ox sensor on sequential efi,high overlap cam.... a bit lo

[Jemison Richard]

The WWII FI birds (which often had some pretty wild camming to get the power
required) and supercharging, EGT was the indicator of choice for mixture
control but no one worried about it til you got up and pretty well
stabilized in cruise (or for the multiengine planes with a flight engineer,
had the engine up in the power range).   The wild cam basically says the
designer (and the user) don't really care about low end quality and are
willing to sacrifice it for upper rpm maximization of HP!

Lets try to little mental game playing here.  First assume it is possible to
control mixture with high overlap and low rpm.
If the engine is really setup well and the cam isn't too wild, you can
usually get them to idle fairly well.  The secret to getting efi to really
control A/F under these circumstances would be to at least get the engine to
stumble and blow raw fuel into the exhaust fairly consistently.  If the
anomalies approaches any type of periodicity, then you can predict the next
event with a definable level of certainty (and write code to correct for
it).  

A computer with enough overhead to measure engine speed (and therefore
detect surges and power drop offs) every 5-6 degrees like the EFI332 project
does would be necessary.  But it would also have to look at O2, EGT and MAP
or MAF (to detect regurge backing up in the intake) and the system would
have to have a separate algorithm to handle this (out of map) situation.
Even at that, to get any kind of consistency would probably require multiple
O2 sensors (EGT isn't going to be very useful as most of the fuel isn't
getting burned in this situation!) and an averaging algorithm to come up
with an "average" A/F and compare this to A/F at specific points in the
exhaust header (to detect rich slugs in the exhaust).  This information
could then be used to measure the amount of correction necessary in the next
event and when the correction needed to be made prior to the next event.  

Rick
 



> -----Original Message-----
> From:	EFISYSTEMS at aol.com [SMTP:EFISYSTEMS at aol.com]
> Sent:	Tuesday, December 01, 1998 3:11 AM
> To:	diy_efi at efi332.eng.ohio-state.edu
> Subject:	Re: ox sensor on sequential efi,high overlap cam....
> 
> In a message dated 11/25/98 12:16:04 AM Pacific Standard Time,
> mwichstr at online.no writes:
> 
> << From:	mwichstr at online.no (Espen Hilde)
>  Sender:	owner-diy_efi at efi332.eng.ohio-state.edu
>  Reply-to:	diy_efi at efi332.eng.ohio-state.edu
>  To:	diy_efi at efi332.eng.ohio-state.edu
>  
>  I have a question that I have been thinking about lately.
>  In a engine with high overlap cam and sequential efi,how to measure air
>  fuel ratio?
>  At certain points in the rpm scale the engine is scavenging air right
>  trough the engine.(I presume)
>  At overlap.The sequential efi will not inject fuel to this amount of
>  air.(not supposed to....)
>  The result as I see it,is that air is pulled trough to the exhaust
>  system.The ox sensor (if it sensors 02)
>  will say this is a lean condition.
>  Am I worthy of a coned shaped hat?
>  Espen Hilde 
>  
>  Hi Espen
>      In my expereince,  I have noticed Oxygen will transport to the
> exhaust
> during a missfire or through heavy overlap cycles.............but with a
> wide
> range O2 sensor which is supposed to concentrate on HC, it does not always
> translate,,,at this point it is good to monitor EGT as well as long as it
> is
> close enough so that you can get a reasonable transport delay
> reaction.....hth's
> -Carl Summers