[Diy_efi] WBO2 and AFR

[gary]

----- Original Message ----- 
From: "Michael Richards" <michael at fastmail.ca>
To: <diy_efi at diy-efi.org>
Sent: Friday, July 08, 2005 10:53 AM
Subject: Re: [Diy_efi] WBO2 and AFR


> I neglected to cover the point past which the wideband controller 
> begins to use it's HC part of the sensor to determine how "rich" 
> the mixture was. 

At the risk of sounding as an infallible expert, WBO2s measure
the oxygen (actually the partial pressure of oxygen) content in the
exhaust stream. Most sensor meters/controllers (analog) utilize
the pump cell current generated (steps/descriptions in between, 
have been omitted to limit content of post) to determine number
chosen from a lambda lookup table.  This is/can be converted to
a AFR number.  The sensor recognizes only oxygen.  No other 
aspect of the exhaust content is recognized.  They are referred
to as OXYGEN (and oxygen only) sensors for a reason.    
>
> Point I was trying to make is that oxygen rendered by the 
> combustion, for example in oxygenated fuels ought to be 
> cancelled out in the equation. 

This is where the actual number recognized as 'stoich' can play in.
> 
> Correct me if I'm wrong but widebands measure the lambda and 
> mathematically convert the result to AFR. I primarily tune with 
> AFR only because that's what most people understand. 

Well, if you are implying measure of oxygen, which then ends up
at a lambda lookup table.... then yes.  If not, see above. 

I subscribe to diplomacy.  Tune in lambda, then communicate 
with customer in AFR.  Communcate with a German, in a 
language they understand.... German.  Hmmm, didn't realize I
was bilingual.  :)    
> 
> I feel like those who stick their noses up and point at the lambda 
> difference are the same group who will correct one calling a 
> recirculating valve a BOV. Both issues they are technically correct 
> but neither makes the customer feel good about themselves as they 
> discuss the setup with the tuner.
> 
> So in a sense I think that those of us who use the AFR numbers 
> are actually using lambda but not realising it. 

"... those of us who use the AFR..."  Maybe indirectly, to be 
optimistic about it, with conversion already done for you.  :)  
I compare that to english/metric measurement.  Both determine 
same thing, but each is separate.  Either can be converted, but 
they are different from one another.  Are you using metric, when 
someone has previously converted it to english for you?
> 
> Thoughts anyone?
> -Michael
> 
> >>> Would you not consider a stoich mixture of fuel one
> >>> that consumes all the available oxygen?
> > 
> > A guarded No.  The reason being stoich implies burning the available
> > fuel AND oxygen present.  You can burn whatever available oxygen
> > there is, but still have left over fuel looking for their share of
> > oxygen molecules.    Still not stoich, but in lieu of above, I prefer
> > to state mixture as one that burns what ever fuel is available.
> > 
> > 14.7 was chosen as stoich, as this results in the least amount of the
> > various components/products of combustion recognized as harmful.
> > IOW, a compromise.