Knock sensor

Pete Paraska paraska at
Thu Jul 21 14:51:10 GMT 1994

Dave Williams wrote:
> SAAB's Trionic engine management system drops voltage after the initial
>spark, then looks at the resistance of the plug gap.  SAAB claims they
>can tell if the cylinder is running into detonation by looking at this

Just interested in other's ideas how this might actually work.  How could 
plug gap resistance after the spark tell you anything about detonation?  Can 
the plug gap "taste" the residue of preignition as being different from the 
"taste" (er..resistance) of a slowly propagting flame front that results 
from correct ignition?  

It's an interesting concept, though, using plug gap resistance to measure 
detonation.  If it was repeatable and reliable, it would seem to be better 
than trying to guess what that accelerometer (knock sensor) was REALLY 
telling you.
It seems that all this filtering, amplifying, etc. and making assumptions 
about what frequency is actually indicative of detonation involves several 
leaps of faith.

 ~~~~~~~~ Pete (paraska at          IZCC#15 ~~~~~~~~~

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