Knock sensors

[Todd Knighton]

Robert J. Harris wrote:
> 
> Dumb Idea forming - maybe.  By knock sensor, I assume we mean
> the knock caused by the fuel air mixture igniting prior to the timed
> spark - generally at medium load and rpm.  Since this occurs before
> the timed spark, nothing you can do to the timed spark directly
> affects the knock.  Retarding the spark lowers power thereby
> lowering the temp/pressure part of the equation - eliminates
> knock.

Nope, we were talking about knock caused by ignition timing being set
too early, not Pre-ignition caused by hot spots, carbon buildup, or
improper heat range of spark plugs.
> 
> Why not use the sensor to directly change a parameter that
> controls knock - temperature?    Instead of retarding timing and
> losing power - why not richen mixture?  More fuel - more  evaporative
> cooling - lower temp - rat noww
> 
> Richening mixture small amount has no negative effect on power.
> Early turbos (pre EFI and intercoolers) often ran as high as 40% rich
> to cool the charge to keep from detonating.
> 
> Simple algorithm -  already have feedback loop for O2 sensor.  Step
> bang the correction a fixed ammout richer.  O2 sensor corrects back
> over time.  No more knock, no power loss, far less critical to tune,
> no need to f with ignition timing and if it false alarms - worst effect is
> lowered fuel mileage.
> 
> Just a thought for what its worth


this all might work for pre-ignition, but not the knock sensing we're
talking about.
Though, richening the mixture does tend to slow the burn rate of the
mixture, thus even if the timing is set too early, it typically won't
knock.  Talk to Autothority about this, they're the kings of too much
advance and too much fuel.  Maybe that's how they get those magical 25%
increases over stock!  ;)

Todd Knighton
Protomotive Engineering