[Diy_efi] WB O2 system

[Garfield Willis]

On 19 Jun 2002 21:21:10 -0000, "Tom Sharpe" <twsharpe at webmail1.mtco.com>
wrote:

>Will a NB sensor side by side with=20
>a WB tell is where stoich is???  If so, we might be able to guestimate =
10%=20
>rich (or lean).  I'm talking relative here.  We still need a dyno to get=
=20
>the 'best' numbers.   TomS

Uhhh, I think I see from whence the confusion here. When I said you
might be lean when your meter indicates rich, I meant relatively
leaner/richer, compared with petrol AFR readings. I did NOT mean your
instrument might read rich of *stoich* when you're actually lean of
stoich; that would mean stoich itself had shifted, which thankfully
doesn't happen with these sensors. If your idea above is expressing the
concern that you need 'another sensor' to even find where stoich is,
nope not necessary.

Here's my quote verbatim:
>It's conceivable that with
>the right mix of additives, you could actually BE leaner, while your
>petrol-calibrated sensor/meter INDICATES 'richer'.

Note the 'er' part, eh? What I was trying to say is, you add something
to your petrol, and your petrol-calibrated AFR meter says "richer". BUT
it could in fact be "leaner" in actual AFRs. That's because fuels,
oxygenates, and diluents can pull the readings (produce sensor
artifacts) in opposite directions; the net effect ("richer" or "leaner")
depends on the proportions of each additive, AND which side of stoich
you're on, too.

BUT, Neither a NB nor a WB sensor has any trouble finding stoich itself,
regardless of fuel, oxygenates, or diluents (like water vapor or
nitrogen). It's the point of chemical inertness of the exhaust gases,
sotaspeak, so no, you don't need another sensor along side. THE problem
is what happens when you move *away* from (either rich or lean) of
stoich, and you're not using straight petrol. It's not the stoich
reference that shifts around, it's the AFR vrs. Ip (oxy pump current)
relationship that changes; no NB will help you compensate for that.

BTW, you don't need a dyno to get horse-shoe close to mixture sweetspots
for various fuels. Once properly corrected for the fuel, any decent AFR
meter should be able to get you within 0.2AFR of target. The issue is,
(1) what are those sweetspots roughly, for your particular fuel and
engine type, so you can be sure you're starting out safely within the
locus of hocus pocus, and (2) what should your petrol-calibrated AFR
meter (if that's all you have) be reading, when it's near that sweetspot
with your particular fuel. Ray Hall and others have posted on the web
some tips on what racers have found are good starting points for tuning
with alternate fuels. But those AFR numbers were developed long ago
using the 'direct method', so they're *actual* AFRs, which is again why
we need to correct our sensors/meters if we want to make sense of these
numbers, develop and communicate our own results (especially important
in the case of water injection, which is in need of resurrection), so
others can use them, understand them.

Itinerant Sidebar:
The whole silly oversimplified mantra of "give her what she wants" (and
therefore, "we don't need no stinkin akurcy") would obviously be 'fine',
if you could *first* get close enough to "what she wants" that you don't
kill her in the process of trying to please her. Without decent
accuracy, and especially without correction for major fuel changes like
alcohol and/or water injection, it's like pouring various concentrations
of rubbing alcohol on your sweetie, and asking her if any of them smell
like perfume to her. Trying to "give your engine what it wants" when
you're potentially *miles* off from at least a SAFE mixture, is one hell
of a way of trying to 'make your engine happy'. Yeah, by all means "give
her what she wants", but at least start out knowing roughly where you
are. You need decent accuracy for this. In the case of petrol alone,
being at 13.5AFR when your meter says you're at 12.5AFR is an example of
being miles off, not even close to perfume. Even being off as little as
0.5AFR when nearing peak power can mean the difference between
'intonation' and detonation. :)  ANY decent professionally
designed/built AFR meter, and with at least proper hand-calc corrections
if you're using fuel admixtures, can get you good enough results that
you can safely avoid these dangers, and creep up on your "best numbers"
from the safe side, instead of killing your precious off trying to
"please her" in the dark. And have something useful you can contribute
and communicate to others doing same. You don't really *need* a dyno for
this, it just speeds things up. But you SURE don't want to mistakenly
creep up on your 'best numbers' from the leaner direction.

Besides, most women (and engines) naturally prefer being approached from
the rich side. Heh. A modified and workable mantra might be, "ask (start
from known sweetspots) what most engines (women) want, so you're at
least close; then start there in trying to give her what she wants". I
believe this has proven to work with most, umm, engines. :)

HTH,

Gar
Gar Willis
Principal Engineer
EGOR Techno
3491 Edison Way
Menlo Park, CA 94025
650-216-9874
garwillis at msn.com (e-mail & PayPal transfers)
www.egortech.com (best viewed with IE)


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