[Diy_efi] Interesting AFR sensing idea

[Eric Byrd]

Theoretically it seems straightforward to make a system that will guess
this on its own, and correct itself.  In closed loop, just before each
rich pulse, you know the mix is close to stoich.  You could take a plug
reading at this moment, and average several hundred readings, and know
this voltage corresponds to stoich.  In open loop, you could tap the fuel
map value, compute fuel mass in the charge according to injector flow
rate, which stays pretty constant, compute a corresponding rough AF value
with MAP/IAT/RPM/VE or MAF, and match these values over a decent sample
with the plug voltages.

But in practice, I would wager the plug voltage doesn't just vary with
mix.  I bet it also varies with charge temp, density, and who knows what
other variables that affect the resistance of the gap.

Still, if you had another way to measure AF, you could use those values
to calibrate your plug voltage system, and then you would have a good AF
measurement that was much faster than the one you started with.  But as
you pointed out, this curve is probably unique to this motor and setup.

Eric 

On Wed, 27 Nov 2002 01:31:49 -0800 Perry Harrington <pedward at apsoft.com>
writes:
> I was looking through some scope traces and explanations here:
> http://www.cnnw.net/~fourty/trendingdis.htm
> 
> And something occurred to me.
> 
> Would it be possible to detect precise AFR readings based on the 
> firing voltage
> of a cylinder's spark?
> 
> If the voltage is higher the cylinder is lean, lower and it's rich.
> 
> The real issue is determining the relationship between AFR and 
> voltage.  Since
> engine's vary and their spark systems do too.
> 
> --Perry
> 
> -- 
> Perry Harrington			Data Acquisition & 
> Instrumentation, Inc	
> perry at dainst dot com					 
> http://www.dainst.com/
> 
> Those who would give up essential liberty to purchase a little 
> temporary safety
> deserve neither liberty or safety. Nor, are they likely to end up 
> with either.
>                              -- Benjamin Franklin
> 
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
> http://www.diy-efi.org/mailman/listinfo/diy_efi
> 


________________________________________________________________
Sign Up for Juno Platinum Internet Access Today
Only $9.95 per month!
Visit www.juno.com

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi