Flywheel/Encoder patterns

[Roy]

kleenair at ix.netcom.com wrote:
> 
> A few days ago I mentioned that maybe by looking at the ionization
> current in a coil per plug system we can determine whether a spark
> occured on top of the compression stroke or on top of the exhaust stroke.
>  Monitoring the ionization current can be complex, but how about
> monitoring spark duration?
> 
> I read an SAE paper (#960329) about a spark controller that feeds back
> the duration of spark.  This is accomplished by measuring the flyback
> voltage on the primary side of the coil.  The purpose of the paper is to
> use this info to optimize dwell (as opposed to using a fixed high value
> all the time).
> 
> My question is:  Is there a relationship between spark DURATION and
> combustion chamber pressure?  If so, any guesses as to what the
> relationship is?
> 
> Happy Holidays,
> 
> Mazda


Reply from Spectric at Globalnet.co.uk

If you examine the secondary waveform of an ignition system you will see
that the duration of the spark is constant under a certain situation for
all cylinders, even when you have no presure on one of them.  The
voltage on this cylinder will also be much less because of no cylinder
pressure.  All modern ignition systems control the dwell period
electronically, maintaining maximum coil saturation at all engine
speeds.  This is often done using low impedance coils and constant
current drivers.