Flywheel/Encoder patterns

[kleenair at ix.netcom.com]

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