[Diy_efi] injecting 5 port head

[Jean Belanger]

--- Adam Wade wrote:
> 
> --- Jean Belanger wrote:
> 
> > If you only inject when the intake valves are open
> > then the fuel will be carried to the right cylinder.
> 
> I think you are forgetting that the intake openings of
> the cylinders sharing the siamesed port overlap each
> other, so unfortunately it's not nearly as simple as
> you appear to be claiming.  You might be able to
> manage with a single injector, but I would wager it
> would be easier to implement with multiple injectors.

I was not forgetting that, I was just simplifying things for a general
explanation. As for making it easier with multiple injectors, Rover did not
seem to think so when they made the MPi Mini. They only use a single
injector per port.

You should have a look at the Rover patent because they describe 2 modes of
operation. One mode is the obvious pulse on an open valve and the second is
a single pulse which starts when the number 2 (or 3) cylinder valve is open
and finishes when the number 1 (or 4) cylinder valve is open covering the
overlap region. I don't know if the MPi engine uses them both but it seems
the best way to go to high RPM and still have a reasonable size injector
without worrying about the time needed to open and close the injector during
the intake overlap. I assume that this mode also requires a cam which does
not have an excessive amount of overlap between intake and exhaust otherwise
you'd be injecting fuel out the exhaust.

> In particular, as I understand it, you cannot inject
> fuel prior to the closing of the "inside" cylinder's
> intake valve and have any of that fuel end up in the
> "outside" cylinder -- for cylinders 2 and 3, you are
> limited to the time between the closing of the #2/3
> intake valve and the closing of the #1/4 intake valve,
> which is a pretty short period, especially at higher
> rpms.  In fact, you posted the link to the info on
> this just the other day!  His site has been moved,
> though.
> http://www.shell-4000-rally.org/starchak/efi/siamese.htm

This is true for discrete injection pulse per cylinder but with the mode
described above it is no longer true if you time the pulse correctly (which
has to be done anyway). During the intake overlap, some fuel will go to both
cylinders but the amount to each should be similar from cycle to cycle. So
you just need to time the injection pulse to get a constant AFR between the
cylinder pair.

> 
> I think a staged injector system might be in order
> here; in fact, it's possible that the optimal
> combination would be a single sat. drive injector for
> cylinders 2 and 3 (since you can inject fuel starting
> when the "outer" cylinder closes its intake valve, you
> have a decent amount of time to allow injection of
> sufficient fuel volume before the "inner" cylinder
> opens its intake valve, even with a smallish sat.
> drive injector), and staged dual injectors for
> cylinders 1 and 4, which would allow a honkin' big
> injector for higher-load running and a small injector
> to handle idle control.

And this is simpler than one injector per port? It seems quite complex for
both hardware and software.

I agree that staged injectors are a good way to have a better dynamic range
and it's going to be an option with the code I'm writing. This is almost
essential for turbo engines which require quite big injectors for top end
power but would have problems idling with those. But for this staging you
only need 2 injectors per port not the 3 you're suggesting (or is it 5
total?).

> Timing the injection on the
> center pair of cylinders will be critical.

I agree that timing is critical but it's for the outside cylinders. They're
the ones with the smaller injection window.

Jean
 

-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.409 / Virus Database: 268.15.28/604 - Release Date: 26/12/2006