-idle speeds should be feasible if
the inlet manifold and and ignition timing allowed for asymetric
fuelling. I don't know if it's been done; there's little point in
developing such a system now that sequential injection is the rule.

> It would be interesting to play with a system that offered a huge
> turn down ratio so you had some huge amount of injector on time at
> idle, and then decreased to a smaller value as rpm rose.
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