Alpha-N vs. Speed Density?

[Garfield Willis]

Looks like I typed this in, but never hit the send booton. Garputz


On Tue, 25 Jul 2000 12:49:45 -0500, steve ravet <sravet at arm.com> wrote:

>alpha-n is the most basic type of EFI, AFAIK only used on engines where
>you can't really measure MAP (throttle/cylinder, lots of overlap, etc.).

Nuther tiny addendum just for curiosity-sake, but Alpha-N fuel injection
is still in use on aircraft engines using the "Continental FI System",
admired for it's reliability and simplicity. Not admired so much for
it's 'easy' starting, tho.  :)

I know what was asked was "differences in strategy" or basically, what's
the differences in the algorithms, which others have already commented
on, but...

Also, since the chap was asking for "gimme the big picture", another
thing to observe is that strictly Alpha-N racing *systems* were/are
mostly used where the fuel delivery is "continuous" as in "continuous
fuel injection" vrs "pulsed fuel injection", the latter being the stuff
we all expect these days with modern EFI systems. So usually, Alpha-N
systems are systems that have a fuel metering device/pump/system that
controls a steady flow of fuel to "nozzles" at the cylinders, rather
than electrical solenoid operated "injectors". Maybe another way of
saying the above is that commercial Alpha-N systems are most often
*mechanical* fuel injection systems.

The taxonomy of fuel injection systems past and present is really pretty
broad and fascinating (wull, I think); you have MAF-based,
MAP-based/aka-SpeedDensity (by the way guys, does the direct
airflow-measuring based system - MAF - have another name similar to
"speed-density"?), and of course Alpha-N, as far as "fuel metering
algorithms" are concerned. Then there's the issue of whether the fuel
that's metered is delivered in a continously flowing stream thru a
"nozzle", which is referred to as continuous (or constant) fuel
injection or just CFI, OR whether the metered fuel is delivered in timed
squirts or pulses, AND add to this goulash, whether the pulsed squirts
of fuel are caused by an electrically operated solenoid (modern EFI
injectors) or a mechnically operated "squirt gun pump", ifyawill
(Lucas).

Commerical strictly Alpha-N racing systems are still built and sold by
folks like Kinsler, Hilborn, Enderle, and their info makes for some
interesting reading. [I used to have a Hilborn catalog around here
somewhere I can't put me fingers on right now, but their stuff looked
alot more like jewelry than auto parts, with beautifully shot glossy
photos, and myOmy was it ever pricey!]

OH, another thing somewhat off-point, but important as a "big picture
factoid": many(most?) modern EFI systems designed primarily to measure
air directly (MAF) or estimate indirectly (MAP-Speed Density), *will*
revert to an Alpha-N algorithm (using just the TPS-throttle position
sensor and RPM as secondary/backup inputs), IF the ECU thinks the
primary air sensor device (MAF or MAP) has failed.

Now, I must confess I'm an admirer and afficiando of all this old stuff,
but not much of an expert, so them's what knows these parts precisely,
please jump in with a correction or addition, cuz I'd like to know more
about this stuff, and get things hysterically straight as possible for
me own enjoyment.

Gar


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